though the sample size was too small to produce accurate estimates for AA twins.11 Additive genetic factors contributed to age of first drink and problem alcohol use in both EA and AA twins.20 Estimates of genetic variance were greater for age of first drink in EA twins (eg, heritability of 44% in EA twins, 26% in AA twins), while genetic variance was stronger for problem alcohol use in AA twins (eg, heritability of 21% in EA twins, 41% in AA twins), though these estimates did not differ significantly.20 This is likely due to a lack of statistical power resulting from the small number of available AA twin pairs, which makes it impossible to precisely estimate genetic and environmental contributions to complex traits or test for differences across populations. The MOAFTS sample is the largest twin sample that has systematically studied alcohol use outcomes in AAs; however, because it is limited to female-only pairs it precludes studying how sex and race influence complex traits such as alcohol related behaviors.19,20 Recent efforts are underway to increase participation of AAs and populations other than EAs in twin registries such as the MATR.21 Additional efforts have focused on creating AA specific twin registries, such
