Association study between the DAT1, DBH and DRD2 genes and cocaine dependence in a Spanish sample

Drug addiction is a complex neuropsychiatric disorder involving the environmental and genetic factors. Genetic and physiological evidences suggest that the dopaminergic system may play an important role in cocaine abuse and dependence. Several association studies have focused on dopaminergic genes. We genotyped the Int8 and 3'UTR variable number of tandem repeats of the dopamine transporter gene (DAT1/SLC6A3), the TaqIA (rs1800497) and TaqIB (rs1079597) SNP polymorphisms within the dopamine receptor D2 gene and the 19-bp insertion/deletion and c.444G>A (rs1108580) polymorphisms of the dopamine β-hydroxylase gene (DBH) in a Spanish sample of 169 patients with cocaine addiction and 169 sex-matched controls. The case-control study showed a nominal overrepresentation of the 5R/5R genotype of the Int8 variable number of tandem repeats within DAT1 in cocaine abusers (P=0.016). However, no significant associations were detected when DAT1 haplotype frequencies or polymorphisms within the other dopaminergic genes were considered. Sample size is limited and further studies should be performed in a larger cohort.