A primary GWAS meta-analysis was conducted on the GWAS1, GWAS2, GWAS2 FAM, and TIC datasets using the inverse-variance method in METAL (17). Heterogeneity was assessed with Cochran’s I2 statistics. The genomic control factor (λ) was calculated for each individual GWAS and for the overall meta-analysis using all SNPs with MAF>0.01 to identify residual population stratification or systematic technical artifact (Figure S2). GWAS summary statistics were subjected to linkage disequilibrium (LD) score regression (LDSC) analyses on high quality, common SNPs (INFO>0.9 and MAF>0.01) to examine the LDSC intercept as a more specific measure of inflation of the GWAS test statistic (18) due to residual artifact or stratification. The genome-wide significant threshold for the GWAS (19, 20) was set at p=5.0×10−8.
