Family-based association studies of bipolar disorder with candidate genes involved in dopamine neurotransmission: DBH, DAT1, COMT, DRD2, DRD3 and DRD5.

The dopaminergic system has been implicated in the aetiology of mood disorders. We conducted family-based association studies for polymorphisms at three genes involved in the metabolism of dopamine: dopamine transporter (DAT1), dopamine-beta-hydroxylase (DBH) and catechol-O-methyl transferase (COMT); and three dopamine receptors: DRD2, DRD3 and DRD5. We used a sample of 122 parent-offspring trios of British Caucasian origin where the proband had bipolar disorder I (BPI), and analysed the results with the transmission/disequilibrium test (TDT) which is robust to hidden population stratification. No statistically significant differences were found between transmitted and not transmitted alleles for any of the polymorphisms studied.