A logistic regression approach was used in the performance of single marker association tests for autosomal SNPs. Correction for population stratification (PS) was performed using the first two principal components (PC) resulting from a PCA across independent autosomal markers (pair-wise r2<0.05 within a sliding window of 200 SNPs width, conformity of SNPs with HWE (p>0.01), and a minor allele frequency (MAF) >=0.05). These two PCs where included as covariates in the logistic regression model. For the conditional analysis of markers other than rs1789891, this SNP was included as an additional covariate in the regression model, using the allelic dosage of A alleles as a predictor.
