P3b amplitude is not reduced in abstinent alcoholics with a current MDD

In two studies of long-term abstinent alcoholics (LTAAs), we found that about 17% had a current major depressive disorder (MDD). We tested the hypothesis that LTAAs with a current MDD diagnosis do not exhibit the reduced P3b event-related potential amplitude endophenotype for alcoholism. This is consistent with the majority of LTAAs with a current MDD having developed alcohol dependence via self-medication of their MDD rather than their alcohol dependence arising from the alcoholism endophenotype. We revisited the P3b data from the two LTAAs studies, comparing LTAAs with a current MDD vs. LTAAs without a current MDD to each other and to non-substance abusing controls (NSACs). In northern California, 48 LTAAs and 48 non-substance abusing controls were studied, while in Honolulu, 105 LTAAs and 77 NSACs were studied. A total of 26 LTAAs had a current MDD (10 in California and 16 in Honolulu). The difference in P3b amplitude and latency (measured in targets-standards) in a 3-condition visual oddball paradigm was compared to MDD diagnoses gathered using the computerized Diagnostic Interview Schedule. Across both study sites, LTAAs without a current MDD (either with no lifetime MDD or a lifetime, but not current MDD) had lower P3b amplitudes than NSACs. In contrast, P3b amplitudes in LTAAs with a current MDD did not differ from controls. We conclude that alcohol dependence in LTAAs with a current MDD did not derive from the alcoholism endophenotype. This group may not exhibit the externalizing diathesis characterized by impulsive, disinhibited behavior and may have developed alcohol dependence via excessive drinking in an attempt to self-medicate their MDD. These results have major implications for targeted treatments of alcoholism and comorbid MDD.