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 allows us to confirm the genetic relationships of a large proportion of the sample, providing an additional level of QC screen not existing in most GWAS samples. For 6919 (82.3%) of the genotyped participants (not counting the 1127 non-genotyped MZ cotwins), we were able to confirm their relationship with at least one genetic relative in the sample (e.g., DZ twin, parent-offspring). Even though there are 2390 families represented in the GWAS sample, because of spouse pairs and adoptive families the maximum number of genetically unrelated individuals in the sample is 4706. There are 1631 genotyped spouse pairs and 1404 families where both genetic parents and at least one offspring have been genotyped.
