Is there a relevant study showing that the autism is low among Amish? Some articles, e.g. this one have claimed it based on anecdotal evidence:
"I have not seen autism with the Amish," said Dr. Frank Noonan, a family practitioner in Lancaster County, Pa., who has treated thousands of Amish for a quarter-century.
"You'll find all the other stuff, but we don't find the autism. We're right in the heart of Amish country and seeing none, and that's just the way it is."