GWAS of psychiatric disorders contain a mixture of different signals. Moving beyond univariate to multivariate GWAS designs offers the potential to tease apart these signals. Herein, we decomposed the genetic variation of problematic alcohol use into that which is shared with other externalizing phenotypes from that which is specific to problematic alcohol use. Comparison of results at multiple levels showed that variance specific to problematic alcohol use was related to alcohol phenotypes while that which was shared was more strongly related to other forms of substance use and impulsivity. Differentiating these pathways of risk will become more important as genetic data becomes incorporated into clinical practice.
