At present there is no conclusive cause or cure of autism. However there is considerable research which points to a genetic base, with biological or neurological differences in the brain. This seems to be the most enthusiastically pursued option for finding answers to the autism question.

Other causes under consideration, but unproven, include pre-natal or post-natal viral infection, or environmental assault to a compromised central nervous system. Research is also occurring in the study of brain structure abnormality.

Genetic Factors:
Although research has failed to find a specific gene marker for autism, findings of familial studies and the greater prevalence in males than females strongly suggest a possible genetic involvement. Among identical twins both are afflicted with autism in approximately 82-86% of cases. The rate among fraternal twins is 25%. The syndrome of autism has been found to be more common in the siblings of a child with the disorder than in the general population. That is, if parents have one child with autism, they have an increased chance of having another child with the same disorder (i.e., the rate of autism amongst siblings is approximately 2%). In 7 to 10 percent of the autistic population, a syndrome called Fragile X has been identified, involving a break or weakness in the formation of the X chromosome. The correlation between Fragile X syndrome and autism has not been proven.

Family/Genetic Information
Among identical twins both are afflicted in approximately 82 - 86% of cases. The rate among fraternal twins is 25% and 2/100 siblings of autistic children are also later diagnosed with autism.

Source: Canadian National Autism Foundation