The C_11975323_20 (T1880C) SNP genotyping kit was obtained from Applied Biosystems. The kit contained two flanking primers as well as C- and T-specific probes labeled with VIC and FAM fluorescent dyes, respectively. Genotyping reactions contained 1× TaqMan® PCR Master Mix, No AmpErase® UNG, and approximately 5 ng of genomic DNA in a final volume of 5 μL. Amplifications were performed using a 7300 Real-Time PCR System and the following thermocycling conditions: initial denaturation and activation at 95°C for 10 minutes, followed by 40 cycles of 95°C for 15 seconds and 60°C for 1 minute. The genotypes C602A and T1559C were detected using the SNP kits C_11975332_10 and C_8919523_1 (Applied Biosystems) following the instructions supplied by the manufacturer.