200ng of genomic DNA from each sample was genotyped using the Illumina HumanOmniExpress BeadChip (Illumina Inc, CA, USA). Following scanning, Illumina GenomeStudio software was used for genotype calling and the data were exported as ped and map files. PLINK31 was used to remove samples with > 5% missing values, and SNPs with > 1% missing values, Hardy-Weinburg equilibrium P < 0.001, and a minor allele frequency of < 5%. Subsequently, SNPs were also filtered so that each of the three genotype groups with 0, 1, or 2 minor alleles (or two genotype groups in the case of rare SNPs with 0 or 1 minor allele) had a minimum of 5 observations.
