A functionally deficient DRD2 variant [Ser311Cys] is not linked to alcoholism and substance abuse

Association studies with the DRD2 Taq1A marker have been variable in implicating DRD2 as a "Reward Deficiency Syndrome Gene" for alcoholism and substance abuse. Given that the Taq1A marker is not functionally significant, second-generation studies on the DRD2 receptor to identify functional variants and evaluate their effect on the phenotype are the logical step towards confirming and extending the DRD2 hypothesis. This article discusses the implications and process of progress made in these directions. The new findings are the description of structural variants in the D2 receptor, the demonstration that one of these, Ser311Cys, largely prevents signal transduction following receptor activation and the use of Ser311Cys in a large association and sib-pair linkage anlysis in an American Indian isolate. In this particular population, the Cys311 variant is far more abundant (0.16) than in Caucasians (0.03). Genotyping of Ser311Cys, the DRD2 intron 2 STR, and the Taq1A marker in 459 subjects, including 373 sib-pairs and 15 Cys311/Cys311 homozygous individuals, revealed no association to alcoholism, substance use disorders, or schizophrenia. The implication is that a DRD2 variant that dramatically impairs receptor function was not sufficient to significantly alter alcoholism vulnerability in a relatively large and also genetically and environmentally homogeneous sample.