The phenotype considered in this study is a count of the number of alcohol dependence (AD) symptoms as measured by the Diagnostic and Statistical Manual of Mental Disorders version 4 (DSM-IV). For both samples, the AD symptoms were assessed by in-person interviews. In the VTSABD, the DSM-IV was assessed when the subjects were 18 to 31 years old. The MTFS sample was assessed on AD at multiple time points, but to be comparable to VTSABD, only measures from when the subjects were 18 to 31 years old were used. Longitudinal measures, if available, were collapsed across subject by taking the maximum count of AD symptoms endorsed between 18 and 31 years of age. The age at which this maximum occurred was used as a covariate in the analyses. AD symptom count was treated as a quantitative trait in the following analyses.
