DRD3 polymorphism has been found to be associated with impulsivity. This association was significant in violent, but not in nonviolent individuals, and there were no association between DRD3 and violence per se (Retz et al., 2003). Dopamine transporter gene DAT1 has also been linked to ADHD (Waldman et al., 1998), as well as with violent behavior and delinquency in adolescents and young adults (Guo et al., 2008). Cateocholamine-O-methyl-transferase (COMT) has been examined primarily in children and adults with ADHD, and mixed evidence emerged for its association with conduct disorder and aggression (Caspi et al., 2008). Several studies have provided evidence that the low activity VNTR alleles of 5HTTLPR show associations with aggression, violence, aggressive symptoms of conduct disorder, and other forms of externalizing behavior (Haberstick et al., 2006b; Linnoila et al., 1983). Aggressive behavior has also shown associations with SNPs of epinephrine and norepinephrine. A recent study linked two SNPs of PNMT to cognitive and aggressive impulsivity in children and adolescents (Oades et al., 2008).
