Statistical analysis
Allele frequencies, genotype frequencies, and departures of genotype distributions from Hardy-Weinberg equilibrium (HWE) for each SNP were analyzed using chi-square test or Fisher's exact test. A p-value of <0.05 was considered statistically significant. Linkage disequilibrium (LD) was tested on pairwise combinations of polymorphisms using the absolute value of the standardized measure of LD, D', calculated by Haploview version 3.2. The haplotypes and their frequencies were estimated by Haploview version 3.2. Genotype-specific risks were estimated as odds ratios with associated 95% confidence intervals by unconditional logistic regression (SAS Institute Inc., Cary, NC, USA) and adjusted for age, gender, and smoking status.