In the present study, the -48A/G polymorphism of the DRD1 gene was estimated in patients with schizophrenia (n=407) or bipolar affective disorder (n=380), and in healthy controls (n=399).
Allele frequencies were similar in patients and controls, indicating that genetic variation in the 5'-regulatory region of the DRD1 gene is unlikely to play a frequent, major role in the genetic predisposition to either schizophrenia or bipolar affective disorder.
As the D1 dopamine receptor gene (DRD1) maps to this region and as alterations in dopaminergic neurotransmission have been indirectly implicated in the pathogenesis of MDI, we directly searched for mutations in the coding region of the DRD1 gene in 22 unrelated cases of bipolar I (BPI) disorder derived from multiplex families.