All samples were genotyped using Illumina Human660W-Quad v1 DNA Analysis BeadChips at the Mayo Clinic. Quality control procedures were applied to each study using R, PLINK (Purcell et al., 2007) and EIGENSOFT (Patterson, Price & Reich, 2006). In each study, single nucleotide polymorphisms (SNPs) with missing rate>0.01, MAF<0.05, or extreme deviation (p<1E-6) from Hardy-Weinberg equilibrium were removed from further analysis. Subjects with missing rate>0.01 or unusual genome-wide homozygosity (|normalized homozygosity rate|>5) were excluded. Sex was investigated using no-call proportions of chr Y SNPs and heterozygosity proportions for chr X SNPs. Mislabeled sex information was corrected after double-checking the original data and subjects with unexplainable results were deleted. In addition, pairwise identical-by-descent (IBD) estimation was evaluated to identify unexpected duplicates and relative pairs. For VTSABD, one subject per twin-pair, selected at random, was retained in the current analysis.
