THE BRAIN IN INFANTILE-AUTISM - POSTERIOR-FOSSA STRUCTURES ARE ABNORMAL

Infantile autism is a neurologic disorder of social, cognitive, and la nguage development. Earlier MRI studies found hypoplasia of posterior vermal lobules VI and VII and cerebellar hemispheres in the majority o f autistic patients, and recent autopsy analyses find severe Purkinje neuron loss in the posterior vermis (lobules VI and VII and VIII to X) and hemispheres. A second type of cerebellar pathology in infantile a utism was recently found: hyperplasia (excessive enlargement) of poste rior vermal lobules VI and VII. If the autistic samples in some MRI st udies that did not detect cerebellar hypoplasia were actually composed of both the hypoplasia and hyperplasia subtypes, then the autistic me an size reported in such studies would have appeared to be near the no rmal mean size only because it would be the sum of the two opposite su btypes. To test this possibility, we statistically reanalyzed previous ly published vermal area measures of 78 autistic patients from four se parate studies. The results revealed that the autistic patient samples from these four studies were indeed composed of both the hypoplasia s ubtype (87%, 92%, 89%, and 84% of patients) and the hyperplasia subtyp e (13%, 8%, 11%, and 16% of patients). Cerebellar abnormalities have b een found in 15 autopsy and quantitative MRI reports from nine laborat ories involving a total of 226 autistic cases. Autism may be one of th e first developmental neuropsychiatric disorders for which substantial concordance exists among several independent microscopic and macrosco pic studies as to the location and type of neuroanatomic maldevelopmen t. Onset might be as early as the second trimester. Discovery of the e tiologies underlying cerebellar maldevelopment may be the key to uncov ering some of the causes of infantile autism.