Le Foll and colleagues’ (2009) review notes that certain variants in DRD3–D5 confer an increased risk of heroin dependence, while research on psychostimulant dependence has either been negative or inconclusive. A recent meta-analysis examining ADHD reported significant associations with variants in both DRD4 and DRD5, whereas there was no association with DRD3 (Gizer et al., 2009). Additionally, Kim and colleagues (2007) identified variants in DRD1 that increase scores for the disinhibitory personality trait NS in alcohol-dependent subjects. Of all DA genes, DRD4 has been the best studied for its role in NS. Munafò and colleagues’ (2008) meta-analysis identified association with C521T (rs1800955) but not with DRD4's 48-bp VNTR.
