There are some limitations to the present study. Data on other Axis 1 diagnoses were not available for the patients. Since it is known that there is high comorbidity between substance dependence and other psychiatric disorders, particularly major depression, and the controls were free of all Axis 1 diagnoses, it is possible that the signals for association found in our study derived from hidden comorbidity. Nevertheless it should be noted that the extensive literature on association studies with GABRA2 (12–21) has largely focused on alcohol and drug dependence and no published study has yet shown a GABRA2 association with depression. Moreover, Covault et al’s 2004 (19) study showed that the association with alcoholism became stronger when alcoholics with major depression were removed.
