An epidemiological study [22], indicated that environmental factors such as toxic exposure, teratogens, perinatal insults, and prenatal infections such as rubella and cyto megalovirus account for some cases. Autism has been linked to a wide variety of prenatal and postnatal insults but predominantly 6 in individual case reports. The published literature on specific prenatal infectious pathogens known to affect the brain and ASD, including herpes simplex, rubella, syphilis, and varicella-zoster, consists mainly of occasional case reports [22]. Intrauterine exposure to the teratogenic drugs thalidomide and valproate and other anticonvulsants have been implicated as the cause of autism in a few affected children [23]. Taking thalidomide during days 20-24 of gestation was clearly correlated with an increased risk for an autistic disorder. It has been suggested that the MMR (measlesmumps- rubella) vaccine causes autism [24,25]. The widespread use of this vaccine has reportedly coincided with an increase in the incidence of autism, and there are case reports of children in whom signs of developmental regression and gastrointestinal symptoms developed shortly after vaccination. The measles virus has been found in the terminal ileum in children with developmental disorders and gastrointestinal symptoms but not in developmentally normal children with gastrointestinal symptoms. The measles virus used in the MMR vaccine is a live attenuated virus that normally causes no symptoms or only very mild ones. However, wild-type measles can infect the central nervous system and even cause postinfectious encephalo myelitis, probably as a result of an immune-mediated response to myelin proteins. Studies designed to evaluate the suggested link between MMR vaccination and autism do not support an association, and fail to confirm that immunization with the MMR vaccine is responsible for the upsurge in autism [24,25].