Association analysis of polymorphisms in the DRD4 gene and heroin abuse in Chinese subjects.

Heroin abuse is a major social and public health problem in many parts of the world, yet relatively little is known about its etiology. Although genes play a role in determining susceptibility, they are expected to be of small effect with considerable heterogeneity. Because the dopamine system is involved in reward, its neurotransmitter receptors are candidates for etiological involvement in addiction. In the present study, we examine two polymorphisms in the dopamine D4 receptor, a VNTR in exon III and a point mutation in the promoter (-512C/T) that affects transcriptional efficiency. We examined a sample of 405 heroin-abusing subjects and 304 controls from Sichuan Province, Southwest China. One hundred twenty-one of these cases and 154 controls were previously used in a study of the DRD4 VNTR [Li et al., 1997], and the remainder are newly ascertained. The two polymorphisms were in weak but detectable linkage disequilibrium (1, 418 chromosomes, P < 0.00001, D' = 0.17). When we compared the heroin-abuse group with controls, we found no significant difference between the patients and controls for either polymorphism in the DRD4 gene or their haplotypes. We were also unable to replicate our earlier association between "long" DRD4 alleles and heroin abuse. However, division of the sample by route of administration (nasal inhalers or injectors) produced a significant difference between inhalers and controls for the DRD4 VNTR (six-fold corrected P = 0. 018 by allele) but not for injectors of heroin. The association we observed between inhalers and the DRD4 polymorphism is difficult to interpret, although it is possible that the association is explained by different levels of novelty seeking between the two subgroups.