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 Purkinje cells produced from the cerebellar ventricular zone, and the glutamatergic granule neurons produced from the rhombic lip, and the preservation of the cytoarchitecture in the adjacent cerebellar folia suggest that the final steps of migration and networking are disturbed mainly or exclusively in the nodule of the majority of autistic subjects. The characteristic feature distinguishing lobule X from the other lobules is the abundance of the transcription factor Tbr2 positive unipolar brush cells (UBCs) [30, 34], which amplify inputs from vestibular ganglia and nuclei, by spreading and prolonging excitation within the internal granular layer [84]. Abnormal networking of Purkinje cells, granule neurons, and UBCs may contribute to altered cerebellar coordination of locomotion and motor learning and planning, as well as of higher cognitive processing [58]. Flocculonodular dysplasia appears to be another sign of the mosaic of local developmental defects, most likely predetermined by the spatial patterning of germinal zones in developing rhombic lip [110], and coexisting with more general
