SNP genotypes were checked for Mendelian consistency using the program SimWalk2 [24]. The estimates of the allele frequencies and their standard errors were obtained using SOLAR [25]. Specific SNPs were removed from analysis if they had call rates <95% (n = 6,596), were uncommon alleles in less than 5 participants (26,537), deviated from Hardy-Weinberg equilibrium (n = 0), or were monoallelic (n = 56,448). The number of SNPs that passed quality control and were included in the GWA analysis was 899,892.
