DNA was obtained from blood or lymphoblastoid cell lines, and genotyping was carried out on the Illumina Human IM Bead Chip by the Johns Hopkins University Center for Inherited Disease Research (CIDR). SNPs had a median missing call rate of less than 0.05%, and 95% of SNPs resulted in less than 1.4% missingness. Strict quality control procedures were implemented, including assessment of batch effects, duplication errors, gender and chromosomal anomalies, Hardy-Weinberg disequilibrium, hidden relatedness, Mendelian errors, missing call rates, and population structure (Laurie et al., 2010). Duplicates, outliers, and related subjects were removed. In total, 948,142 SNPs passed this thorough cleaning procedure (Bierut et al., 2010).
