DNA was extracted from peripheral blood using a commercial kit (PureGene™; Gentra, Minneapolis, MN). We genotyped rs4680 using the TaqMan method and primers (supplied as pre-validated SNP Assays on Demand, Applied Biosystems). The rs4680 genotyping was performed using ABI PRISM 7900 Sequence Detection System (Applied Biosystems). All samples were genotyped in duplicate. An ancestry informative marker (AIM) panel of 90 SNPs chosen by our group for their ability to differentiate between major continental populations was genotyped using the Illumina BeadXpress Reader with VeraCode assays and the manufacturer’s protocol (Illumina, Inc., San Diego, CA). Genotypes were called using BeadStudio software (Illumina, Inc., San Diego, CA).
