Statistical analysis
Allele and genotype frequencies of each SNP were determined by direct counting. Genotype and allele frequencies between groups were compared using the χ2 test and Fisher’s exact test when appropriate. For allelic associations, p values with Yates correction and odds ratio (OR) with 95% confidence intervals (CI) were calculated using Statcalc program (Epiinfo version 6.0.4, CDC, Atlanta, GA). Pair-wise LD (D’, r2) was estimated by use of Haploview software version 4.2. Chi-square tests were performed for categorical data, while student’s t -test (or Mann Whitney U test when appropriate) were performed for comparison of continuous data. Differences in means with a significance value (p<0.05) were considered significant. Standard errors (and/or deviations) of treatment means were also calculated.