Hagit Cohen

The long form of the dopamine D4 receptor (D4DR) exon III repeat polymorphism has been linked in some but not all studies to impulsive, extravagant and novelty-seeking personality traits that are prominent in affiliated behaviours such as attention deficit disorder and substance abuse. In particular, we have reported previously an increased frequency of the long seven-repeat D4DR exon III allele in a group of 141 opioid-dependent subjects compared to 110 control subjects. In order to further substantiate the role of D4DR in contributing to heroin addiction we have genotyped an additional, smaller cohort of opioid-dependent subjects. In this new group of 57 opioid-dependent subjects compared to an expanded group of 143 control subjects a significant difference was observed in overall genotype frequency (p = 0.04). An excess of the seven-repeat allele of the D4DR receptor gene was also observed compared to control subjects (p = 0.06). The frequency of the seven-repeat allele is 15.8% in the heroin addict population vs. 8.1% in the control group, conferring a relative risk of 2.07 (95% CI: 0.98-4.38). An association between two polymorphisms considered together (D4DR and dopamine D3 receptor) and treatment retention was observed (p = 0.02). In a subgroup of 38 opioid-dependent subjects, who were successfully administered the TPQ, higher Harm Avoidance (p < 0.001) and Novelty Seeking (NS3; extravagant vs. reserved, p < 0.001) scores were found. In contrast to some previous reports, no relationship was apparent between TPQ scores and treatment retention in this small group of opioid-dependent subjects.