No association between dopamine D2 receptor gene (DRD2) and human intelligence

Significantly diminished intellectual functioning, as indicated by appropri ately administered IQ tests with scores below 70, is a frequent mental hand icap leading to severe social disadvantages and serves as a paradigm for mo lecular genetic research of complex disorders and traits due to its multitu de of known and unknown, genetic as well as environmental causes. Since the number of confounding variables is expected to be considerably reduced in the normal population at the opposite ends of the IQ distribution, we emplo yed a contrast of extremes approach by comparing adults of high (N = 71) an d average IQ (N = 78) in association studies to search for genes involved i n the multigenic forms of familial mental retardation. The dopamine D2 rece ptor gene (DRD2) was chosen as a candidate gene for general cognitive abili ty (g) since it has been found to be associated with visuospatial ability w hich in turn is highly correlated with g. Confirming two similar studies in children, however, no significant differences were obtained. Given three n egative studies, the DRD2 gene is unlikely to pay a major role in g.