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Background: A Swedish male criminal population was grouped into personality disorder subgroups and investigated with regard to personality traits and platelet monoamine oxidase (MAO) activity. The main aim of the study was to examine the possibility of a risk factor combination by having low platelet MAO activity as well as belonging to a certain diagnostic DSM-IV axis I (drug abuse in the present series) and/or II subgroup. Methods: Personality disorders were grouped into clusters according to the cluster system used in DSM-IV axis II. The prisoners were grouped into five subgroups and each subject completed the Karolinska Scales of Personality self-report questionnaire. The comparison group for the personality data comprised 51 non-criminal males from a longitudinal Swedish project. Platelet MAO activity was assessed for the criminals as well as for a control group including 60 non-criminal healthy male Caucasians. For testing the existence of syndromes, a configuration frequency analysis (CFA) was used. Results: The results showed low scores on the socialisation and high scores on the sensation seeking-related traits impulsiveness and monotony avoidance, and the somatic anxiety-related muscular tension in the criminals with any DSM-IV mental disorder, however most markedly in cluster AB and cluster B subjects. In addition, cluster AB subjects had significantly lower platelet MAO activity than controls. Two significant ‘types’ were found among the criminals: one was characterised by low platelet MAO activity, cluster B personality diagnosis as well as drug abuse disorder diagnosis; and the other by a pattern of normal platelet MAO activity, no cluster B personality disorder and no drug abuse disorder diagnosis. Conclusion: The aggregation of certain risk factors in the same individual has been shown to contribute to the development of criminal behaviour.

Studies have shown that genetic components to some extent underlie behavioral disorders such as impulsive aggression and violence, and that central serotonergic mechanisms are involved in the development of such behavior. In the present study, we analyzed a polymorphism in the gene encoding the serotonin 2A receptor (5-HT2A -1438 G/A) in a group of Swedish criminals (n=97) and in a group of healthy Swedish blood donors (n=202). The 5-HT2A -1438 GG genotype was lower in the criminal group than in the control group (P=0.034). In accordance with previous results, no associations were found between the 5-HT2A -1438 G/A polymorphism and personality as measured by Karolinska Scales of Personality. Neither were there any associations between the studied polymorphism and the type of crime committed.

The study describes personality traits and the presence of personality disorders and mental disorders in a consecutive series of 130 male prisoners in Swedish jails sentenced for serious criminality. The investigation included a psychiatric examination by means of the Structured Clinical Interview (SCID) as well as information taken from criminal records. Personality assessments were made by means of self-report questionnaires, the Karolinska Scales of Personality (KSP) and the DSM-IV and ICD-10 Personality Disorder Questionnaire (DIP-Q). The most common mental disorders were alcohol and drug abuse/dependence, which were present in 55% of the subjects. Personality disorders, too, were common, being present in 56% of the subjects. In the KSP, high scores were found in scales related to impulsiveness, sensation-seeking, nervous tension and distress, cognitive-social anxiety, hostility and aggression. Very low scores were found in the Socialization scale, reflecting a high degree of psychopathy-related personality traits. Despite the high morbidity, the global level of functioning was unexpectedly high, 66 according to GAF. The male prisoners sentenced for heavy criminality had a high degree of both mental disorders and personality disorders. Furthermore, psychopathy-related personality traits were common.