If you're not familiar with MAO-A here's some info-
"Recent years have seen huge advancements in DNA research, with researchers now able to identify specific genes that are linked to anti-social or aggressive behaviour, in particular the MAO-A gene (nicknamed “the warrior gene”), which appears to be hereditary.
A study of Danish twins concluded that a Danish man who has an identical twin with a criminal record is about 50 per cent more likely to have been in prison himself than the average Danish male. Non-identical twins are between 15 and 30 per cent more likely to both have criminal records. Similarly, adoption studies around the world have shown that a child of criminal parents is more likely to become a criminal, even if the adoptive parents are law-abiding.
Universities, law schools and, increasingly, the judicial system are all reviewing cases where it seems “the brain” rather than “the person” might be culpable. In the US, several killers have been sentenced for manslaughter rather than murder after DNA evidence was produced to show the perpetrator had unusually high levels of MAO-A. In Italy, in 2009, a judge reduced the sentence of an Algerian called Abdelmalek Bayout for the same reason. Bayout had stabbed a man to death in the northern city of Udine after a comment about his appearance."