Scientific American has an article about autism every once in awhile.
I know that now it is considered a "spectrum disorder", meaning that it encompasses a wide range of severity. Current thinking is that there are multiple complex causes including both genetic and environmental factors. Some cases seem to involve digestive anomalies.
There is a lot of evidence to suggest that the increase in cases is not due only to better recognition, which raises the question of what environmental factors may be changing.
Sorry I'm not able to answer your questions. I just find this topic interesting every time it comes up.