Pneumoencephalographic and clinical findings of the XYY syndrome.

In order to approach the hitherto unknown brain involvement in the XYY syndrome five adult patients with this syndrome were studied clinically and pneumoencephalographically. Clinical manifestations included delayed difficulties of speech and learning, clumsiness, mild intention tremor, muscular hypotonia, convulsions, hyperactivity, distractibility, impulsiveness, weak mental control, psychosexual disturbances and a slight defect of intelligence. All five had committed crimes. Pneumoencephalograms showed general ventricular enlargement of mild or moderate degree. The enlargement of lateral ventricles was unilateral or asymmetrically bilateral. The suprapineal recess of the third ventricle was uniformly enlarged. Small cerebellum and enlarged fourth ventricle were the abnormal findings in the posterior fossa. No cortical abnormalities were found. The clinical and pneumoencephalographic findings suggest a slight non-progressive developmental disorder of the brain resembling the so-called minimal brain dysfunction syndrome. The XYY syndrome appears to be one cause of the male preponderance in minimal brain dysfunction syndrome and criminal psychopathy.