The brain-derived neurotrophic factor gene (BDNF) encodes a factor involved in neuronal growth and differentiation and contains a SNP in exon 2 that alters the amino acid sequence (rs6265, aka Val66Met). The most convincing results for this variant come from Asian populations, who have a minor allele frequency of 49% [25]. In Han Chinese individuals, the C allele of rs6265 was significantly associated with increased risk of opioid dependence in two independent samples from central China (case n = 487, control n = 492) and Taiwan (case n = 200, control n = 122) [32, 33]. A meta-analysis found that the C/C genotype was more common in heroin-dependent Asian subjects than in healthy controls (case n = 1172, control n = 1211) [34]. Genotype at rs6265 may also predict the age of onset of OUD, although conflicting results have been observed [32, 33, 35].
