Homozygosity at the dopamine D3 receptor gene is associated with opiate dependence

Anatomical, pharmacological and human post-mortem studies suggest the dopamine D-3 receptor (DRD3) gene as a candidate for drug dependence. We thus performed an association study of the Bal I polymorphism at the DRD3 gene, including 54 opiate addicts and 70 controls. Opiate addicts had a higher sensation-seeking score (on the Zuckerman scale) than controls (P = 0.001), particularly a subgroup (70%) who had a distinctly higher score, exceeding 24. There were no marked differences in genotypes between patients as a whole and controls. However, patients with a sensation-seeking score above 24 were more frequently homozygotes for both alleles than patients with a sensation-seeking score under 24 (P = 0.038) or controls (P = 0.034). Although obtained in a sample of limited size, these results suggest that the DRD3 gene may have a role in drug dependence susceptibility in individuals with high sensation-seeking scores. This hypothesis is consistent with the role of DRD3 in mediating responses to drugs of abuse in animals and the association of homozygosity at the Bal I polymorphism with drug abuse in schizophrenic patients (see companion article by Krebs et al).