Association of dopamine and opioid receptor genetic polymorphisms with response to methadone maintenance treatment

Genetic variations of the dopamine and opioid receptors could influence the response to methadone maintenance treatment (MMT). We included 238 MMT patients according to their response to treatment and methadone dosing, along with 217 subjects without substance dependence. All were genotyped for polymorphisms of the dopamine D 1, D 2, µ-opioid and δ-opioid receptor genes. Results: The polymorphisms of the µ-opioid ( 118A> G), δ-opioid ( 921T> C), dopamine D 1 (DdeI) and D 2 (TaqI A) receptor genes were not associated with response to MMT and methadone dosing, whereas an association was found with the dopamine D 2 receptor ( DRD2) 957C> T polymorphism. The 957CC carriers were more frequently non-responders to treatment (OR = 2.4; p = 0.02) and presented a fourfold shorter period of negative urine screening ( p = 0.02). No significant differences in allele frequencies were observed between the MMT patients and the control group, suggesting no association of the analyzed polymorphisms with opioid dependence. These results suggest that DRD2 genotype may contribute to the understanding of the interindividual variability to the response to MMT.