The genes encoding<unk> -A and<unk> -B are located side-by-side on the short arm of the X chromosome, and have about 70% sequence similarity. Rare mutations in the gene are associated with Brunner syndrome. A study based on the Dunedin cohort concluded that maltreated children with a low-activity polymorphism in the promoter region of the<unk> -A gene were more likely to develop antisocial conduct disorders than maltreated children with the high-activity variant. Out of the 442 total males in the study (maltreated or not), 37% had the low activity variant. Of the 13 maltreated males with low<unk> -A activity, 11 had been assessed as exhibiting adolescent conduct disorder and 4 were convicted for violent offenses. The suggested mechanism for this effect is the decreased ability of those with low<unk> -A activity to quickly degrade norepinephrine, the synaptic neurotransmitter involved in sympathetic arousal and rage. This is argued to provide direct support for the idea that genetic susceptibility to disease is not determined at birth, but varies with exposure to environmental influences. However, most individuals with conduct disorder or convictions did not have low activity of<unk> -A; maltreatment was found to have caused stronger predisposition for antisocial behavior than differences in<unk> -A activity. The claim that an interaction between low<unk> -A activity and maltreatment would cause anti-social behavior has been criticized since the predisposition towards anti-social behavior could equally well have been caused by other genes inherited from abusive parents. A possible link between predisposition to novelty seeking and a genotype of the<unk> -A gene has been found. A particular variant (or genotype), dubbed "warrior gene" in the popular press, was over-represented in Māori. This supported earlier studies finding different proportions of variants in different ethnic groups. This is the case for many genetic variants, with 33% White/Non-Hispanic, 61% Asian/Pacific Islanders having the low-activity<unk> -A promoter variant.
Monoamine oxidase
Tyrosine hydroxylase
Catechol-O-methyltransferase
Phenylalanine hydroxylase
Glutamate dehydrogenase
Dopamine beta-hydroxylase
Aromatic L-amino acid decarboxylase
Flavin containing monooxygenase 1