Hitherto, only a couple of workgroups have studied dopamine system related polymorphisms in BPD. The first genetic association study showing a dopaminergic effect on BPD was conducted among depressed patients [7]. The 9-repeat allele of the dopamine transporter gene (DAT1, SLC6A3) showed significant association with BPD, even when childhood abuse and neglect, and borderline temperament were included in the analyses. A recent study reported an over-representation of the low activity Met/Met genotype of the catechol-O-methyl-transferase (COMT) gene in 161 BPD patients [8]. Since COMT metabolizes catecholamines, these findings suggest that altered dopamine and/or norepinephrine neurotransmission might be a contributing factor in the development of BPD. In spite of the pharmacological evidence, dopamine D2 receptor (DRD2) polymorphisms have not been studied in relation to BPD. Dopamine D4 receptor (DRD4) might be another candidate, because of the preferential expression of this D2-family member in the prefrontal cortex [9] and its well-established role in ADHD [10] as well its possible involvement in human personality traits of novelty-seeking and impulsivity [11]. However, a pilot study of 39 BPD patients did not show any significant effect of DRD4 polymorphisms [12].
