We report a spectrum of focal developmental changes seen in the cerebellum of eight autistic subjects, including nodular (lobe X) [97] dysplasia in the cerebellum in five, vermal dysplasia in one, severe focal hypoplasia in one, and heterotopias in one other subject. The presence of heterotopias only in one control subject is evidence of a strong tendency for focal developmental changes of cerebellar microarchitecture that were present in 61% of the autistic subjects. Flocculonodular dysplasia affecting almost the entire lobe indicates that mechanisms leading to focal dysplasia, which were present in five (38%) of the autistic subjects, show extremely strong topographic predilection. The observed focal dysplasia was associated with profound local disorganization of granule cells, Purkinje cells and molecular layers limited to a small cerebellar compartment receiving major projections from the vestibular complex involved in the oculomotor and postural system. Similar cerebellar dysplastic changes classified as heterotaxias (clusters of poorly organized mixed cells) were identified in 14% of normal infants but in 83% of infants with trisomy of different chromosomes [92]. The presence within the dysplastic nodule of both GABAergic
