For all tests, ancestry-informative principal components were included as covariates.24 Each SNP was tested for all subjects, and then separately for males and for females. For the primary analysis of all subjects, a reasonable threshold for 5% genome-wide significance is a nominal P-value less than 5 × 10−8, based on three estimates assuming that all common SNPs have been directly or indirectly tested.31–33 The analyses of male and of female subjects were considered exploratory.
