Increased brain mass in autistic children and some autistic adults [89], increase in the numerical density of neurons [13, 14], reduced size of neurons [7] and brain structure-specific delay of neuronal growth [111] indicate alterations in neuronal and brain growth in autistic individuals. The subventricular zone of the lateral ventricles [26] and the dentate gyrus [33] are active sites of neurogenesis in adult humans. Several of our findings support the hypothesis of altered neurogenesis in autistic subjects. The increased thickness of the subependymal cell layer, subependymal nodular dysplasia, abnormal growth of the dentate nucleus and dysplasia of the granule layer in the dentate gyrus, detected in this study, appear to be signs of abnormal neurogenesis in the brains of three autistic subjects. Subependymal nodules were reported in approximately 80% of patients with tuberous sclerosis, a disorder that is highly associated with epilepsy, autism and mental retardation [73]. Tuberous sclerosis nodules were detected in one fetus [12], suggesting that fetal development of subependymal nodules can lead to the early onset of epilepsy that was diagnosed at the age of 14 months
