COGA families had the strongest association in individuals with more severe AD and comorbid cocaine dependence (Foroud et al., 2008). Furthermore, Agrawal et al. showed that GABRA2 is associated with AD only in individuals with comorbid drug dependence. When these individuals were removed from the analysis, no association remained (Agrawal et al., 2006). A future step in developing genetic risk models for AD would be to assess for prediction for different subtypes of AD.
