I have two friends, each with a set of twins. One fraternal the other identical. My friend with the identical boys, both are severely autistic. My other friend, one boy is gifted and talented, the other severely autistic and died from seizure complications at 19 years old. One could argue that in both cases the fetuses were exposed to the same environment in utero. Fraternal twins:one is born with it, the other isn't. Different genes? The identical, both are born with it... exposed to same uterine experience and genes. It would be interesting to follow twin cases to see if connections can be found that could lead researchers down the right path.