[Heredity and role of serotonin in aggressive impulsive behavior]

The idea that heredity could influence behaviour, including personality is very old. Until the early 1980s, the evidence for genetic influences on personality derived almost exclusively from twin studies. More recently, studies comparing twins raised together with those raised in different environment confirmed that about 40% of the observed personality variance can be attributable to genetic factors. Since complex behaviours, such as those underlying personality functioning, are likely to be influenced by many genes, a continuum of genetic risk underlying behavioural dimensions that extend from normal to abnormal behaviour has been hypothesized. Behaviours related to aggressive impulses regulation could delineate a biologically anchored model of dispositions to both normal and pathological functioning: these behaviours are identified in animal species where they are genetically transmitted, and a growing body of evidence suggests that disturbances in the regulation of aggressive impulses could belong to a behavioural dimension (disturbances of impulse control) linked to serotonin. Theorists involved in modelling personality according to psychobiologic basis agree with the idea of an inhibitory function of serotonin on impulsive behaviour and recognise that the way individuals control their impulses could underlie a basic psychobiological personality dimension. According to genotypes and to environmental factors, these serotonin mediated behaviours may be diversely expressed varying from minor personality peculiarities (characterised by impulsivity, hostility, irritability, psychopathic deviance, excessive violence or by more clear-cut personality dysfunctioning such as antisocial, borderline, narcissistic and histrionic personality traits or disorders) to major psychiatric disturbances (suicidal behaviour, overt aggressive behaviour, intermittent explosive disorder, pathological gambling, pyromania, bulimia and some type of substance or alcohol abuse). Finally, recent molecular genetic studies have demonstrated that genes encoding some key proteins involved in serotonin transmission could present some polymorphism in relation with impulsive-aggressive behaviours.