My personal guess is that these are quite distinct – both in terms of symptoms and in terms of etiology.

My son did not “regress” in the accepted sense – nor did he develop health issues so often connected with autism (gut, sleep, seizure). My sense is that those health issues are far more common with dramatic regression – though could be wrong!

Lisa (autism.about.com)

I have interviews conducted with my mother and father reflecting on my early months. I was not responsive in the “normal” sense, which is why they assumed there was severe brain damage. I was “disconnected” from my social environment, and hypersensitive to my physical existence.

Well before I was even three or four months old, it was known there was a problem. My parents simply didn’t give up… and that was in the late 1960s.

Was it my birth? Were there underlying genetic issues? I don’t know. I do know I wasn’t given vaccines until long after I was diagnosed as likely MR. I was simply an “FLK” (Grinker 2007).

For us M does move forward and regress continually. Her Autism is a tad different in that way. No doubt due to her very rare chromosome disorder and CVS.

“One reason that I have not necessarily considered an external trigger as necessary to be responsible is that I recalled from developmental biology that at some point in infancy/early childhood, brain function and processing changes.”

Charlie too just did not develop certain skills, language most obviously. Also: He would sometimes show the first glimmer of speech or imitation and then get to a point and not progress farther with it (a pattern we still see in his learning today).