The dopamine transporter (SLC6A3; DAT1; DAT) is a direct target of stimulant drugs and thus a logical candidate gene for studies or stimulant sensitivity. Polymorphisms in this gene have been extensively studied in relation to stimulant drug responses and susceptibility to ADHD (reviewed in Banaschewski et al. 2010). In particular, attention has focused on a 40 bp variable nucleotide tandem repeat (VNTR) located in the 3′-untranslated region (UTR) of the gene, with a range of 3–11 repeats. The two most common alleles have either 9, or more commonly, 10 repeats (Vandenbergh et al. 1992). The 10-repeat allele has been associated with both higher and lower expression of the dopamine transporter in the brain (Fuke et al. 2001; van de Giessen et al. 2009; Van Dyck et al. 2005). The evidence described below suggests that polymorphisms in SLC6A3 play an important role in responses to stimulant drugs, although the direction of the association is inconsistent across studies.
