We attempted to address some of the problems that have riddled candidate gene studies by using a relatively large, ethnically homogeneous sample with severe AD. We genotyped a sufficient number of tSNPs to cover most of the variation within 10 DA system genes, including DRD1–D5, SLC18A2, SLC6A3, DDC, TH, and COMT. Our study not only tested for association with the categorical diagnosis of AD but also with quantitative alcohol-related traits, which give more power than dichotomous traits and provide additional clinical information beyond a binary phenotype. Within alcohol-dependent cases only, we tested for association with disinhibitory psychopathology, including symptoms for AD, ASPD, ADHD, CD, DD, and scores for NS. Additionally, we assessed for association with a disinhibitory factor score. While there is no direct genetic connection between childhood ADHD and alcohol abuse/dependence, we included it in our analysis because it loaded onto a single disinhibitory factor. Finally, we only reported findings that were significant after set-based permutation, which limits the possibility that any of our results are false positives.
