(Wang et al., 2013). Although the association did not replicate in the SAGE sample for this phenotype, there was a trend towards association with the other phenotype, ANYDEP (p=0.08). This weak replication for a different phenotype may be due to the fact that the majority of the SAGE sample was ascertained on nicotine and cocaine dependence, whereas the COGA sample was recruited based on an alcohol dependent proband and expanded to include the maximum number of alcohol dependent family members. The exclusion of nicotine dependence criteria may have attenuated the likelihood of replication, given ascertainment for nicotine dependence in SAGE. Since the SNP association was not primarily due to alcohol dependence, it is possible that high rates of comorbidity in the COGA sample as compared with the SAGE sample contributed to the finding. In addition, the family-based test in the large COGA families with comorbidity may have had greater power to detect the association. QUANTDEP seems to represent an underlying severity of addiction. As seen in Figure 3A, the higher the number of comorbid diagnoses, the higher the QUANTDEP scores.
