Sex differences in the hyperkinetic syndrome of childhood.

Among a clinic sample of 6525 subjects, 61 males and 18 females with an ICD-9 diagnosis of the hyperkinetic syndrome of childhood were identified. Hyperactive girls had a lower IQ and significantly higher rates of language disorders and neurological disorders, suggesting a possible neurological basis for hyperactivity in females. In contrast, there was a population of male hyperactives with less evidence of brain dysfunction and a normal IQ, evidence compatible with the model of greater male constitutional variability. There was little evidence for the polygenetic multiple threshold model of sex inheritance.