As a nutritionist, I have read quite a bit over the years, and worked with a few parents of such children.
In my opinion: Congenital autism is real and rare. Induced autistic symptoms may arise either pre- or post-natally, due to a toxic load too heavy for a small body with an immature immune system.
AMA types may scoff, but the human body was not designed to scavange unlimited quantities of unnatural (artificial, not merely synthetic) chemicals.
The induced type often improves somewhat by regulating methylation.
Correction: congenital autism should be genetic autism.
Obviously, a pre-natally induced condition is congenital. Also, while I think there can be a genetic component to the induced type, I also think that is distinct from the classic autism.
Amazing literacy!