HIBAG-package {HIBAG} | R Documentation

## HLA Genotype Imputation with Attribute Bagging

### Description

To impute HLA types from unphased SNP data using an attribute bagging method.

### Details

Package: | HIBAG
Type: | R/Bioconductor Package
License: | GPL version 3
Kernel Version: | v1.4

HIBAG is a state of the art software package for imputing HLA types using SNP data, and it uses the R statistical programming language. HIBAG is highly accurate, computationally tractable, and can be used by researchers with published parameter estimates instead of requiring access to large training sample datasets. It combines the concepts of attribute bagging, an ensemble classifier method, with haplotype inference for SNPs and HLA types. Attribute bagging is a technique which improves the accuracy and stability of classifier ensembles using bootstrap aggregating and random variable selection.

Features:
1) HIBAG can be used by researchers with published parameter estimates (http://www.biostat.washington.edu/~bsweir/HIBAG/) instead of requiring access to large training sample datasets.
2) A typical HIBAG parameter file contains only haplotype frequencies at different SNP subsets rather than individual training genotypes.
3) SNPs within the xMHC region (chromosome 6) are used for imputation.
4) HIBAG employs unphased genotypes of unrelated individuals as a training set.
5) HIBAG supports parallel computing with R.

### Author(s)

Xiuwen Zheng [aut, cre, cph] zhengx@u.washington.edu, Bruce S. Weir [ctb, ths] bsweir@u.washington.edu

### References

Zheng X, Shen J, Cox C, Wakefield J, Ehm M, Nelson M, Weir BS; HIBAG – HLA Genotype Imputation with Attribute Bagging. The Pharmacogenomics Journal. doi: 10.1038/tpj.2013.18. http://www.nature.com/tpj/journal/v14/n2/full/tpj201318a.html

### Examples

    # HLA_Type_Table data
    head(HLA_Type_Table)
    dim(HLA_Type_Table)  # 60 13

    # HapMap_CEU_Geno data
    summary(HapMap_CEU_Geno)

    ######################################################################

    # make a "hlaAlleleClass" object
    hla.id <- "A"
    hla <- hlaAllele(HLA_Type_Table$sample.id,
        H1 = HLA_Type_Table[, paste(hla.id, ".1", sep="")],
        H2 = HLA_Type_Table[, paste(hla.id, ".2", sep="")],
        locus=hla.id, assembly="hg19")

    # divide HLA types randomly
    set.seed(100)
    hlatab <- hlaSplitAllele(hla, train.prop=0.5)
    names(hlatab)
    # "training"   "validation"
    summary(hlatab$training)
    summary(hlatab$validation)

    # SNP predictors within the flanking region on each side
    region <- 500   # kb
    snpid <- hlaFlankingSNP(HapMap_CEU_Geno$snp.id, HapMap_CEU_Geno$snp.position,
        hla.id, region*1000, assembly="hg19")
    length(snpid)  # 275

    # training and validation genotypes
    train.geno <- hlaGenoSubset(HapMap_CEU_Geno,
        snp.sel=match(snpid, HapMap_CEU_Geno$snp.id),
        samp.sel=match(hlatab$training$value$sample.id,
        HapMap_CEU_Geno$sample.id))
    test.geno <- hlaGenoSubset(HapMap_CEU_Geno,
        samp.sel=match(hlatab$validation$value$sample.id,
        HapMap_CEU_Geno$sample.id))

    # train a HIBAG model
    set.seed(100)
    # please use "nclassifier=100" when you use HIBAG for real data
    model <- hlaAttrBagging(hlatab$training, train.geno, nclassifier=4,
        verbose.detail=TRUE)
    summary(model)

    # validation
    pred <- predict(model, test.geno)
    summary(pred)

    # compare
    (comp <- hlaCompareAllele(hlatab$validation, pred, allele.limit=model,
        call.threshold=0))
    (comp <- hlaCompareAllele(hlatab$validation, pred, allele.limit=model,
        call.threshold=0.5))

    # save the parameter file
    mobj <- hlaModelToObj(model)
    save(mobj, file="HIBAG_model.RData")
    save(test.geno, file="testgeno.RData")
    save(hlatab, file="HLASplit.RData")

    # Clear Workspace
    hlaClose(model)  # release all resources of model
    rm(list = ls())

    ######################################################################

    # NOW, load a HIBAG model from the parameter file
    mobj <- get(load("HIBAG_model.RData"))
    model <- hlaModelFromObj(mobj)

    # validation
    test.geno <- get(load("testgeno.RData"))
    hlatab <- get(load("HLASplit.RData"))

    pred <- predict(model, test.geno)
    # compare
    (comp <- hlaCompareAllele(hlatab$validation, pred, allele.limit=model,
        call.threshold=0.5))

    #########################################################################
    # import a PLINK BED file
    #
    bed.fn <- system.file("extdata", "HapMap_CEU.bed", package="HIBAG")
    fam.fn <- system.file("extdata", "HapMap_CEU.fam", package="HIBAG")
    bim.fn <- system.file("extdata", "HapMap_CEU.bim", package="HIBAG")
    hapmap.ceu <- hlaBED2Geno(bed.fn, fam.fn, bim.fn, assembly="hg19")

    #########################################################################
    # predict
    #
    pred <- predict(model, hapmap.ceu, type="response")
    head(pred$value)
    #   sample.id allele1 allele2      prob
    # 1   NA10859   01:01   03:01 0.9999992
    # 2   NA11882   01:01   29:02 1.0000000
    # ...

    # delete the temporary files
    unlink(c("HIBAG_model.RData", "testgeno.RData", "HLASplit.RData"), force=TRUE)

[Package HIBAG version 1.24.0 Index]