article_snippet.sent: In seeking to explain this connection, the researchers found that in only 2 per cent of cases could this familial connection be explained by shared environmental factors.
article_snippet.sent: On the other hand, their shared genetics were a factor in 40 per cent of cases, with the remaining 58 per cent of cases stemming from environmental factors not shared between family members.
article_snippet.sent: One of the genes examined was Monoamine oxidase A (MAOA).
article_snippet.sent: This gene is a key enzyme which breaks down and releases energy in brain neurotransmitters, such as serotonin.
article_snippet.sent: About 25 per cent of Caucasian men carry the less active variant of MAOA,' explained Professor Sheilagh Hodgins, a researcher at the University of Montreal. '