controls, providing evidence for an association with heroin dependence [68]. A study of DRD4 exon III VNTR polymorphisms in Israeli subjects found that the 4 and 7 repeats of exon III account for 90% of the alleles in an Israeli population, and the subjects possessing the 7-repeat allele demonstrated significantly higher levels of novelty seeking compared to subjects without this allele (F = 6.34, P = 0.013) [61]. Further studies of this gene as a risk factor for opioid dependence are therefore needed.
