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The etiology of Asperger syndrome is essentially unknown, but abnormality of the dopamine system has been shown in clinically overlapping disorders. The present study was designed to investigate the presynaptic dopamine function in Asperger syndrome. Eight healthy, drug-free males with Asperger syndrome and five healthy male controls were examined with positron emission tomography using 6-[18F]fluoro-L-DOPA ([18F]FDOPA) as a tracer. In the Asperger syndrome group, the [18F]FDOPA influx (Ki) values were increased in the striatum, i.e. in the putamen and caudate nucleus and in the frontal cortex. The results indicate that the dopamine system is affected in subjects with Asperger syndrome. Partially similar results have also been obtained in schizophrenia, suggesting an overlap not only of the clinical features but also of pathogenesis.

Patients with autism and Asperger syndrome (AS) are impaired in mindreading and imitation skills. One possibility would be that their 'mirror neuron' system, which matches action execution and observation, does not function properly. To test this hypothesis we compared action-viewing related motor cortex functions in an AS group (one autistic and four AS subjects) and eight control subjects. In both groups viewing hand actions modified the neuromagnetic approximately 20 Hz oscillatory activity in the primary motor cortex to the same extent. Thus impaired mindreading and imitation skills found in AS and autism do not seem to result from dysfunction of the motor cortex part of the action execution/observation system.