The DRD2 gene and the risk for alcohol dependence in bipolar patients

The high co-morbidity between bipolar disorder and alcohol dependence may have different explanations, one of them being the existence of common genetic factors for the two disorders. Several candidate genes may be involved but the genes acting in the dopaminergic pathway may be more specifically involved. We have thus tested the role of the gene encoding the D2 dopamine receptor (Taql Al allele) in the potentially shared vulnerability to alcohol dependence and bipolar disorder. One hundred and twenty-two French (for at least two generations) patients were recruited on the basis of hospital or outpatient files and were interviewed with the DIGS. The Al allele frequencies were compared between four groups, namely, with bipolar patients and co-morbid alcohol dependence (N = 21), with bipolar patients without alcohol morbidity (N = 31), with alcohol dependence without mood disorder (N = 35) and unaffected controls (N = 35). The Hardy Weinberg equilibrium for the DRD2 Taql Al genotypes was respected for the sample as a whole, and for each subsample. We observed that 42.9% of control subjects have at least one Al allele, a frequency which is not significantly different from the one observed in the affected sample as a whole (39.1%), neither from patients with alcohol dependence (37.1%), patients with bipolar disorder (48.4%) nor patients with alcohol dependence and bipolar disorder (28.6%). The regression analysis based on the three variables (bipolar disorder, alcohol dependence and interaction between these two disorders) does not explain the presence of the Al allele of the DRD2 gene. We thus found no evidence for a significant role of the Al allele of the D2 dopamine receptor gene in the specific association between bipolar disorder and alcohol dependence in our sample. (C) 2000 Editions scientifiques et medicales Elsevier SAS.