Monoamine oxidase A (MAOA) degrades monoamine neurotransmitters and has been most commonly associated with aggressive behavior (reviewed in Grigorenko et al. 2010). MAOA contains a 30 bp VNTR polymorphism within its promoter that consists of 3, 3.5, 4, or 5 repeats (MAOA-u VNTR); the 3.5 and 4 repeat alleles are transcribed more efficiently than the 3- or 5-repeat alleles (Sabol et al. 1998). Nakamura et al. (2009) tested the MAOA-u VNTR polymorphism for association with methamphetamine-induced psychosis, and found that in males, the 4-repeat allele was associated with having prolonged psychosis rather than transient; this effect was not seen in females.
