These Two Genes Are Linked to Murder
Scientists in Finland have identified two genes associated with severe violent behavior. They report their results in the journal Molecular Psychiatry.
The first candidate is monoamine oxidase A, or MAOA for short. MAOA is a key regulator of dopamine levels in the brain.
A multifaceted hormone, dopamine plays diverse roles within the human body. In the brain, it controls feelings of arousal, award, and motor control, among others.
The researchers specifically focused on a low-activity version of the MAOA gene. Previously termed the "warrior gene," it doesn't regulate dopamine as effectively. Prior studies have demonstrated that subjects with the "warrior gene" display higher levels of aggressive and antisocial behavior.
The second gene candidate is a variant of T-cadherin, or CDH13, which specifically codes for a protein that affects the cell linings of neurons. CDH13 is already thought to be the most important genetic contributor to attention-deficit hyperactivity disorder. The association suggests a link to impulsive behavior.
The Finnish scientists gleaned the results from a group of 753 inmates incarcerated in Finland's 19 largest prisons. The group comprised 215 non-violent offenders, in jail for offenses like drunk-driving or drug distribution, and 538 violent offenders, who committed at least one act of murder, attempted murder, manslaughter, attempted manslaughter, or battery. Violent offenders who committed more than ten crimes were further classified into an "extremely violent" subgroup. 84 of them fit the bill.
Genetic testing showed that members of this extremely violent subgroup were much more likely than non-violent criminals to have the low-activity MAOA gene and the CDH13 variant.
Despite the strong results, the researchers make clear that the genetics of criminal behavior is a young science. It's far too early to even consider screening individuals for potential violent inclinations, nor should somebody's genotype be considered in the courtroom.
Though people with the low-activity MAOA gene and the CDH13 variant may be more likely to commit a violent crime, violent crime itself is a rare act, so the chance that they will commit one is still remote. The researchers conservatively estimate that 5–10% of all severe violent crime in Finland is attributable to the two genes.
Source: J Tiihonen et. al. "Genetic background of extreme violent behavior." Molecular Psychiatry (2014), 1–7