Among the 7278 genotyped samples that passed all QC filters were 1127 samples from individuals with an MZ twin who had not been genotyped. The genotypes of the non-genotyped twins were set equal to the genotypes of their genotyped MZ cotwins, resulting in a final GWAS sample of 8405 individuals. The genotyped sample includes 3924 (47%) males and 4481 (53%) females; 4434 (53%) of the sample are in the offspring generation and 3971 (47%) are in the parent generation. In total, 2390 families are represented in the analysis. For purposes of analysis (see below), 4-member families were divided among MZ twin families (N=1156), DZ twin families (N=665), SIBS families with two adopted offspring (N=269), SIBS families with two biological offspring (N=191), and SIBS families with mixed adopted and biological offspring (N=109). In addition, there were 101 genotyped individuals, usually step parents, who did not fit into any one of these five 4-member family types. Table 2 provides an overview of the number of participants in each category. The family structure of the sample produces several unique features. In particular, it
