In most cases DNA was obtained from immortalized cell lines, although for some subjects DNA was extracted directly from blood or saliva. Single nucleotide polymorphisms (SNPs) were genotyped at the Center for Inherited Disease Research (CIDR) using the Illumina Linkage IVb Marker Panel with SNP markers with average 0.64 cM spacing and an average marker heterozygosity of 0.38 in African Americans (http://www.cidr.jhmi.edu/human_snp.html). We previously reported association analyses with this dataset for the major substance dependence traits (29).
