MAO-A genetics (monoamine oxidase A)

MAO-A (monoamine oxidase A) is an enzyme that breaks down the messengers serotonin, noradrenaline, adrenaline and dopamine as well as the dietary amine tyramine. Its gene lies on the X chromosome: men have one copy, women two. The test looks at variants that influence how much enzyme is produced; studies focus above all on a repeat variant in the gene's control region (MAOA-uVNTR). Which variant was determined is stated in the report. The sample is EDTA blood; as a genetic test, written consent is required. MAO-A is part of the “Depression genetics” analysis.

What MAO-A does in the body

MAO-A sits on the outer membrane of mitochondria – in nerve cells, in the gut lining, in the liver and in the placenta. The enzyme removes the amino group of monoamines and thereby inactivates them; this produces aldehydes, ammonia and hydrogen peroxide. Serotonin and noradrenaline are broken down mainly by MAO-A, while dopamine is shared between MAO-A and the related MAO-B. In the gut and liver, MAO-A intercepts tyramine from matured foods such as cheese before larger amounts reach the circulation. The enzyme needs FAD, the active form of vitamin B2, as a cofactor.

What does the MAO-A variant mean for serotonin breakdown?

The control region of the MAO-A gene contains a short section that is repeated a varying number of times. In cell studies, the gene with 3.5 or 4 repeats was read more strongly than with 3 repeats; the rarer forms with 2 and 5 repeats are less clear-cut. A more weakly read form means less enzyme: serotonin and noradrenaline are then broken down more slowly, while a more strongly read form speeds up breakdown. How strongly this affects the brain has not been clarified in humans – measurements of enzyme activity in the brains of healthy men found no clear difference between the forms. Because men have only one X chromosome, they show a single form; in women both copies act together.

What can be read from the MAO-A genotype?

The more weakly read form became known to the public as the “warrior gene” because early studies described links with impulsive behaviour, especially in combination with stressful childhood experiences. Later, larger studies produced inconsistent results; for individuals, the variant allows no statement about personality, behaviour or mood. This must be distinguished from complete MAO-A deficiency caused by rare severe gene changes (Brunner syndrome), which has been described in a few families and is not comparable with the common variants. How much serotonin, noradrenaline and dopamine is actually present is shown by the neurotransmitter analyses; the genotype adds the inherited enzyme make-up.

The interpretation is given in your report.