The initial genome-wide association studies have taught us that very large sample sizes will be necessary to identify genes of small effect (Wellcome Trust Case Control Consortium, 2007), as are assumed involved in psychiatric and substance- use disorders. Failure to identify robust genetic effects reaching genome-wide significance has led to large-scale meta-analytic efforts (McMahon et al., 2010). But often, the increase in sample size comes with a reduction in phenotypic specificity, because different assessment measures or outcomes have been used across different samples. Rather than assuming that different measures are influenced by the same genetic factors, twin studies provide a method to explicitly evaluate these relationships. In this study, we examined the genetic architecture across different measures of current AC and problems in 2 independent twin samples from 2 different cultures: FT16 and the VATSPSUD. Previous analyses found a large proportion of overlap in the genetic factors that influence alcohol dependence and measures of AC during the heaviest period of drinking. Our analyses also suggest considerable overlap of genetic influences across different indices of current drinking and different measures of
