High-molecular-weight DNA was isolated from ethylenediaminetetraacetic acid anticoagulated whole blood samples obtained from all participants using the Puregene kit (Gentra Systems, Minneapolis, MN, USA). Samples were genotyped using the Illumina Human 610-Quad BeadChip; rs324420 data were extracted based on our a priori hypotheses, and no other polymorphisms were tested. Consistent with the manufacturer's protocol (Illumina, San Diego, CA, USA), approximately 200 ng of DNA was used to genotype each subject sample. A BeadArray scanner detected each specifically hybridized DNA that was fluorescently labeled by a single base extension reaction, which were then stained and imaged on an Illumina BeadArray Reader. Next, Illumina BeadStudio software produced SNP genotypes from fluorescent intensities using default cluster settings. The distribution of our observed genotypes (CC = 50, CA = 28 and AA = 3) did not deviate from Hardy–Weinberg equilibrium (χ2 = 0.145, P = 0.704).
