Scientists have identified two genes linked to extremely violent behavior

A genetic analysis of almost 900 offenders in Finland has revealed two genes associated with violent crime. Those with the genes were 13 times more likely to have a history of repeated violent behavior. The authors of the study said that at least 5% to 10% of all violent crime in Finland could be attributed to individuals with these genotypes. The study, which involved analysis of almost 900 criminals, is the first to have looked at the genetic make-up of so many violent criminals in this way. Each criminal was given a profile based on their offenses, categorizing them into violent or non-violent. The association between genes and previous behavior was strongest for the 78 who fitted the extremely violent offender profile. This group had committed a total of 1,154 murders, manslaughters, attempted homicides or batteries. A replication group of 114 criminals had all committed at least one murder. These all carried a low-activity version of the MAOA gene, which previous research has dubbed the "warrior gene" because of its link to aggressive behavior. A deficiency of the enzyme this controls could result in "dopamine hyperactivity" especially when an individual drinks alcohol or takes drugs such as amphetamines, said Prof Tiihonen. The majority of all individuals who commit severe violent crime in Finland do so under the influence of alcohol or drugs. For now, a person's genetic information should not have any influence on conviction outcomes in criminal courts, Prof Tiihonen added. Commenting on the latest study, Dr Christopher Ferguson of Stetson University in Florida said that it added to our understanding of the factors involved in violent crime. "Studies like this really document that a large percentage of our behavior in terms of violence or aggression is influenced by our biology - our genes - and our brain anatomy. It's important to conceptualize crime and violence, where it comes from, even if we would not want to radically change the criminal justice system." The two genes associated with violent repeat offenders were the MAOA gene and a variant of cadherin 13 (CDH13). The MAOA gene codes for the enzyme monoamine oxidase A, which is important for controlling the amount of dopamine and serotonin in the brain. CDH13 has previously been associated with substance abuse and ADHD. Those classified as non-violent offenders did not have this genetic profile.