DNA was extracted from immortalized cell lines or directly from blood or saliva. For the GWAS analysis, 5799 DNA samples of subjects interviewed using SSADDA were genotyped on the Illumina HumanOmni1-Quad v1.0 microarray (Illumina, San Diego, California) containing 988,306 autosomal SNPs. Genome-wide association study genotyping was conducted at the Center for Inherited Disease Research and the Yale Center for Genome Analysis. All DNA samples were assigned to one of the above two locations and were genotyped using the same type of chip. Single nucleotide polymorphism genotypes were called using GenomeStudio software V2011.1 and genotyping module version 1.8.4 (Illumina).
