Psychopathy, platelet MAO activity and criminality among former juvenile delinquents

Psychopathy-related personality traits as well as platelet monoamine oxidase (MAO) activity and criminality from the age of 15 years were studied in a group of 68 male former juvenile delinquents and 32 control subjects. The former juvenile delinquents registered for crime as adults were found to have higher Psychopathy Check List (PCL) scores and lower platelet MAO activity than either juvenile delinquents who were not registered criminals from the age of 15 years or non-criminal controls. Although PCL scores and platelet MAO activity were unrelated, a configural frequency analysis showed a significant interaction. Individuals with PCL scores, low platelet MAO activity and persistent criminal behaviour constituted a significant 'type'. Among the 27 former juvenile delinquents who developed persistent criminality, 21 subjects (78%) had PCL scores greater than 0 and low platelet MAO activity, while none of these persistent criminals were characterized by a combination of zero PCL score and high platelet MAO activity.