The Maoa Gene

Monoamine oxidase A, also known as MAO-A, is an enzyme that in humans is encoded by the MAO-A gene. Monoamine oxidase A is an enzyme that degrades amine
neurotransmitters, such as dopamine, norepinephrine, and serotonin. The protein localizes to the outer mitochondrial membrane. Its encoding gene is adjacent to a related gene (MAO-B) on the opposite strand of chromosome X. Mutation in this gene results in monoamine oxidase deficiency, or Brunner syndrome.
The maoa gene with deficiency in monoamine oxidase A, will result in the loss of neurotransmitters and in the big picture cause a loss of a conscious thought process in the brain. The lack of this enzyme in the gene is what most psychologists believe causes a brain of a serial killer.
The MAOA gene is located on the short (p) arm of the X chromosome at position 11.3.