[Perna]

How severe a child's autism is may depend on when s/he develops it.

http://www.healthday.com/Article.asp?AID=638397

[Callista]

Seems to me the difference isn't the age of "onset", but the presence or absence of regression.

From the autistic people I've talked to who tend to lose skills (rather than just losing access to skills), it seems to happen during times of high stress--whether that means developmental demands, environmental stress, or some combination of the two.

The first time period that places serious demands on a child is the toddler years. This is when you're expected to learn to walk and talk, to learn to self-regulate, to deny gratification to some extent, and to begin to integrate yourself into society. Typical children tend to have serious temper tantrums during this time just because they are so frustrated. Put an autistic child in that same situation, and the stress is a hundred times as bad.

My mom still talks about how bad my toddler years were. I've never lost skills; the worst that ever happens to me is that I don't have enough cognitive "fuel" to access them. I've never had to re-learn anything. During those years, though, it must've been obvious how much pressure I was under, because I didn't sleep through the night until I was six years old, spent hours running in circles, and had tantrums that also lasted hours. Similar transition years are the first grade (beginning of school), puberty (high school and physical maturity; demands for increased independence), and adulthood (demands for complete independence). At all these points in my life, things have gotten a great deal more difficult for me.

My kind of autism is not regressive, so I didn't lose skills when the stress meter topped out; I only lost access to them (at nineteen I was in the hospital for depression; at fourteen, I should have been). But a child who was more sensitive to stress, who will actually lose skills when exposed to these sudden expectations, could easily be brought to the point where he just couldn't keep juggling all those new things. Constantly bombarded with sensory data, expected to learn new things, with a great deal of pressure put on him--pressure that's completely normal for a typical toddler--such a child will tend to preserve what cognitive resources he can, and drop the most precariously held skills.

The solution seems to be to create a favorable environment, drop non-essential things, and teach slowly and carefully.

It's not like we're fragile people made of blown glass, going to break any second; it's actually something that could happen to anybody. People have breakdowns all the time; burnout is a household term that everybody's familiar with. It's just that there are more things that can cause it in an autistic person. The threshold is just much lower. Most of the trick of living with autism is knowing your limits.