subset of the cases by a number of criteria: they were more likely to meet criteria for an illicit drug dependence diagnosis (77.1% vs. 51.5%, P <0.001), had a higher mean number of illicit drug dependence symptoms (12.10, SD = 10.10 in AD cases with CD/SUI; 6.53, SD = 7.74 in other AD cases; P <0.001), had a younger age of onset of AD (23.86, SD = 7.37 in AD cases with CD/SUI; 28.12, SD = 9.08 in other AD cases; P <0.001), were more likely to meet criteria for alcohol withdrawal (59.3% vs. 51.3%, P = 0.01), and had a slightly higher mean symptom count for alcohol dependence symptoms (5.72 vs. 5.27; P <0.001). Several of the previous reports of associated genes in the COGA sample have been driven by the more severe, comorbid AD individuals in the sample [Edenberg et al., 2006; Dick et al., 2007; Edenberg et al., 2007; Wetherill et al., 2008].
