Operating System and Installation

The haplo.stats package has been uploaded to the Comprehensive R Archive Network (CRAN), and is made available on various operating systems through CRAN. Package installation within R is made simple from within R using install.packages(‘haplo.stats’), but other procedures for installing R packages can be found at the R project website.

The routines are computationally intensive and return lots of information in the returned object. Therefore, we assign classes to the returned objects and provide various methods (e.g., print, summary, plot) for each of them.

Data Setup

We first show some typical steps when you first load a package and look for details on a function of interest. In the sample code below, we load the package, check which functions are available in the package, view a help file, and run the example that is within the help file.

# load the library, load and preview at demo dataset
library(haplo.stats)
ls(name = "package:haplo.stats")
help(haplo.em)
example(haplo.em)

options(width = 100)
rm(list = ls())
require(haplo.stats)

Loading required package: haplo.stats

Loading required package: arsenal

Example Data

The package package contains three example data sets. The primary data set used in this manual is named hla.demo, which contains 11 loci from the HLA region on chromosome 6, with covariates, qualitative, and quantitative responses. Since the data is provided in the package, we load the data in R using data() and view the names of the columns. Then to make the columns of hla.demo accessible without typing it each time, we attach it to the current session.

# load and preview demo dataset stored in ~/haplo.stats/data/hla.demo.tab
data(hla.demo)
names(hla.demo)

 [1] "resp"     "resp.cat" "male"     "age"      "DPB.a1"   "DPB.a2"   "DPA.a1"   "DPA.a2"  
 [9] "DMA.a1"   "DMA.a2"   "DMB.a1"   "DMB.a2"   "TAP1.a1"  "TAP1.a2"  "TAP2.a1"  "TAP2.a2" 
[17] "DQB.a1"   "DQB.a2"   "DQA.a1"   "DQA.a2"   "DRB.a1"   "DRB.a2"   "B.a1"     "B.a2"    
[25] "A.a1"     "A.a2"    

# attach hla.demo to make columns available in the session attach(hla.demo)

The column names of _hla.demo are shown above. They are defined as follows:

• resp: quantitative antibody response to measles vaccination
• resp.cat: a factor with levels “low”, “normal”, “high”, for categorical antibody response
• male: gender code with 1=“male”, 0=“female”
• age: age (in months) at immunization

The remaining columns are genotypes for 11 HLA loci, with a prefix name (e.g., “DQB”) and a suffix for each of two alleles (“.a1” and “.a2”).

Creating a Genotype Matrix

Many of the functions require a matrix of genotypes, denoted below as geno. This matrix is arranged such that each locus has a pair of adjacent columns of alleles, and the order of columns corresponds to the order of loci on a chromosome. If there are K loci, then the number of columns of * geno* is \(2K\). Rows represent the alleles for each subject. For example, if there are three loci, in the order A-B-C, then the 6 columns of * geno* would be arranged as A.a1, A.a2, B.a1, B.a2, C.a1, C.a2. For illustration, three of the loci in * hla.demo* will be used to demonstrate some of the functions. Create a separate data frame for 3 of the loci, and call this * geno*. Then create a vector of labels for the loci.

geno <- hla.demo[, c(17, 18, 21:24)]
genolabel <- c("DQB", "DRB", "B")

The * hla.demo* data already had alleles in two columns for each locus. For many SNP datasets, the data is in a one column format, giving the count of the minor allele. To assist in converting this format to two columns, a function named * geno1to2* has been added to the package. See its help file for more details.

Preview Missing Data: summaryGeno

Before performing a haplotype analysis, the user will want to assess missing genotype data to determine the completeness of the data. If many genotypes are missing, the functions may take a long time to compute results, or even run out of memory. For these reasons, the user may want to remove some of the subjects with a lot of missing data. This step can be guided by using the summaryGeno function, which checks for missing allele information and counts the number of potential haplotype pairs that are consistent with the observed data (see the Appendix for a description of this counting scheme).

The codes for missing alleles are defined by the parameter miss.val, a vector to define all possible missing value codes. Below, the result is saved in geno.desc, which is a data frame, so individual rows may be printed. Here we show the results for subjects 1-10, 80-85, and 135-140, some of which have missing alleles.

geno.desc <- summaryGeno(geno, miss.val = c(0, NA))
print(geno.desc[c(1:10, 80:85, 135:140), ])

    missing0 missing1 missing2 N.enum.rows
1          3        0        0           4
2          3        0        0           4
3          3        0        0           4
4          3        0        0           2
5          3        0        0           4
6          3        0        0           2
7          3        0        0           4
8          3        0        0           2
9          3        0        0           2
10         3        0        0           1
80         3        0        0           4
81         2        0        1        1800
82         3        0        0           2
83         3        0        0           1
84         3        0        0           2
85         3        0        0           4
135        3        0        0           4
136        3        0        0           2
137        1        0        2      129600
138        3        0        0           4
139        3        0        0           4
140        3        0        0           4

The columns with ‘loc miss-’ illustrate the number of loci missing either 0, 1, or 2 alleles, and the last column, num_enum_rows, illustrates the number of haplotype pairs that are consistent with the observed data. In the example above, subjects indexed by rows 81 and 137 have missing alleles. Subject #81 has one locus missing two alleles, while subject #137 has two loci missing two alleles. As indicated by num_enum_rows, subject #81 has 1,800 potential haplotype pairs, while subject #137 has nearly 130,000.

The 130,000 haplotype pairs is considered a large number, but haplo.em, haplo.score, and haplo.glm complete in roughly 3-6 minutes (depending on system limits or control parameter settings). If person #137 were removed, the methods would take less than half that time. It is preferred to keep people if they provide information to the analysis, given that run time and memory usage are not too much of a burden.

When a person has no genotype information, they do not provide information to any of the methods in . Furthermore, they cause a much longer run time. Below, using the table function on the third column of geno.desc, we can tabulate how many people are missing two alleles at any at of the three loci. If there were people missing two alleles at all three loci, they should be removed. The second command below shows how to make an index of which people to remove from hla.demo because they are missing all their alleles.

# how many samples missing 2 alleles at the 3 markers
table(geno.desc[, 3])

  0   1   2 
218   1   1 

## create an index of people missing all alleles
miss.all <- which(geno.desc[, 3] == 3)

# use index to subset hla.demo
hla.demo.updated <- hla.demo[-miss.all, ]

Random Numbers and Setting Seed

Random numbers are used in several of the functions (e.g., to determine random starting frequencies within haplo.em, and to compute permutation p-values in haplo.score). To reproduce calculations involving random numbers, we use set.seed() before any function that uses random numbers. We illustrate setting the seed below.

# this is how to set the seed for reproducing results where haplo.em is involved, and also if
# simulations are run. In practice, don't reset seed.
seed <- c(17, 53, 1, 40, 37, 0, 62, 56, 5, 52, 12, 1)
set.seed(seed)

Algorithm

For genetic markers measured on unrelated subjects, with linkage phase unknown, haplo.em computes maximum likelihood estimates of haplotype probabilities. Because there may be more than one pair of haplotypes that are consistent with the observed marker phenotypes, posterior probabilities of haplotype pairs for each subject are also computed. Unlike the usual EM which attempts to enumerate all possible haplotype pairs before iterating over the EM steps, our “progressive insertion” algorithm progressively inserts batches of loci into haplotypes of growing lengths, runs the EM steps, trims off pairs of haplotypes per subject when the posterior probability of the pair is below a specified threshold, and then continues these insertion, EM, and trimming steps until all loci are inserted into the haplotype. The user can choose the batch size. If the batch size is chosen to be all loci, and the threshold for trimming is set to 0, then this reduces to the usual EM algorithm. The basis of this progressive insertion algorithm is from the “snphap” software by David Clayton. Although some of the features and control parameters of haplo.em are modeled after snphap, there are substantial differences, such as extension to allow for more than two alleles per locus, and some other nuances on how the algorithm is implemented.

Example Usage haplo.em()

We use haplo.em on geno for the 3 loci defined above and save the result in an object named save.em, which has the haplo.em class. The print method would normally print all 178 haplotypes from save.em, but to keep the results short for this manual, we give a quick glance of the output by using the option nlines=10, which prints only the first 10 haplotypes of the full results. The nlines parameter has been employed in some of Haplo Stats’ print methods for when there are many haplotypes. In practice, it is best to exclude this parameter so that the default will print all results.

save.em <- haplo.em(geno = geno, locus.label = genolabel, miss.val = c(0, NA))
names(save.em)

 [1] "lnlike"        "lnlike.noLD"   "lr"            "df.lr"         "hap.prob"      "hap.prob.noLD"
 [7] "converge"      "locus.label"   "indx.subj"     "subj.id"       "post"          "hap1code"     
[13] "hap2code"      "haplotype"     "nreps"         "rows.rem"      "max.pairs"     "control"      

print(save.em, nlines = 10)

==================================================================================================== 
                                             Haplotypes                                              
==================================================================================================== 
   DQB DRB  B hap.freq
1   21   1  8  0.00232
2   21   2  7  0.00227
3   21   2 18  0.00227
4   21   3  8  0.10408
5   21   3 18  0.00229
6   21   3 35  0.00570
7   21   3 44  0.00378
8   21   3 45  0.00227
9   21   3 49  0.00227
10  21   3 57  0.00227
==================================================================================================== 
                                              Details                                                
==================================================================================================== 
lnlike =  -1847.675 
lr stat for no LD =  632.5085 , df =  125 , p-val =  0 

The print methods shows the haplotypes and their estimated frequencies, followed by the final log-likelihood statistic and the lr stat for no LD, which is the likelihood ratio test statistic contrasting the lnlike for the estimated haplotype frequencies versus the lnlike under the null assuming that alleles from all loci are in linkage equilibrium. We note that the trimming by the progressive insertion algorithm can invalidate the lr stat and the degrees of freedom (df).\

Summary Method

The summary method for a haplo.em object on save.em shows the list of haplotypes per subject, and their posterior probabilities:

summary(save.em, nlines = 7)

==================================================================================================== 
                       Subjects: Haplotype Codes and Posterior Probabilities                         
==================================================================================================== 
  subj.id hap1 hap2 posterior
1       1   58   78   1.00000
2       2   17  138   0.87468
3       2   13  143   0.12532
4       3   25  168   1.00000
5       4   17   38   0.71379
6       4   13   39   0.28621
7       5   55   94   1.00000
==================================================================================================== 
                               Number of haplotype pairs: max vs used                                
==================================================================================================== 
        
x          1   2   3  84 135
  1       18   0   0   0   0
  2       50   4   0   0   0
  4      116  29   1   0   0
  1800     0   0   0   1   0
  129600   0   0   0   0   1

The first part of the summary output lists the subject id (row number of input geno matrix), the codes for the haplotypes of each pair, and the posterior probabilities of the haplotype pairs. The second part gives a table of the maximum number of pairs of haplotypes per subject, versus the number of pairs used in the final posterior probabilities. The haplotype codes remove the clutter of illustrating all the alleles of the haplotypes, but may not be as informative as the actual haplotypes themselves. To see the actual haplotypes, use the show.haplo=TRUE option, as in the following example.

# show full haplotypes, instead of codes
summary(save.em, show.haplo = TRUE, nlines = 7)

==================================================================================================== 
                       Subjects: Haplotype Codes and Posterior Probabilities                         
==================================================================================================== 
  subj.id hap1.DQB hap1.DRB hap1.B hap2.DQB hap2.DRB hap2.B posterior
1       1       31       11     61       32        4     62   1.00000
2       2       21        7     44       62        2      7   0.87468
3       2       21        7      7       62        2     44   0.12532
4       3       31        1     27       63       13     62   1.00000
5       4       21        7     44       31        7      7   0.71379
6       4       21        7      7       31        7     44   0.28621
7       5       31       11     51       42        8     55   1.00000
==================================================================================================== 
                               Number of haplotype pairs: max vs used                                
==================================================================================================== 
        
x          1   2   3  84 135
  1       18   0   0   0   0
  2       50   4   0   0   0
  4      116  29   1   0   0
  1800     0   0   0   1   0
  129600   0   0   0   0   1

# demonstrate only the syntax of control parameters
save.em.try20 <- haplo.em(geno = geno, locus.label = genolabel, miss.val = c(0, NA), control = haplo.em.control(n.try = 20,
    insert.batch.size = 2))

Haplotype Frequencies by Group Subsets

To compute the haplotype frequencies for each level of a grouping variable, use the function haplo.group. The following example illustrates the use of a binomial response based on resp.cat, y.bin, that splits the subjects into two groups.

## run haplo.em on sub-groups create ordinal and binary variables
y.bin <- 1 * (hla.demo$resp.cat == "low")
group.bin <- haplo.group(y.bin, geno, locus.label = genolabel, miss.val = 0)
print(group.bin, nlines = 15)

---------------------------------------------------------------------------------------------------- 
                                 Counts per Grouping Variable Value                                  
---------------------------------------------------------------------------------------------------- 
group
  0   1 
157  63 


---------------------------------------------------------------------------------------------------- 
                                  Haplotype Frequencies By Group                                     
---------------------------------------------------------------------------------------------------- 
   DQB DRB  B   Total y.bin.0 y.bin.1
1   21   1 62      NA      NA 0.00794
2   21   1  8 0.00232 0.00335      NA
3   21  10  8 0.00181 0.00318      NA
4   21  13  8 0.00274      NA      NA
5   21   2 18 0.00227 0.00318      NA
6   21   2  7 0.00227 0.00318      NA
7   21   3 18 0.00229 0.00637      NA
8   21   3 35 0.00570 0.00639      NA
9   21   3 44 0.00378 0.00333 0.01587
10  21   3 45 0.00227      NA      NA
11  21   3 49 0.00227      NA      NA
12  21   3 57 0.00227      NA      NA
13  21   3 70 0.00227      NA 0.00000
14  21   3  8 0.10408 0.06974 0.19048
15  21   4 14      NA 0.00637      NA

The group.bin object can be very large, depending on the number of possible haplotypes, so only a portion of the output is illustrated above (limited again by nlines). The first section gives a short summary of how many subjects appear in each of the groups. The second section is a table with the following columns: row numbers, the alleles of the haplotypes, then Total is the estimated haplotype frequencies for the entire data set. The last columns are the estimated haplotype frequencies for the subjects in the levels of the group variable (y.bin=0 and y.bin=1 in this example). Note that some haplotype frequencies have an NA, which appears when the haplotypes do not occur in the subgroups.

Quantitative Traits: haplo.power.qt

We assume that quantitative traits will be modeled by a linear regression. Some well-known tests for association between haplotypes and the trait include score statistics and an F-test by Zaykin. For both types of tests, power depends on the amount of variance in the trait that is explained by haplotypes, or a multiple correlation coefficient, \(R^{2}\). Rather than specifying the haplotype coefficients directly, we calculate the vector of coefficients based on an \(R^{2}\) value.

In the example below, we load an example set of haplotypes that contain 5 markers, and specify the indices of the at-risk haplotypes; in this case, whichever haplotype has allele \(1\) at the 2nd and 3rd markers.
We set the first haplotype (most common) as the baseline. With these values we calculate the vector of coefficients for haplotype effects from find.haplo.beta.qt using an \(R^{2}=0.01\).
Next, we use haplo.power.qt to calculate the sample size for the set of haplotypes and their coefficients, type-I error (alpha) set to \(0.05\), power at 80%, and the same mean and variance used to get haplotype coefficients.
Then we use the sample size needed for 80% power for un-phased haplotypes (\(2,826\)) to get the power for both phased and un-phased haplotypes.

# load a set of haplotypes

data(hapPower.demo)

#### an example using save.em hla markers may go like this.  keep <- which(save.em$hap.prob > .004)
#### # get an index of non-rare haps hfreq <- save.em$hap.prob[keep] hmat <-
#### save.em$haplotype[keep,] hrisk <- which(hmat[,1]==31 & hmat[,2]==11) # contains 3 haps with
#### freq=.01 hbase <- 4 # 4th hap has mas freq of .103

## separate the haplotype matrix and the frequencies
hmat <- hapPower.demo[, -6]
hfreq <- hapPower.demo[, 6]

## Define risk haplotypes as those with '1' allele at loc2 and loc3
hrisk <- which(hmat$loc.2 == 1 & hmat$loc.3 == 1)

# define index for baseline haplotype
hbase <- 1

hbeta.list <- find.haplo.beta.qt(haplo = hmat, haplo.freq = hfreq, base.index = hbase, haplo.risk = hrisk,
    r2 = 0.01, y.mu = 0, y.var = 1)
hbeta.list

$r2
[1] 0.01

$beta
 [1] -0.03892497  0.00000000  0.00000000  0.00000000  0.00000000  0.00000000  0.00000000  0.27636731
 [9]  0.00000000  0.27636731  0.00000000  0.00000000  0.00000000  0.00000000  0.00000000  0.27636731
[17]  0.27636731  0.00000000  0.00000000  0.00000000  0.00000000

$base.index
[1] 1

$haplo.risk
[1]  8 10 16 17

ss.qt <- haplo.power.qt(hmat, hfreq, hbase, hbeta.list$beta, y.mu = 0, y.var = 1, alpha = 0.05, power = 0.8)
ss.qt

$ss.phased.haplo
[1] 2091

$ss.unphased.haplo
[1] 2826

$power.phased.haplo
[1] 0.8

$power.unphased.haplo
[1] 0.8

power.qt <- haplo.power.qt(hmat, hfreq, hbase, hbeta.list$beta, y.mu = 0, y.var = 1, alpha = 0.05, sample.size = 2826)
power.qt

$ss.phased.haplo
[1] 2826

$ss.unphased.haplo
[1] 2826

$power.phased.haplo
[1] 0.9282451

$power.unphased.haplo
[1] 0.8000592

Case-Control Studies: haplo.power.cc

The steps to compute sample size and power for case-control studies is similar to the steps for quantitative traits. If we assume a log-additive model for haplotype effects, the haplotype coefficients can be specified first as odds ratios (OR), and then converted to logistic regression coefficients according to \(log(OR)\).

In the example below, we assume the same baseline and risk haplotypes defined above, give the risk haplotypes an odds ratio of 1.50, and specify a population disease prevalance of 10%. We also assume cases make up 50% (case.frac) of the study subjects. We first compute the sample size for this scenario for Type-I error (alpha) at \(0.05\) and 80% power, and then compute power for the sample size required for un-phased haplotypes (\(4,566\)).

## get power and sample size for quantitative response get beta vector based on odds ratios

cc.OR <- 1.5

# determine beta regression coefficients for risk haplotypes

hbeta.cc <- numeric(length(hfreq))
hbeta.cc[hrisk] <- log(cc.OR)

# Compute sample size for stated power

ss.cc <- haplo.power.cc(hmat, hfreq, hbase, hbeta.cc, case.frac = 0.5, prevalence = 0.1, alpha = 0.05,
    power = 0.8)
ss.cc

$ss.phased.haplo
[1] 3454

$ss.unphased.haplo
[1] 4566

$power.phased.haplo
[1] 0.8

$power.unphased.haplo
[1] 0.8

# Compute power for given sample size

power.cc <- haplo.power.cc(hmat, hfreq, hbase, hbeta.cc, case.frac = 0.5, prevalence = 0.1, alpha = 0.05,
    sample.size = 4566)
power.cc

$ss.phased.haplo
[1] 4566

$ss.unphased.haplo
[1] 4566

$power.phased.haplo
[1] 0.9206568

$power.unphased.haplo
[1] 0.8000695

Quantitative Trait Analysis

First, we assess a haplotype association with a quantitative trait in hla.demo called resp. To tell haplo.score the trait is quantitative, specify the parameter trait.type=“gaussian” (a reminder that a gaussian distribution is assumed for the error terms). The other arguments, all set to default values, are explained in the help file. Note that rare haplotypes can result in unstable variance estimates, and hence unreliable test statistics for rare haplotypes. We restrict the analysis to get scores for haplotypes with a minimum sample count using min.count=5. Below is an example of running haplo.score with a quantitative trait, then viewing the results using the print method for the haplo.score class. (again, output shortened by nlines).

# score statistics w/ Gaussian trait
score.gaus.add <- haplo.score(hla.demo$resp, geno, trait.type = "gaussian", min.count = 5, locus.label = genolabel,
    simulate = FALSE)
print(score.gaus.add, nlines = 10)

---------------------------------------------------------------------------------------------------- 
                                  Haplotype Effect Model: additive                                   
---------------------------------------------------------------------------------------------------- 
---------------------------------------------------------------------------------------------------- 
                                      Global Score Statistics                                        
---------------------------------------------------------------------------------------------------- 

global-stat = 30.6353, df = 18, p-val = 0.03171

---------------------------------------------------------------------------------------------------- 
                                     Haplotype-specific Scores                                       
---------------------------------------------------------------------------------------------------- 

      DQB DRB B  Hap-Freq Hap-Score p-val  
 [1,] 21  3   8  0.10408  -2.39631  0.01656
 [2,] 31  4   44 0.02849  -2.24273  0.02491
 [3,] 51  1   44 0.01731  -0.99357  0.32043
 [4,] 63  13  44 0.01606  -0.84453  0.39837
 [5,] 63  2   7  0.01333  -0.50736  0.6119 
 [6,] 32  4   60 0.0306   -0.46606  0.64118
 [7,] 21  7   44 0.02332  -0.41942  0.67491
 [8,] 62  2   44 0.01367  -0.26221  0.79316
 [9,] 62  2   18 0.01545  -0.21493  0.82982
[10,] 51  1   27 0.01505  0.01539   0.98772

Binary Trait Analysis

Let us assume that “low” responders are of primary interest, so we create a binary trait that has values of 1 when resp.cat is “low”, and 0 otherwise. Then in haplo.score specify the parameter trait.type=“binomial”.

# scores, binary trait
y.bin <- 1 * (hla.demo$resp.cat == "low")
score.bin <- haplo.score(y.bin, geno, trait.type = "binomial", x.adj = NA, min.count = 5, haplo.effect = "additive",
    locus.label = genolabel, miss.val = 0, simulate = FALSE)
print(score.bin, nlines = 10)

---------------------------------------------------------------------------------------------------- 
                                  Haplotype Effect Model: additive                                   
---------------------------------------------------------------------------------------------------- 
---------------------------------------------------------------------------------------------------- 
                                      Global Score Statistics                                        
---------------------------------------------------------------------------------------------------- 

global-stat = 33.70125, df = 18, p-val = 0.01371

---------------------------------------------------------------------------------------------------- 
                                     Haplotype-specific Scores                                       
---------------------------------------------------------------------------------------------------- 

      DQB DRB B  Hap-Freq Hap-Score p-val  
 [1,] 62  2   7  0.05098  -2.19387  0.02824
 [2,] 51  1   35 0.03018  -1.58421  0.11315
 [3,] 63  13  7  0.01655  -1.56008  0.11874
 [4,] 21  7   7  0.01246  -1.47495  0.14023
 [5,] 32  4   7  0.01678  -1.00091  0.31687
 [6,] 32  4   62 0.02349  -0.6799   0.49657
 [7,] 51  1   27 0.01505  -0.66509  0.50599
 [8,] 31  11  35 0.01754  -0.5838   0.55936
 [9,] 31  11  51 0.01137  -0.43721  0.66196
[10,] 51  1   44 0.01731  0.00826   0.99341

Ordinal Trait Analysis

To create an ordinal trait, here we convert resp.cat (described above) to numeric values, y.ord (with levels 1, 2, 3). For haplo.score, use y.ord as the response variable, and set the parameter trait.type = “ordinal”.

# scores w/ ordinal trait
y.ord <- as.numeric(hla.demo$resp.cat)
score.ord <- haplo.score(y.ord, geno, trait.type = "ordinal", x.adj = NA, min.count = 5, locus.label = genolabel,
    miss.val = 0, simulate = FALSE)
print(score.ord, nlines = 7)

---------------------------------------------------------------------------------------------------- 
                                  Haplotype Effect Model: additive                                   
---------------------------------------------------------------------------------------------------- 
---------------------------------------------------------------------------------------------------- 
                                      Global Score Statistics                                        
---------------------------------------------------------------------------------------------------- 

global-stat = 15.23209, df = 18, p-val = 0.64597

---------------------------------------------------------------------------------------------------- 
                                     Haplotype-specific Scores                                       
---------------------------------------------------------------------------------------------------- 

     DQB DRB B  Hap-Freq Hap-Score p-val  
[1,] 32  4   62 0.02349  -2.17133  0.02991
[2,] 21  3   8  0.10408  -1.34661  0.17811
[3,] 32  4   7  0.01678  -1.09487  0.27357
[4,] 62  2   7  0.05098  -0.96874  0.33268
[5,] 21  7   44 0.02332  -0.83747  0.40233
[6,] 63  13  7  0.01655  -0.80787  0.41917
[7,] 21  7   7  0.01246  -0.63316  0.52663

Haplotype Scores, Adjusted for Covariates

To adjust for covariates in haplo.score, first set up a matrix of covariates from the example data. For example, use a column for male (1 if male; 0 if female), and a second column for age. Then pass the matrix to haplo.score using parameter x.adj. The results change slightly in this example.

# score w/gaussian, adjusted by covariates
x.ma <- with(hla.demo, cbind(male, age))
score.gaus.adj <- haplo.score(hla.demo$resp, geno, trait.type = "gaussian", x.adj = x.ma, min.count = 5,
    locus.label = genolabel, simulate = FALSE)
print(score.gaus.adj, nlines = 10)

---------------------------------------------------------------------------------------------------- 
                                  Haplotype Effect Model: additive                                   
---------------------------------------------------------------------------------------------------- 
---------------------------------------------------------------------------------------------------- 
                                      Global Score Statistics                                        
---------------------------------------------------------------------------------------------------- 

global-stat = 31.02908, df = 18, p-val = 0.02857

---------------------------------------------------------------------------------------------------- 
                                     Haplotype-specific Scores                                       
---------------------------------------------------------------------------------------------------- 

      DQB DRB B  Hap-Freq Hap-Score p-val  
 [1,] 21  3   8  0.10408  -2.4097   0.01597
 [2,] 31  4   44 0.02849  -2.25293  0.02426
 [3,] 51  1   44 0.01731  -0.98763  0.32333
 [4,] 63  13  44 0.01606  -0.83952  0.40118
 [5,] 63  2   7  0.01333  -0.48483  0.6278 
 [6,] 32  4   60 0.0306   -0.46476  0.64211
 [7,] 21  7   44 0.02332  -0.41249  0.67998
 [8,] 62  2   44 0.01367  -0.26443  0.79145
 [9,] 62  2   18 0.01545  -0.20425  0.83816
[10,] 51  1   27 0.01505  0.02243   0.9821 

Plots and Haplotype Labels

A convenient way to view results from haplo.score is a plot of the haplotype frequencies (Hap-Freq) versus the haplotype score statistics (Hap-Score). This plot, and the syntax for creating it, are shown in the figure below.

Some points on the plot may be of interest. To identify individual points on the plot, use locator.haplo(score.gaus), which is similar to locator(). Use the mouse to select points on the plot. After points are chosen, click on the middle mouse button, and the points are labeled with their haplotype labels. Note, in constructing the figure, we had to define which points to label, and then assign labels in the same way as done within the locator.haplo()* function.

## plot score vs. frequency, gaussian response
plot(score.gaus.add, pch = "o")

## locate and label pts with their haplotypes works similar to locator() function > pts.haplo <-
## locator.haplo(score.gaus)

pts.haplo <- list(x.coord = c(0.05098, 0.03018, 0.1), y.coord = c(2.1582, 0.45725, -2.1566), hap.txt = c("62:2:7",
    "51:1:35", "21:3:8"))

text(x = pts.haplo$x.coord, y = pts.haplo$y.coord, labels = pts.haplo$hap.txt)

Skipping Rare Haplotypes

For the haplo.score, the skip.haplo and min.count parameters control which rare haplotypes are pooled into a common group. The min.count parameter is a recent addition to haplo.score, yet it does the same task as skip.haplo and is the same idea as haplo.min.count used in haplo.glm.control for haplo.glm. As a guideline, you may wish to set min.count to calculate scores for haplotypes with expected haplotype counts of \(5\) or greater in the sample. We concentrate on this expected count because it adjusts to the size of the input data. If \(N\) is the number of subjects and \(f\) the haplotype frequency, then the expected haplotype count is . Alternatively, you can choose .

In the following example we try a different cut-off than before, min.count=10, which corresponds to skip.haplo of \(10 \div (2 \times 220) = .045\). In the output, see that the global statistic, degrees of freedom, and p-value change because of the fewer haplotypes, while the haplotype-specific scores do not change.

# increase skip.haplo, expected hap counts = 10
score.gaus.min10 <- haplo.score(hla.demo$resp, geno, trait.type = "gaussian", x.adj = NA, min.count = 10,
    locus.label = genolabel, simulate = FALSE)
print(score.gaus.min10)

---------------------------------------------------------------------------------------------------- 
                                  Haplotype Effect Model: additive                                   
---------------------------------------------------------------------------------------------------- 
---------------------------------------------------------------------------------------------------- 
                                      Global Score Statistics                                        
---------------------------------------------------------------------------------------------------- 

global-stat = 20.66451, df = 7, p-val = 0.0043

---------------------------------------------------------------------------------------------------- 
                                     Haplotype-specific Scores                                       
---------------------------------------------------------------------------------------------------- 

     DQB DRB B  Hap-Freq Hap-Score p-val  
[1,] 21  3   8  0.10408  -2.39631  0.01656
[2,] 31  4   44 0.02849  -2.24273  0.02491
[3,] 32  4   60 0.0306   -0.46606  0.64118
[4,] 21  7   44 0.02332  -0.41942  0.67491
[5,] 51  1   35 0.03018  0.69696   0.48583
[6,] 32  4   62 0.02349  2.37619   0.01749
[7,] 62  2   7  0.05098  2.39795   0.01649

Haplotype Model Effect

The haplo.score() function allows non-additive effects for scoring haplotypes. The possible effects for haplotypes are additive, dominant, and recessive. Under recessive effects, fewer haplotypes may be scored, because subjects are required to be homozygous for haplotypes. Furthermore, there would have to be min.count such persons in the sample to have the recessive effect scored. Therefore, a recessive model should only be used on samples with common haplotypes. In the example below with the gaussian response, set the haplotype effect to dominant using parameter haplo.effect = ‘’dominant’’. Notice the results change slightly compared to the score.gaus.add results above.

# score w/gaussian, dominant effect

score.gaus.dom <- haplo.score(hla.demo$resp, geno, trait.type = "gaussian", x.adj = NA, min.count = 5,
    haplo.effect = "dominant", locus.label = genolabel, simulate = FALSE)
print(score.gaus.dom, nlines = 10)

---------------------------------------------------------------------------------------------------- 
                                  Haplotype Effect Model: dominant                                   
---------------------------------------------------------------------------------------------------- 
---------------------------------------------------------------------------------------------------- 
                                      Global Score Statistics                                        
---------------------------------------------------------------------------------------------------- 

global-stat = 29.56133, df = 18, p-val = 0.04194

---------------------------------------------------------------------------------------------------- 
                                     Haplotype-specific Scores                                       
---------------------------------------------------------------------------------------------------- 

      DQB DRB B  Hap-Freq Hap-Score p-val  
 [1,] 21  3   8  0.10408  -2.23872  0.02517
 [2,] 31  4   44 0.02849  -2.13233  0.03298
 [3,] 51  1   44 0.01731  -0.99357  0.32043
 [4,] 63  13  44 0.01606  -0.84453  0.39837
 [5,] 63  2   7  0.01333  -0.50736  0.6119 
 [6,] 32  4   60 0.0306   -0.46606  0.64118
 [7,] 21  7   44 0.02332  -0.41942  0.67491
 [8,] 62  2   44 0.01367  -0.26221  0.79316
 [9,] 62  2   18 0.01545  -0.21493  0.82982
[10,] 51  1   27 0.01505  0.01539   0.98772

Simulation p-values

When simulate=TRUE, haplo.score gives simulated p-values.
Simulated haplotype score statistics are the re-calculated score statistics from a permuted re-ordering of the trait and covariates and the original ordering of the genotype matrix. The simulated p-value for the global score statistic (Global sim. p-val) is the number of times the simulated global score statistic exceeds the observed, divided by the total number of simulations. Likewise, simulated p-value for the maximum score statistic (Max-stat sim. p-val*) is the number of times the simulated maximum haplotype score statistic exceeds the observed maximum score statistic, divided by the total number of simulations. The maximum score statistic is the maximum of the square of the haplotype-specific score statistics, which has an unknown distribution, so its significance can only be given by the simulated p-value.
Intuitively, if only one or two haplotypes are associated with the trait, the maximum score statistic should have greater power to detect association than the global statistic.

The score.sim.control function manages control parameters for simulations. The haplo.score function employs the simulation p-value precision criteria of Besag and Clifford.
These criteria ensure that the simulated p-values for both the global and the maximum score statistics are precise for small p-values.
The algorithm performs a user-defined minimum number of permutations (min.sim) to guarantee sufficient precision for the simulated p-values for score statistics of individual haplotypes. Permutations beyond this minimum are then conducted until the sample standard errors for simulated p-values for both the global-stat and {} provides a two-sided 95% confidence interval for the p-value with a width that is approximately as wide as the p-value itself. Effectively, simulations are more precise for smaller p-values. The following example illustrates computation of simulation p-values with min.sim=1000.

# simulations when binary response
score.bin.sim <- haplo.score(y.bin, geno, trait.type = "binomial", x.adj = NA, locus.label = genolabel,
    min.count = 5, simulate = TRUE, sim.control = score.sim.control())
print(score.bin.sim)

---------------------------------------------------------------------------------------------------- 
                                  Haplotype Effect Model: additive                                   
---------------------------------------------------------------------------------------------------- 
---------------------------------------------------------------------------------------------------- 
                                      Global Score Statistics                                        
---------------------------------------------------------------------------------------------------- 

global-stat = 33.70125, df = 18, p-val = 0.01371

---------------------------------------------------------------------------------------------------- 
                                 Global Simulation p-value Results                                   
---------------------------------------------------------------------------------------------------- 

Global sim. p-val =  0.0095 
Max-Stat sim. p-val =  0.00563 
Number of Simulations, Global:  2842 , Max-Stat: 2842

---------------------------------------------------------------------------------------------------- 
                                     Haplotype-specific Scores                                       
---------------------------------------------------------------------------------------------------- 

      DQB DRB B  Hap-Freq Hap-Score p-val   sim p-val
 [1,] 62  2   7  0.05098  -2.19387  0.02824 0.02991  
 [2,] 51  1   35 0.03018  -1.58421  0.11315 0.13863  
 [3,] 63  13  7  0.01655  -1.56008  0.11874 0.19177  
 [4,] 21  7   7  0.01246  -1.47495  0.14023 0.15588  
 [5,] 32  4   7  0.01678  -1.00091  0.31687 0.25123  
 [6,] 32  4   62 0.02349  -0.6799   0.49657 0.47467  
 [7,] 51  1   27 0.01505  -0.66509  0.50599 0.63089  
 [8,] 31  11  35 0.01754  -0.5838   0.55936 0.6506   
 [9,] 31  11  51 0.01137  -0.43721  0.66196 0.91872  
[10,] 51  1   44 0.01731  0.00826   0.99341 1        
[11,] 32  4   60 0.0306   0.03181   0.97462 0.95074  
[12,] 62  2   44 0.01367  0.16582   0.8683  0.91872  
[13,] 63  13  44 0.01606  0.22059   0.82541 0.7266   
[14,] 63  2   7  0.01333  0.2982    0.76555 0.89163  
[15,] 62  2   18 0.01545  0.78854   0.43038 0.6608   
[16,] 21  7   44 0.02332  0.84562   0.39776 0.39796  
[17,] 31  4   44 0.02849  2.50767   0.01215 0.01161  
[18,] 21  3   8  0.10408  3.77763   0.00016 0.00035  

New and Updated Methods for haplo.glm

We initially wrote haplo.glm with a focus on creating a basic print method for results. We have now refined the haplo.glm class to look and act as much like a glm class object as possible with methods defined specifically for the haplo.glm class. We provide print and summary methods that make use of the corresponding methods for glm and then add extra information for the haplotypes and their frequencies. Furthermore, we have defined for the haplo.glm class some of the standard methods for regression fits, including residuals, fitted.values, vcov, and anova. We later describe the challenges that haplotype regression presents with these methods.

Preparing the data.frame for haplo.glm

A critical distinction between haplo.glm and all other functions in Haplo Stats is that the definition of the regression model follows the S/R formula standard (see lm or glm). So, a data.frame must be defined, and this object must contain the trait and other optional covariates, plus a special kind of genotype matrix (geno.glm for this example) that contains the genotypes of the marker loci. We require the genotype matrix to be prepared using setupGeno(), which handles character, numeric, or factor alleles, and keeps the columns of the genotype matrix as a single unit when inserting into (and extracting from) a data.frame. The setupGeno function recodes all missing genotype value codes given by miss.val to NA, and also recodes alleles to integer values. The original allele codes are preserved within an attribute of geno.glm, and are utilized within haplo.glm. The returned object has class model.matrix, and it can be included in a data.frame to be used in haplo.glm. In the example below we prepare a genotype matrix, geno.glm, and create a data.frame object, glm.data, for use in haplo.glm.

# set up data for haplo.glm, include geno.glm, covariates age and male, and responses resp and
# y.bin
geno <- hla.demo[, c(17, 18, 21:24)]
geno.glm <- setupGeno(geno, miss.val = c(0, NA), locus.label = genolabel)
attributes(geno.glm)

$dim
[1] 220   6

$dimnames
$dimnames[[1]]
NULL

$dimnames[[2]]
[1] "DQB.a1" "DQB.a2" "DRB.a1" "DRB.a2" "B.a1"   "B.a2"  


$class
[1] "model.matrix"

$unique.alleles
$unique.alleles[[1]]
 [1] "21" "31" "32" "33" "42" "51" "52" "53" "61" "62" "63" "64"

$unique.alleles[[2]]
 [1] "1"  "2"  "3"  "4"  "7"  "8"  "9"  "10" "11" "13" "14"

$unique.alleles[[3]]
 [1] "7"  "8"  "13" "14" "18" "27" "35" "37" "38" "39" "41" "42" "44" "45" "46" "47" "48" "49" "50"
[20] "51" "52" "55" "56" "57" "58" "60" "61" "62" "63" "70"

y.bin <- 1 * (hla.demo$resp.cat == "low")
glm.data <- data.frame(geno.glm, age = hla.demo$age, male = hla.demo$male, y = hla.demo$resp, y.bin = y.bin)

Rare Haplotypes

The issue of deciding which haplotypes to use for association is critical in haplo.glm. By default it will model a rare haplotype effect so that the effects of other haplotypes are in reference to the baseline effect of the one common happlotype. The rules for choosing haplotypes to be modeled in haplo.glm are similar to the rules in haplo.score: by a minimum frequency or a minimum expected count in the sample.

Two control parameters in haplo.glm.control may be used to control this setting: haplo.freq.min may be set to a selected minimum haplotype frequency, and haplo.min.count may be set to select the cut-off for minimum expected haplotype count in the sample. The default minimum frequency cut-off in haplo.glm is set to \(0.01\). More discussion on rare haplotypes is included later.

Regression for a Quantitative Trait

The following illustrates how to fit a regression of a quantitative trait y on the haplotypes estimated from the geno.glm matrix, and the covariate male. For na.action, we use na.geno.keep, which keeps a subject with missing values in the genotype matrix if they are not missing all alleles, but removes subjects with missing values (NA) in either the response or covariate.

# glm fit with haplotypes, additive gender covariate on gaussian response
fit.gaus <- haplo.glm(y ~ male + geno.glm, family = gaussian, data = glm.data, na.action = "na.geno.keep",
    locus.label = genolabel, x = TRUE, control = haplo.glm.control(haplo.freq.min = 0.02))

summary(fit.gaus)

Call:
haplo.glm(formula = y ~ male + geno.glm, family = gaussian, data = glm.data, 
    na.action = "na.geno.keep", locus.label = genolabel, control = haplo.glm.control(haplo.freq.min = 0.02), 
    x = TRUE)

Coefficients:
                  coef       se   t.stat  pval
(Intercept)    1.06436  0.34283  3.10464 0.002
male           0.09735  0.15521  0.62723 0.531
geno.glm.17    0.28022  0.43549  0.64346 0.521
geno.glm.34   -0.31713  0.34342 -0.92342 0.357
geno.glm.77    0.22167  0.36126  0.61360 0.540
geno.glm.78    1.14144  0.38382  2.97390 0.003
geno.glm.100   0.55557  0.36427  1.52517 0.129
geno.glm.138   0.98229  0.30329  3.23875 0.001
geno.glm.rare  0.39765  0.18191  2.18591 0.030

(Dispersion parameter for gaussian family taken to be 1.269581)

    Null deviance: 297.01  on 219  degrees of freedom
Residual deviance: 267.88  on 211  degrees of freedom
AIC: 687.65

Number of Fisher Scoring iterations: 268


Haplotypes:
              DQB DRB  B hap.freq
geno.glm.17    21   7 44  0.02291
geno.glm.34    31   4 44  0.02858
geno.glm.77    32   4 60  0.03022
geno.glm.78    32   4 62  0.02390
geno.glm.100   51   1 35  0.03008
geno.glm.138   62   2  7  0.05023
geno.glm.rare   *   *  *  0.71000
haplo.base     21   3  8  0.10409

The summary function for haplo.glm shows much the same information as summary for glm objects with the extra table for the haplotype frequencies. The above table for Coefficients lists the estimated regression coefficients (coef), standard errors (se), the corresponding t-statistics (t.stat), and p-values (pval). The labels for haplotype coefficients are a concatenation of the name of the genotype matrix (geno.glm) and unique haplotype codes assigned within haplo.glm. The haplotypes corresponding to these haplotype codes are listed in the Haplotypes table, along with the estimates of the haplotype frequencies (hap.freq). The rare haplotypes, those with expected counts less than haplo.min.count=5} (equivalent to having frequencies less than .01136 }) in the above example), are pooled into a single category labeled geno.glm.rare. The haplotype chosen as the baseline category for the design matrix (most frequent haplotype is the default) is labeled as *haplo.base}.

Fitting Haplotype x Covariate Interactions

Interactions are fit by the standard S-language model syntax, using a ‘\(*\)’ in the model formula to indicate main effects and interactions. Some other formula constructs are not supported, so use the formula parameter with caution. Below is an example of modeling the interaction of male and the haplotypes. Because more terms will be estimated in this case, we limit how many haplotypes will be included by increasing haplo.min.count to 10.

# glm fit haplotypes with covariate interaction
fit.inter <- haplo.glm(formula = y ~ male * geno.glm, family = gaussian, data = glm.data, na.action = "na.geno.keep",
    locus.label = genolabel, control = haplo.glm.control(haplo.min.count = 10))
summary(fit.inter)

Call:
haplo.glm(formula = y ~ male * geno.glm, family = gaussian, data = glm.data, 
    na.action = "na.geno.keep", locus.label = genolabel, control = haplo.glm.control(haplo.min.count = 10))

Coefficients:
                       coef       se   t.stat  pval
(Intercept)         0.97536  0.52268  1.86607 0.063
male                0.25806  0.67351  0.38315 0.702
geno.glm.17         0.14443  0.54544  0.26479 0.791
geno.glm.34        -0.17161  0.66773 -0.25700 0.797
geno.glm.77         0.80523  0.64951  1.23975 0.216
geno.glm.78         0.49557  0.56574  0.87596 0.382
geno.glm.100        0.52310  0.48067  1.08828 0.278
geno.glm.138        1.15704  0.42325  2.73371 0.007
geno.glm.rare       0.45547  0.28721  1.58587 0.114
male:geno.glm.17    0.50872  0.87531  0.58119 0.562
male:geno.glm.34   -0.28137  0.78570 -0.35812 0.721
male:geno.glm.77   -0.90084  0.79114 -1.13865 0.256
male:geno.glm.78    1.26376  0.77131  1.63846 0.103
male:geno.glm.100   0.05074  0.77470  0.06549 0.948
male:geno.glm.138  -0.44587  0.61903 -0.72027 0.472
male:geno.glm.rare -0.09787  0.37197 -0.26312 0.793

(Dispersion parameter for gaussian family taken to be 1.27362)

    Null deviance: 297.01  on 219  degrees of freedom
Residual deviance: 259.82  on 204  degrees of freedom
AIC: 694.93

Number of Fisher Scoring iterations: 120


Haplotypes:
              DQB DRB  B hap.freq
geno.glm.17    21   7 44  0.02346
geno.glm.34    31   4 44  0.02845
geno.glm.77    32   4 60  0.03060
geno.glm.78    32   4 62  0.02413
geno.glm.100   51   1 35  0.03013
geno.glm.138   62   2  7  0.05049
geno.glm.rare   *   *  *  0.70863
haplo.base     21   3  8  0.10410

The listed results similar as explained above. The main difference is that the interaction coefficients are labeled as a concatenation of the covariate (male in this example) and the name of the haplotype, as described above. In addition, estimates may differ because the model has changed.

Regression for a Binomial Trait

Next we illustrate the fitting of a binomial trait with the same genotype matrix and covariate.

# gender and haplotypes fit on binary response, return model matrix
fit.bin <- haplo.glm(y.bin ~ male + geno.glm, family = binomial, data = glm.data, na.action = "na.geno.keep",
    locus.label = genolabel, control = haplo.glm.control(haplo.min.count = 10))
summary(fit.bin)

Call:
haplo.glm(formula = y.bin ~ male + geno.glm, family = binomial, 
    data = glm.data, na.action = "na.geno.keep", locus.label = genolabel, 
    control = haplo.glm.control(haplo.min.count = 10))

Coefficients:
                 coef      se  t.stat  pval
(Intercept)    1.5457  0.6547  2.3610 0.019
male          -0.4802  0.3308 -1.4518 0.148
geno.glm.17   -0.7227  0.8011 -0.9022 0.368
geno.glm.34    0.3641  0.6798  0.5356 0.593
geno.glm.77   -0.9884  0.7328 -1.3489 0.179
geno.glm.78   -1.4093  0.8543 -1.6496 0.101
geno.glm.100  -2.5907  1.1278 -2.2971 0.023
geno.glm.138  -2.7156  0.8524 -3.1860 0.002
geno.glm.rare -1.2610  0.3537 -3.5647 0.000

(Dispersion parameter for binomial family taken to be 1)

    Null deviance: 263.50  on 219  degrees of freedom
Residual deviance: 233.46  on 211  degrees of freedom
AIC: 251.11

Number of Fisher Scoring iterations: 61


Haplotypes:
              DQB DRB  B hap.freq
geno.glm.17    21   7 44  0.02303
geno.glm.34    31   4 44  0.02843
geno.glm.77    32   4 60  0.03057
geno.glm.78    32   4 62  0.02354
geno.glm.100   51   1 35  0.02977
geno.glm.138   62   2  7  0.05181
geno.glm.rare   *   *  *  0.70880
haplo.base     21   3  8  0.10405

The underlying methods for haplo.glm are based on a prospective likelihood. Normally, this type of likelihood works well for case-control studies with standard covariates. For ambiguous haplotypes, however, one needs to be careful when interpreting the results from fitting haplo.glm to case-control data. Because cases are over-sampled, relative to the population prevalence (or incidence, for incident cases), haplotypes associated with disease will be over-represented in the case sample, and so estimates of haplotype frequencies will be biased. Positively associated haplotypes will have haplotype frequency estimates that are higher than the population haplotype frequency. To avoid this problem, one can weight each subject. The weights for the cases should be the population prevalence, and the weights for controls should be 1 (assuming the disease is rare in the population, and controls are representative of the general population). See Stram et al. 2003 for background on using weights, and see the help file for haplo.glm for how to implement weights.

The estimated regression coefficients for case-control studies can be biased by either a large amount of haplotype ambiguity and mis-specified weights, or by departures from Hardy-Weinberg Equilibrium of the haplotypes in the pool of cases and controls. Generally, the bias is small, but tends to be towards the null of no association. See Stram et al. 2003 and Epstein and Satten, 2003 for further details.

Control Parameters

Additional parameters are handled using control, which is a list of parameters providing additional functionality in haplo.glm. This list is set up by the function haplo.glm.control. See the help file (help(haplo.glm.control)) for a full list of control parameters, with details of their usage. Some of the options are described here.

Controlling Genetic Models: haplo.effect

The haplo.effect control parameter for haplo.glm instructs whether the haplotype effects are fit as additive, dominant, or recessive. That is, haplo.effect determines whether the covariate (\(x\)) coding of haplotypes follows the values in Table 1 for each effect type. Heterozygous means a subject has one copy of a particular haplotype, and homozygous means a subject has two copies of a particular haplotype. \ \ \ \

Note that in a recessive model, the haplotype effects are estimated only from subjects who are homozygous for a haplotype. Some of the haplotypes which meet the haplo.freq.min and haplo.count.min cut-offs may occur as homozygous in only a few of the subjects. As stated above, recessive models should be used when the region has multiple common haplotypes.

The default haplo.effect is additive, whereas the example below illustrates the fit of a dominant effect of haplotypes for the gaussian trait with the gender covariate.

# control dominant effect of haplotypes (haplo.effect) by using haplo.glm.control
fit.dom <- haplo.glm(y ~ male + geno.glm, family = gaussian, data = glm.data, na.action = "na.geno.keep",
    locus.label = genolabel, control = haplo.glm.control(haplo.effect = "dominant", haplo.min.count = 8))

summary(fit.dom)

Call:
haplo.glm(formula = y ~ male + geno.glm, family = gaussian, data = glm.data, 
    na.action = "na.geno.keep", locus.label = genolabel, control = haplo.glm.control(haplo.effect = "dominant", 
        haplo.min.count = 8))

Coefficients:
                  coef       se   t.stat  pval
(Intercept)    1.64935  0.37350  4.41593 0.000
male           0.07969  0.15726  0.50673 0.613
geno.glm.17   -0.06035  0.42317 -0.14262 0.887
geno.glm.34   -0.66499  0.36392 -1.82731 0.069
geno.glm.77   -0.07339  0.34665 -0.21171 0.833
geno.glm.78    0.85369  0.36421  2.34394 0.020
geno.glm.100   0.24697  0.34561  0.71458 0.476
geno.glm.138   0.67295  0.28163  2.38944 0.018
geno.glm.rare  0.11195  0.34006  0.32922 0.742

(Dispersion parameter for gaussian family taken to be 1.300586)

    Null deviance: 297.01  on 219  degrees of freedom
Residual deviance: 274.42  on 211  degrees of freedom
AIC: 692.96

Number of Fisher Scoring iterations: 91


Haplotypes:
              DQB DRB  B hap.freq
geno.glm.17    21   7 44  0.02297
geno.glm.34    31   4 44  0.02855
geno.glm.77    32   4 60  0.03019
geno.glm.78    32   4 62  0.02391
geno.glm.100   51   1 35  0.03003
geno.glm.138   62   2  7  0.05023
geno.glm.rare   *   *  *  0.71003
haplo.base     21   3  8  0.10408

# control baseline selection, perform the same exact run as fit.bin, but different baseline by
# using haplo.base chosen from haplo.common
fit.bin$haplo.common

[1]  17  34  77  78 100 138

fit.bin$haplo.freq.init[fit.bin$haplo.common]

[1] 0.02332031 0.02848720 0.03060053 0.02349463 0.03018431 0.05097906

fit.bin.base77 <- haplo.glm(y.bin ~ male + geno.glm, family = binomial, data = glm.data, na.action = "na.geno.keep",
    locus.label = genolabel, control = haplo.glm.control(haplo.base = 77, haplo.min.count = 8))
summary(fit.bin.base77)

Call:
haplo.glm(formula = y.bin ~ male + geno.glm, family = binomial, 
    data = glm.data, na.action = "na.geno.keep", locus.label = genolabel, 
    control = haplo.glm.control(haplo.base = 77, haplo.min.count = 8))

Coefficients:
                 coef      se  t.stat  pval
(Intercept)   -0.4311  1.3586 -0.3173 0.751
male          -0.4802  0.3308 -1.4518 0.148
geno.glm.4     0.9884  0.7328  1.3489 0.179
geno.glm.17    0.2657  1.0254  0.2591 0.796
geno.glm.34    1.3525  0.9223  1.4665 0.144
geno.glm.78   -0.4209  1.0430 -0.4035 0.687
geno.glm.100  -1.6023  1.3007 -1.2319 0.219
geno.glm.138  -1.7273  1.0321 -1.6736 0.096
geno.glm.rare -0.2726  0.6834 -0.3989 0.690

(Dispersion parameter for binomial family taken to be 1)

    Null deviance: 263.50  on 219  degrees of freedom
Residual deviance: 233.46  on 211  degrees of freedom
AIC: 251.11

Number of Fisher Scoring iterations: 61


Haplotypes:
              DQB DRB  B hap.freq
geno.glm.4     21   3  8  0.10405
geno.glm.17    21   7 44  0.02303
geno.glm.34    31   4 44  0.02843
geno.glm.78    32   4 62  0.02354
geno.glm.100   51   1 35  0.02977
geno.glm.138   62   2  7  0.05181
geno.glm.rare   *   *  *  0.70880
haplo.base     32   4 60  0.03057

glm.data$ybig <- glm.data$y * 50
fit.gausbig <- haplo.glm(formula = ybig ~ male + geno.glm, family = gaussian, data = glm.data, na.action = "na.geno.keep",
    locus.label = genolabel, control = haplo.glm.control(haplo.freq.min = 0.02), x = TRUE)

summary(fit.gausbig)

Call:
haplo.glm(formula = ybig ~ male + geno.glm, family = gaussian, 
    data = glm.data, na.action = "na.geno.keep", locus.label = genolabel, 
    control = haplo.glm.control(haplo.freq.min = 0.02), x = TRUE)

Coefficients:
                  coef       se   t.stat  pval
(Intercept)    53.2180   1.7343  30.6849 0.000
male            4.8675   6.0042   0.8107 0.418
geno.glm.17    14.0111   0.2579  54.3195 0.000
geno.glm.34   -15.8563   1.0033 -15.8044 0.000
geno.glm.77    11.0835   0.9978  11.1078 0.000
geno.glm.78    57.0720   0.3855 148.0436 0.000
geno.glm.100   27.7784   0.3228  86.0564 0.000
geno.glm.138   49.1143   1.0334  47.5256 0.000
geno.glm.rare  19.8824   3.4583   5.7493 0.000

(Dispersion parameter for gaussian family taken to be 3173.952)

    Null deviance: 742530  on 219  degrees of freedom
Residual deviance: 669704  on 211  degrees of freedom
AIC: 2408.9

Number of Fisher Scoring iterations: 268


Haplotypes:
              DQB DRB  B hap.freq
geno.glm.17    21   7 44  0.02291
geno.glm.34    31   4 44  0.02858
geno.glm.77    32   4 60  0.03022
geno.glm.78    32   4 62  0.02390
geno.glm.100   51   1 35  0.03008
geno.glm.138   62   2  7  0.05023
geno.glm.rare   *   *  *  0.71000
haplo.base     21   3  8  0.10409

fit.gausbig$rank.info

[1] 175

fit.gaus$rank.info

[1] 182

fit.gausbig.eps <- haplo.glm(formula = ybig ~ male + geno.glm, family = gaussian, data = glm.data, na.action = "na.geno.keep",
    locus.label = genolabel, control = haplo.glm.control(eps.svd = 1e-10, haplo.freq.min = 0.02), x = TRUE)

summary(fit.gausbig.eps)

Call:
haplo.glm(formula = ybig ~ male + geno.glm, family = gaussian, 
    data = glm.data, na.action = "na.geno.keep", locus.label = genolabel, 
    control = haplo.glm.control(eps.svd = 1e-10, haplo.freq.min = 0.02), 
    x = TRUE)

Coefficients:
                  coef       se   t.stat  pval
(Intercept)    53.2180  17.1414   3.1046 0.002
male            4.8675   7.7603   0.6272 0.531
geno.glm.17    14.0111  21.7745   0.6435 0.521
geno.glm.34   -15.8563  17.1712  -0.9234 0.357
geno.glm.77    11.0835  18.0631   0.6136 0.540
geno.glm.78    57.0720  19.1910   2.9739 0.003
geno.glm.100   27.7784  18.2133   1.5252 0.129
geno.glm.138   49.1143  15.1646   3.2387 0.001
geno.glm.rare  19.8824   9.0957   2.1859 0.030

(Dispersion parameter for gaussian family taken to be 3173.952)

    Null deviance: 742530  on 219  degrees of freedom
Residual deviance: 669704  on 211  degrees of freedom
AIC: 2408.9

Number of Fisher Scoring iterations: 268


Haplotypes:
              DQB DRB  B hap.freq
geno.glm.17    21   7 44  0.02291
geno.glm.34    31   4 44  0.02858
geno.glm.77    32   4 60  0.03022
geno.glm.78    32   4 62  0.02390
geno.glm.100   51   1 35  0.03008
geno.glm.138   62   2  7  0.05023
geno.glm.rare   *   *  *  0.71000
haplo.base     21   3  8  0.10409

fit.gausbig.eps$rank.info

[1] 182

## set haplo.freq.min and haplo.min.info to same value to show how the rare coefficient may be
## modeled but standard error estimate is not calculated because all haps are below haplo.min.info
## warning expected
fit.bin.rare02 <- haplo.glm(y.bin ~ geno.glm, family = binomial, data = glm.data, na.action = "na.geno.keep",
    locus.label = genolabel, control = haplo.glm.control(haplo.freq.min = 0.02, haplo.min.info = 0.02))
summary(fit.bin.rare02)

Warning in sqrt(object$var.mat[cbind(1:ncoef, 1:ncoef)]): NaNs produced

Call:
haplo.glm(formula = y.bin ~ geno.glm, family = binomial, data = glm.data, 
    na.action = "na.geno.keep", locus.label = genolabel, control = haplo.glm.control(haplo.freq.min = 0.02, 
        haplo.min.info = 0.02))

Coefficients:
                 coef      se  t.stat  pval
(Intercept)    1.2409  1.3238  0.9374 0.350
geno.glm.17   -0.6068  1.5630 -0.3882 0.698
geno.glm.34    0.3189  1.2678  0.2516 0.802
geno.glm.77   -1.0719  1.3666 -0.7844 0.434
geno.glm.78   -1.3593  4.3659 -0.3113 0.756
geno.glm.100  -2.3984  2.0878 -1.1487 0.252
geno.glm.138  -2.6096  1.5043 -1.7347 0.084
geno.glm.rare -1.2233     NaN     NaN   NaN

(Dispersion parameter for binomial family taken to be 1)

    Null deviance: 263.50  on 219  degrees of freedom
Residual deviance: 235.59  on 212  degrees of freedom
AIC: 251.24

Number of Fisher Scoring iterations: 71


Haplotypes:
              DQB DRB  B hap.freq
geno.glm.17    21   7 44  0.02302
geno.glm.34    31   4 44  0.02841
geno.glm.77    32   4 60  0.03058
geno.glm.78    32   4 62  0.02353
geno.glm.100   51   1 35  0.02980
geno.glm.138   62   2  7  0.05190
geno.glm.rare   *   *  *  0.70872
haplo.base     21   3  8  0.10403

fitted.values

A challenge when defining methods for haplo.glm is that we account for the ambiguity in a sample haplotype pair. To handle this in the glm framework, the response and non-haplotype covariates are expanded for each person with a posterior probability of the haplotype given their genotype as a weight.
The returned object from haplo.glm looks somewhat like a regular glm, but the model matrix, response, and thus the fitted values, are all expanded.
Users who want to work with the expanded versions of those items are welcome to access them from the returned object.

We now provide a method to get the fitted values for each person, fitted.haplo.glm. These collapsed fitted values are calculated by a weighted sum of the expanded fitted values for each person where the weights are the posterior probabilities of the sample expanded haplotype pairs.

residuals

The residuals within the haplo.glm object are also expanded for the haplotype pairs for subjects. We provide residuals.haplo.glm to get the collapsed deviance, pearson, working, and response residuals for each person. Because we have not implemented a predict method for haplo.glm, the method does not calculate partial residuals.

vcov

We provide vcov.haplo.glm as a method to get the variance-covariance matrix of model parameters in the haplo.glm object. Unlike the standard glm object, this matrix is computed and retained in the returned object. We do this because the model parameters are the model coefficients and the haplotype frequencies, and it is computationally-intensive to compute.

We show how to get the variance matrix for all the parameters and for only the model coefficients.

varmat <- vcov(fit.gaus)
dim(varmat)

[1] 182 182

varmat <- vcov(fit.gaus, freq = FALSE)
dim(varmat)

[1] 9 9

print(varmat, digits = 2)

              (Intercept)     male geno.glm.17 geno.glm.34 geno.glm.77 geno.glm.78 geno.glm.100
(Intercept)         0.118 -0.01513     -0.0674     -0.0544     -0.0526    -0.05123      -0.0595
male               -0.015  0.02409      0.0065     -0.0022     -0.0038     0.00082       0.0067
geno.glm.17        -0.067  0.00646      0.1897      0.0335      0.0206     0.03217       0.0370
geno.glm.34        -0.054 -0.00218      0.0335      0.1179      0.0226     0.02753       0.0298
geno.glm.77        -0.053 -0.00375      0.0206      0.0226      0.1305     0.02602       0.0204
geno.glm.78        -0.051  0.00082      0.0322      0.0275      0.0260     0.14732       0.0285
geno.glm.100       -0.059  0.00674      0.0370      0.0298      0.0204     0.02853       0.1327
geno.glm.138       -0.059  0.00362      0.0307      0.0254      0.0256     0.02195       0.0214
geno.glm.rare      -0.058  0.00142      0.0320      0.0283      0.0278     0.02478       0.0281
              geno.glm.138 geno.glm.rare
(Intercept)        -0.0587       -0.0583
male                0.0036        0.0014
geno.glm.17         0.0307        0.0320
geno.glm.34         0.0254        0.0283
geno.glm.77         0.0256        0.0278
geno.glm.78         0.0220        0.0248
geno.glm.100        0.0214        0.0281
geno.glm.138        0.0920        0.0288
geno.glm.rare       0.0288        0.0331

anova and Model Comparison

We use the anova.glm method as a framework for anova.haplo.glm to allow comparisons of model fits. We limit the model comparisons to multiple nested model fits, which requires that each model to be compared is either a haplo.glm or glm fitted object. We eliminate the functionality of testing sub-models of a single fit because removal of a single covariate would require re-fitting of the reduced model to get updated coefficient and haplotype frequency estimates with a maximized log-likelihood. We decided to simplify the usage and require that all models to be compared are fully fitted.

As with the anova.glm method, it is difficult to check for truly nested models, so we pass the responsibility on to the user. We discuss some of the requirements.

One type of two-model comparison is between models with haplotypes (expanded subjects) and a reduced model without haplotypes. We check for the same sample size in these models by comparing the collapsed sample size from a haplo.glm fit to the sample size from the glm fit, which we remind users is only a loose check of model comparability.

The other comparison of two models in anova.haplo.glm is to compare two models that contain the same genotypes, and inherently the same haplotypes. This is more tricky because a subject may not have the same expanded set of possible haplotype pairs across two fits of haplo.glm unless the same seed is set before both fits. Even if a seed is the same, the other effects that are different between the two models will affect the haplotype frequency estimates, and may still result in a different expansion of haplotype pairs per subject. Our check of the collapsed sample size for the two models still applies with the same pitfalls, but a better assurance of model comparability is to use the same seed.

In the haplo.glm fit we provide the likelihood ratio test of the null model against the full model, which is the most appropriate test available for haplo.glm objects, but it is difficult to compare the log-likeihood across two haplo.glm fits. Therefore, we remain consistent with glm model comparison proposed by McCullagh and Nelder, 1989, and use the difference in deviance to compare models. Furthermore, we restrict the asymptotic test for model comparison to be the \(\chi^{2}\) test for goodness of fit.

Below we show how to get the LRT from the fit.gaus result, then show how to compare some of the nested models fit above, including a regular glm fit of \(y \sim male\). The anova method requires the nested model to be given first, and any anova with a haplo.glm object should explicitly call anova.haplo.glm.

fit.gaus$lrt

$lrt
[1] 22.34062

$df
[1] 8

glmfit.gaus <- glm(y ~ male, family = "gaussian", data = glm.data)

anova.haplo.glm(glmfit.gaus, fit.gaus)

Analysis of Deviance Table

Model 1: y ~ male
Model 2: y ~ male + geno.glm
  Resid. Df Resid. Dev Df Deviance Pr(>Chi)   
1       218     297.00                        
2       211     267.88  7   29.114 0.001752 **
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

anova.haplo.glm(fit.gaus, fit.inter)

Analysis of Deviance Table

Model 1: y ~ male + geno.glm
Model 2: y ~ male * geno.glm
  Resid. Df Resid. Dev Df Deviance Pr(>Chi)
1       211     267.88                     
2       204     259.82  7   8.0631   0.5017

anova.haplo.glm(glmfit.gaus, fit.gaus, fit.inter)

Analysis of Deviance Table

Model 1: y ~ male
Model 2: y ~ male + geno.glm
Model 3: y ~ male * geno.glm
  Resid. Df Resid. Dev Df Deviance Pr(>Chi)   
1       218     297.00                        
2       211     267.88  7  29.1137 0.001804 **
3       204     259.82  7   8.0631 0.501696   
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Combine Score and Group Results: haplo.score.merge

When analyzing a qualitative trait, such as binary, it can be helpful to align the results from haplo.score with haplo.group. To do so, use the function haplo.score.merge, as illustrated in the following example:

# merge haplo.score and haplo.group results
merge.bin <- haplo.score.merge(score.bin, group.bin)
print(merge.bin, nlines = 10)

---------------------------------------------------------------------------------------------------- 
                        Haplotype Scores, p-values, and Frequencies By Group                         
---------------------------------------------------------------------------------------------------- 
   DQB DRB  B Hap.Score   p.val Hap.Freq y.bin.0 y.bin.1
1   62   2  7  -2.19387 0.02824  0.05098 0.06789 0.01587
2   51   1 35  -1.58421 0.11315  0.03018 0.03754 0.00907
3   63  13  7  -1.56008 0.11874  0.01655 0.02176      NA
4   21   7  7  -1.47495 0.14023  0.01246 0.01969      NA
5   32   4  7  -1.00091 0.31687  0.01678 0.02628 0.00794
6   32   4 62  -0.67990 0.49657  0.02349 0.01911      NA
7   51   1 27  -0.66509 0.50599  0.01505 0.01855 0.00907
8   31  11 35  -0.58380 0.55936  0.01754 0.01982 0.01587
9   31  11 51  -0.43721 0.66196  0.01137 0.01321      NA
10  51   1 44   0.00826 0.99341  0.01731 0.01595 0.00000

The first column is a row index, the next columns (3 in this example) illustrate the haplotype, the Hap.Score column is the score statistic and p.val the corresponding $ ^{2} $ p-value. Hap.Freq is the haplotype frequency for the total sample, and the remaining columns are the estimated haplotype frequencies for each of the group levels (y.bin in this example). The default print method only prints results for haplotypes appearing in the haplo.score output. To view all haplotypes, use the print option all.haps=TRUE, which prints all haplotypes from the haplo.group output. The output is ordered by the score statistic, but the order.by parameter can specify ordering by haplotypes or by haplotype frequencyies.

Case-Control Haplotype Analysis: haplo.cc

We provide haplo.cc to run and combine the results of haplo.score, haplo.group, and haplo.glm for case-control data. The function peforms a score test and a glm on the same haplotypes. The parameters that determine which haplotypes are used are haplo.min.count and haplo.freq.min,
which are set in the control parameter, as done for haplo.glm.

Below we run haplo.cc setting the minimum haplotype frequency at \(0.02\). The print results are shown, in addition to the names of the objects stored in the cc.hla result.

# demo haplo.cc where haplo.min.count is specified use geno, and this function prepares it for
# haplo.glm
y.bin <- 1 * (hla.demo$resp.cat == "low")
cc.hla <- haplo.cc(y = y.bin, geno = geno, locus.label = genolabel, control = haplo.glm.control(haplo.freq.min = 0.02))

print(cc.hla, nlines = 25, digits = 2)

---------------------------------------------------------------------------------------------------- 
                                      Global Score Statistics                                        
---------------------------------------------------------------------------------------------------- 
global-stat = 27, df = 7, p-val = 3e-04

---------------------------------------------------------------------------------------------------- 
                                   Counts for Cases and Controls                                     
---------------------------------------------------------------------------------------------------- 
control    case 
    157      63 

    DQB DRB  B Hap-Score   p-val pool.hf control.hf case.hf glm.eff OR.lower    OR OR.upper
188  62   2  7    -2.185 0.02892  0.0507     0.0682  0.0159     Eff    0.014 0.074     0.39
126  51   1 35    -1.584 0.11314  0.0302     0.0376  0.0089     Eff    0.010 0.092     0.81
98   32   4 62    -0.680 0.49658  0.0235     0.0255      NA     Eff    0.049 0.258     1.37
97   32   4 60     0.031 0.97559  0.0306     0.0316  0.0397     Eff    0.082 0.340     1.41
18   21   7 44     1.056 0.29102  0.0217     0.0174  0.0476     Eff    0.129 0.627     3.05
62   31   4 44     2.516 0.01185  0.0285     0.0147  0.0635     Eff    0.363 1.392     5.34
12   21   3  8     3.777 0.00016  0.1041     0.0697  0.1905    Base       NA 1.000       NA
1    21   1  8        NA      NA  0.0023     0.0033      NA       R    0.147 0.294     0.59
2    21  10  8        NA      NA  0.0018     0.0032      NA       R    0.147 0.294     0.59
3    21  13  8        NA      NA  0.0027         NA      NA       R    0.147 0.294     0.59
4    21   2 18        NA      NA  0.0023     0.0032      NA       R    0.147 0.294     0.59
5    21   2  7        NA      NA  0.0023     0.0032      NA       R    0.147 0.294     0.59
6    21   3 18        NA      NA  0.0046     0.0064      NA       R    0.147 0.294     0.59
7    21   3 35        NA      NA  0.0057     0.0064      NA       R    0.147 0.294     0.59
8    21   3 44        NA      NA  0.0038     0.0033  0.0159       R    0.147 0.294     0.59
9    21   3 49        NA      NA  0.0023         NA      NA       R    0.147 0.294     0.59
10   21   3 57        NA      NA  0.0023         NA      NA       R    0.147 0.294     0.59
11   21   3 70        NA      NA  0.0023         NA      NA       R    0.147 0.294     0.59
13   21   4 14        NA      NA      NA     0.0064      NA    <NA>       NA    NA       NA
14   21   4 62        NA      NA  0.0045     0.0064      NA       R    0.147 0.294     0.59
15   21   7 13        NA      NA  0.0108         NA  0.0238       R    0.147 0.294     0.59
16   21   7 18        NA      NA  0.0025         NA      NA       R    0.147 0.294     0.59
17   21   7 35        NA      NA  0.0023         NA  0.0079       R    0.147 0.294     0.59
19   21   7 45        NA      NA  0.0023     0.0032      NA       R    0.147 0.294     0.59
20   21   7 47        NA      NA      NA         NA  0.0079    <NA>       NA    NA       NA

names(cc.hla)

[1] "cc.df"        "group.count"  "score.lst"    "fit.lst"      "ci.prob"      "exclude.subj"

First, from the names function we see that cc.hla also contains score.lst and fit.lst, which are the haplo.score and haplo.glm objects, respectively. For the printed results of haplo.cc, first are the global statistics from haplo.score, followed by cell counts for cases and controls. The last portion of the output is a data frame containing combined results for individual haplotypes:

Significance levels are indicated by the p-values for the score statistics, and the odds ratio (OR) confidence intervals for the haplotype effects. Note that the Odds Ratios are effect sizes of haplotypes, assuming haplotype effects are multiplicative. Since this last table has many columns, lines are wrapped in the output in this manual. You can align wrapped lines by the haplotype code which appears on the far left. Alternatively, instruct the print function to only print digits significant digits, and set the width settings for output in your session using the options() function.

Score Tests on Sub-Haplotypes: haplo.score.slide

To evaluate the association of sub-haplotypes (subsets of alleles from the full haplotype) with a trait, the user can evaluate a “window” of alleles by haplo.score, and slide this window across the entire haplotype. This procedure is implemented by the function haplo.score.slide. To illustrate this method, we use all 11 loci in the demo data, hla.demo.

First, make the geno matrix and the locus labels for the 11 loci. Then use haplo.score.slide for a window of 3 loci (n.slide=3), which will slide along the haplotype for all 9 contiguous subsets of size 3, using the previously defined gaussian trait resp.

# haplo.score on 11 loci, slide on 3 consecutive loci at a time
geno.11 <- hla.demo[, -c(1:4)]
label.11 <- c("DPB", "DPA", "DMA", "DMB", "TAP1", "TAP2", "DQB", "DQA", "DRB", "B", "A")
score.slide.gaus <- haplo.score.slide(hla.demo$resp, geno.11, trait.type = "gaussian", n.slide = 3, min.count = 5,
    locus.label = label.11)
print(score.slide.gaus)

  start.loc score.global.p global.p.sim max.p.sim
1         1        0.21550           NA        NA
2         2        0.09366           NA        NA
3         3        0.39042           NA        NA
4         4        0.48771           NA        NA
5         5        0.13747           NA        NA
6         6        0.14925           NA        NA
7         7        0.11001           NA        NA
8         8        0.00996           NA        NA
9         9        0.04255           NA        NA

The first column is the row index of the nine calls to haplo.score, the second column is the number of the starting locus of the sub-haplotype, the third column is the global score statistic p-value for each call. The last two columns are the simulated p-values for the global and maximum score statistics, respectively. If you specify simulate=TRUE in the function call, the simulated p-values would be present.

# plot global p-values for sub-haplotypes from haplo.score.slide
plot.haplo.score.slide(score.slide.gaus)

Scanning Haplotypes Within a Fixed-Width Window: haplo.scan

Another method to search for a candidate locus within a genome region is haplo.scan, an implementation of the method proposed by Cheng et al. in 2005. This method searches for a region for which the haplotypes have the strongest association with a binary trait by sliding a window of fixed width over each marker locus, and then scans over all haplotype lengths within each window. This latter step, scanning over all possible haplotype lengths within a window, distinguishes haplo.scan from haplo.score.slide (which considers only the maximum haplotype length within a window). To account for unknown linkage phase, the function haplo.em is called prior to scanning, to create a list of haplotype pairs and posterior probabilities. To illustrate the scanning window, consider a 10-locus dataset. When placing a window of width 3 over locus 5, the possible haplotype lengths that contain locus 5 are three (loci 3-4-5, 4-5-6, and 5-6-7), two (loci 4-5 and 5-6) and one (locus 5). For each of these loci subsets a score statistic is computed, which is based on the difference between the mean vector of haplotype counts for cases and that for controls. The maximum of these score statistics, over all possible haplotype lengths within a window, is the locus-specific test statistic, or the locus scan statistic. The global test statistic is the maximum over all computed score statistics. To compute p-values, the case/control status is randomly permuted. Below we run haplo.scan on the 11-locus HLA dataset with a binary response and a window width of \(3\), but first we use the results of summaryGeno to choose subjects with less than \(50,000\) haplotype pairs to speed calculations with all \(11\) polymorphic loci with many missing alleles.

geno.11 <- hla.demo[, -c(1:4)]
y.bin <- 1 * (hla.demo$resp.cat == "low")
hla.summary <- summaryGeno(geno.11, miss.val = c(0, NA))

# track those subjects with too many possible haplotype pairs ( > 50,000)
many.haps <- (1:length(y.bin))[hla.summary[, 4] > 50000]

# For speed, or even just so it will finish, make y.bin and geno.scan for genotypes that don't have
# too many ambigous haplotypes
geno.scan <- geno.11[-many.haps, ]
y.scan <- y.bin[-many.haps]

# scan haplotypes for regions within width of 3 for each locus.  test statistic measures difference
# in haplotype counts in cases and controls p-values are simulated for each locus and the maximum
# statistic, we do 100 simuations here, should use default settings for analysis

scan.hla <- haplo.scan(y.scan, geno.scan, width = 3, sim.control = score.sim.control(min.sim = 100, max.sim = 100),
    em.control = haplo.em.control())

print(scan.hla)

  Call: 
haplo.scan(y = y.scan, geno = geno.scan, 
    width = 3, em.control = haplo.em.control(), 
    sim.control = score.sim.control(min.sim = 100, 
        max.sim = 100))

==================================================================================================== 
                              Locus Scan-statistic Simulated P-values                                
==================================================================================================== 
          loc-1 loc-2 loc-3 loc-4 loc-5 loc-6 loc-7 loc-8 loc-9 loc-10 loc-11
sim.p-val     0     0     0     0     0     0     0     0     0      0      0

      Loci with max scan statistic:   2 
 Max-Stat Simulated Global p-value:   0 
             Number of Simulations:   100 

In the output we report the simulated p-values for each locus test statistic. Additionally, we report the loci (or locus) which provided the maximum observed test statistic, and the Max-Stat Simulated Global p-value is the simulated p-value for that maximum statistic. We print the number of simulations, because they are performed until p-value precision criteria are met. We would typically allow simulations to run under default parameters rather than limiting to \(100\) by the control parameters.

Creating Haplotype Effect Columns: haplo.design

In some instances, the desired model for haplotype effects is not possible with the methods given in haplo.glm. Examples include modeling just one haplotype effect, or modeling an interaction of haplotypes from different chromosomes, or analyzing censored data. To circumvent these limitations, we provide a function called haplo.design, which will set up an expected haplotype design matrix from a haplo.em object, to create columns that can be used to model haplotype effects in other modeling functions.

The function haplo.design first creates a design marix for all pairs of haplotypes over all subjects, and then uses the posterior probabilities to create a weighted average contribution for each subject, so that the number of rows of the final design matrix is equal to the number of subjects. This is sometimes called the expectation-substitution method, as proposed by Zaykin et al.  2002, and using this haplotype design matrix in a regression model is asymptotically equivalent to the score statistics from haplo.score Xie and Stram 2005. Although this provides much flexibility, by using the design matrix in any type of regression model, the estimated regression parameters can be biased toward zero see Lin and Zeng, 2006 for concerns about the expectation-substitution method).

In the first example below, using default parameters, the returned data.frame contains a column for each haplotype that meets a minimum count in the sample min.count. The columns are named by the code they are assigned in haplo.em.

# create a matrix of haplotype effect columns from haplo.em result
hap.effect.frame <- haplo.design(save.em)

names(hap.effect.frame)

 [1] "hap.4"   "hap.13"  "hap.17"  "hap.34"  "hap.50"  "hap.55"  "hap.69"  "hap.77"  "hap.78" 
[10] "hap.99"  "hap.100" "hap.102" "hap.138" "hap.140" "hap.143" "hap.155" "hap.162" "hap.165"

hap.effect.frame[1:10, 1:8]

   hap.4    hap.13    hap.17 hap.34 hap.50 hap.55 hap.69 hap.77
1      0 0.0000000 0.0000000      0      0      0      0      0
2      0 0.1253234 0.8746766      0      0      0      0      0
3      0 0.0000000 0.0000000      0      0      0      0      0
4      0 0.2862131 0.7137869      0      0      0      0      0
5      0 0.0000000 0.0000000      0      0      1      0      0
6      1 0.0000000 1.0000000      0      0      0      0      0
7      0 0.0000000 0.0000000      0      0      0      0      0
8      0 0.0000000 0.0000000      0      0      0      0      0
9      0 0.0000000 0.0000000      0      0      0      0      0
10     0 0.0000000 0.0000000      0      0      0      0      0

Additionally, haplo.design gives the user flexibility to make a more specific design matrix with the following parameters:

This second example below creates columns for specific haplotype codes that were most interesting in score.gaus.add, haplotypes with alleles 21-3-8 and 62-2-7, corresponding to codes 4 and 138 in haplo.em, respectively. Assume we want to test their individual effects when they are coded with haplo.effect=‘’dominant’’.

# create haplotype effect cols for haps 4 and 138
hap4.hap138.frame <- haplo.design(save.em, hapcodes = c(4, 138), haplo.effect = "dominant")

hap4.hap138.frame[1:10, ]

   hap.4   hap.138
1      0 0.0000000
2      0 0.8746766
3      0 0.0000000
4      0 0.0000000
5      0 0.0000000
6      1 0.0000000
7      0 1.0000000
8      0 0.0000000
9      0 0.1358696
10     0 0.0000000

dat.glm <- data.frame(resp = hla.demo$resp, male = hla.demo$male, age = hla.demo$age, hap.4 = hap4.hap138.frame$hap.4,
    hap.138 = hap4.hap138.frame$hap.138)

glm.hap4.hap138 <- glm(resp ~ male + age + hap.4 + hap.138, family = "gaussian", data = dat.glm)
summary(glm.hap4.hap138)

Call:
glm(formula = resp ~ male + age + hap.4 + hap.138, family = "gaussian", 
    data = dat.glm)

Coefficients:
             Estimate Std. Error t value Pr(>|t|)    
(Intercept)  1.913834   0.229577   8.336 9.11e-15 ***
male         0.048588   0.155290   0.313   0.7547    
age         -0.002651   0.011695  -0.227   0.8209    
hap.4       -0.405530   0.195857  -2.071   0.0396 *  
hap.138      0.584480   0.261763   2.233   0.0266 *  
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

(Dispersion parameter for gaussian family taken to be 1.318277)

    Null deviance: 297.01  on 219  degrees of freedom
Residual deviance: 283.43  on 215  degrees of freedom
AIC: 692.07

Number of Fisher Scoring iterations: 2

License:

Copyright 2003 Mayo Foundation for Medical Education and Research.

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.\

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. \

You should have received a copy of the GNU General Public License along with this program; if not, write to \ Free Software Foundation, Inc. \ 59 Temple Place, Suite 330 \ Boston, MA 02111-1307 USA \

For other licensing arrangements, please contact Daniel J. Schaid.\ Daniel J. Schaid, Ph.D.\ Division of Biostatistics\ Harwick Building - Room 775\ Mayo Clinic\ 200 First St., SW\ Rochester, MN 55905\ phone: 507-284-0639\ fax:\   507-284-9542\ email: schaid@mayo.edu\

This research was supported by United States Public Health Services, National Institutes of Health; Contract grant numbers R01 DE13276, R01 GM 65450, N01 AI45240, and R01 2AI33144. The hla.demo data is kindly provided by Gregory A. Poland, M.D. and the Mayo Vaccine Research Group for illustration only, and may not be used for publication.

Counting Haplotype Pairs When Marker Phenotypes Have Missing Alleles

The following describes the process for counting the number of haplotype pairs that are consistent with a sample observed marker phenotypes, allowing for some loci with missing data. Note that we refer to marker phenotypes, but our algorithm is oriented towards typical markers that have a one-to-one correspondence with their genotypes. We first describe how to count when none of the loci have missing alleles, and then generalize to allow loci to have either one or two missing alleles. When there are no missing alleles, note that homozygous loci are not ambiguous with respect to the underlying haplotypes, because at these loci the underlying haplotypes will not differ if we interchange alleles between haplotypes. In contrast, heterozygous loci are ambiguous, because we do not know the haplotype origin of the distinguishable alleles (i.e., unknown linkage phase).
However, if there is only one heterozygous locus, then it does not matter if we interchange alleles, because the pair of haplotypes will be the same. In this situation, if parental origin of alleles were known, then interchanging alleles would switch parental origin of haplotypes, but not the composition of the haplotypes. Hence, ambiguity arises only when there are at least two heterozygous loci. For each heterozygous locus beyond the first one, the number of possible haplotypes increases by a factor of 2, because we interchange the two alleles at each heterozygous locus to create all possible pairs of haplotypes. Hence, the number of possible haplotype pairs can be expressed as \(2^{x}\), where \(x = H-1\), if \(H\) (the number of heterozygous loci) is at least 2, otherwise \(x = 0\).

Now consider a locus with missing alleles. The possible alleles at a given locus are considered to be those that are actually observed in the data. Let \(a_{i}\) denote the number of distinguishable alleles at the locus. To count the number of underlying haplotypes that are consistent with the observed and missing marker data, we need to enumerate all possible genotypes for the loci with missing data, and consider whether the imputed genotypes are heterozygous or homozygous.

To develop our method, first consider how to count the number of genotypes at a locus, say the \(i^{th}\) locus, when either one or two alleles are missing. This locus could have either a homozygous or heterozygous genotype, and both possibilities must be considered for our counting method. If the locus is considered as homozygous, and there is one allele missing, then there is only one possible genotype; if there are two alleles missing, then there are \(a_{i}\) possible genotypes. A function to perform this counting for homozygous loci is denoted \(f(a_{i})\). If the locus is considered as heterozygous, and there is one allele missing, then there are $ a_{i}-1$ possible genotypes; if there are two alleles missing, then there are \(\frac{a_{i}(a_{i}-1)}{2}\)  possible genotypes. A function to perform this counting for heterozygous loci is denoted \(g(a_{i})\) These functions and counts are summarized in Table A.1. \

Factors for when a locus having missing allele(s) is counted as homozygous(\(f()\)) or heterozygous(\(g()\))\

Now, to use these genotype counting functions to determine the number of possible haplotype pairs, first consider a simple case where only one locus, say the \(i^{th}\) locus, has two missing alleles. Suppose that the phenotype has H heterozygous loci (H is the count of heterozygous loci among those without missing data). We consider whether the locus with missing data is either homozygous or heterozygous, to give the count of possible haplotype pairs as

\[\begin{equation} a_{i}2^{x} + \left[{\frac{a_{i}(a_{i}-1)}{2}}\right]2^{x+1} \end{equation}\]

where again \(x = H-1\) if H is at least 2, otherwise x = 0. This special case can be represented by our more general genotype counting functions as

\[\begin{equation} f(a_{i})\,2^{x} + g(a_{i})\,2^{x+1} \end{equation}\]

When multiple loci have missing data, we need to sum over all possible combinations of heterozygous and homozygous genotypes for the incomplete loci. The rows of Table A.2 below present these combinations for up to \(m=3\) loci with missing data. Note that as the number of heterozygous loci increases (across the columns of Table A.2), so too does the exponent of 2. To calculate the total number of pairs of haplotypes, given observed and possibly missing genotypes, we need to sum the terms in Table A.2 across the appropriate row. For example, with \(m=3\), there are eight terms to sum over. The general formulation for this counting method can be expressed as \[\begin{equation} Total Pairs = \sum_{j=0}^{m} \sum_{combo} C(combo,j) \end{equation}\]

where combo is a particular pattern of heterozygous and homozygous loci among the loci with missing values (e.g., for \(m = 3\), one combination is the first locus heterozygous and the \(2^{nd}\) and \(3^{rd}\) third as homozygous), and \(C(combo,j)\) is the corresponding count for this pattern when there are \(i\) loci that are heterozygous (e.g., for \(m = 3\) and \(j = 1\), , as illustrated in Table A.2).