During the development of a child, most brain cells are generated before birth. There is one group of brain cells, however, that are generated in large numbers in infancy. This occurs in a brain region called the hippocampus. These cells are important for the normal development of memory, cognition and language, and disruption of these cells is present in children with autism. The proposed studies seek to better elucidate the causes of autism by determining whether selective disruption of late-generated neurons - specifically hippocampal dentate granule cells - contributes to key features of autism. This will be achieved using a novel combination of transgenic mice to selectively eliminate a gene, PTEN, implicated in autism, from these late-generated neurons. Significantly, although the proximal cause of autism remains to be determined in most cases, the late generation of these neurons (in the late embryonic period and in infancy) may make them uniquely vulnerable to a variety of insults faced by the newborn child (e.g. infection). The proposal will also examine the role of granule cells in the development of epilepsy, the condition most commonly associated with autism. Demonstrating that these cells play an important role in the development of autism (or associated conditions like epilepsy), will provide a compelling rationale to develop new therapies to protect these vulnerable cells.