Monoamine oxidase A is an enzyme that breaks down neurotransmitters – chemical messengers involved in transmitting messages from the brain to the rest of the body. Dopamine, norephinephrine and epinephrine are few examples of such neurotransmitters. Dopamine controls sensations involved in pleasure and reward and epinephrine and norephinephrine influence the flight-or-fight response.
When MAOA levels are low, which is the case in warrior gene carriers, these neurotransmitters are not broken down as efficiently, accounting for the observed behavioural disorders.