I am high functioning autistic and wasn't diagnosed until I was 52 (I'm 65). Since my diagnosis, I've read tons about autism, watched videos, gone to autism conferences, and talked with autistic people and parents. The general consensus is that the predisposition for autism is genetic (inherited); however, some outside force "triggers" the child's brain to develop differently (autistic) between the age of 18 and 36 months. Without the trigger, the person's brain development would be normal. 1/2