Two SNP heritability studies have been performed for AD. McGue et al. (2013) used data from a GWAS that yielded no GWS associations to estimate SNP heritability with GCTA. Restricting their analysis to subjects with a genetic relatedness < 0.025, they found an estimate of 8% for AD. In the same sample, Vrieze et al. (2013) investigated genetic influences on behavioral disinhibition, AD, and alcohol consumption factor scores using both SNP heritability and profile scoring methods (discussed below). To address confounding by shared environment and non-SNP genetic influences, these investigators performed four separate GCTA analyses. Analysis in the full sample (n=7,188) yielded estimates very similar to those obtained using biometric methods in the subsample of twins (n= 2,877), likely reflecting shared environmental and non-additive, non-SNP genetic influences. The estimates in the unrelated parent sample (n=3,542) were 16% for AD and 18% for alcohol consumption; only the latter estimate was statistically significant. In the unrelated offspring sample (n=1,784), the estimates were unstable and non-significant, most likely due to the small sample. Estimates in the full offspring sample (n=3,336) were the highest of all, potentially reflecting greater shared environmental influences than obtained in the full sample including parents.
