Despite what all the "experts" have told us, I believe the largest factor in autism is genetic. My husband is likely to be at least aspie, and he recognizes this in himself, or actually, did recognize it while we were going through testing for our youngest son. He has an aunt in Georgia with full-blown autism who must be cared for by her sister, she is only barely functional, and another uncle who is moderately functional
(interestingly enough, was also born with cleft palate, not sure if that's any connection or not). My oldest daughter and older son both have markers of asperger's, my youngest son has moderately high functioning autism. Birth distance makes no sense when the firstborn and the child born six years later are ones with markers, and the child born two years after that has autism. I think it's just as possible that the 'close birth spacing' may be a coincidence, since MANY families with autism have multiple children.