Genomic DNA was extracted from 15 ml of peripheral blood using standard protocols in all but a small number of cases where DNA was collected from saliva samples using Oragene DNA isolation kits (DNA Genotek, Ottawa, Ontario, Canada). All samples were genotyped on the Illumina Cyto12 array version 2-1 at the Yale Center for Genome Analysis, and called in GenomeStudio software V2011.1 using genotyping module version 1.8.4 yielding 299,140 single nucleotide polymorphisms (SNPs). From the original 600 participants, 569 samples were retained with call rates of at least 97% and SNPs were removed from analysis if not successfully genotyped in at least 85% of remaining individuals. A total of 247,725 SNPs were included in the final GWA. One percent of the most highly polymorphic SNPs were used to confirm reported pedigree structure in PREST (Sun et al. 2002), resulting in 116 pedigrees ranging in size from 2 to 27 individuals with an additional 100 individuals unrelated to anyone else in the sample. Mendelian errors, detected on the basis of unshared alleles with parents and likely resulting from miscalls in the
