Monoamine Oxidase Activity and Tri-Iodothyronine Level in Violent Offenders with Early Behavioural Problems

The focus is on evaluating the relationships between early behavioural problems and biochemical variables at adult age and their significance for early criminality and violent behaviour in a life perspective. In the present study, using prospective longitudinal data, a sample of males with a history of early criminal behaviour and male controls (n = 103) were investigated concerning (1) teacher-rated behaviours at age 11–14 years; (2) platelet monoamine oxidase (MAO) activity and tri-iodothyronine (T 3 ) level at adult age; (3) registered early criminality (11–14 years); (4) records of violent offending up to age 35 years, and (5) interview data on smoking. The main finding was that a combined risk level pattern of low MAO activity and high T 3 level was found significantly more frequently than expected in violent offenders with an early behavioural risk pattern. Furthermore, there was a significant interaction effect between early attention difficulties and smoking on MAO activity, as well as an effect by smoking on MAO activity. The findings are discussed in terms of the possible influence of biological vulnerability to certain behaviours, which in combination with possible childhood stress, enhance the risk for antisocial behaviours and subsequent violence.