Causes of autism

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Are there any definite causes of autism? Why have cases of autism increased?

Cases of autism have increased to better screening tools, and the fact that there is a larger number of spectrum disorders under the same umbrella, than there used to be, and more awareness, as well.

It's a bit too complex to have a simple, definitive answer. We know genetics are involved. Engineers are more likely to give rise to autistic progeny.


There is insufficient epidemiological evidence to conclude that cases of autism have increased. One study showed more or less constant rates of autism across age brackets, implying that the rate has remained fairly static as we have never observed adult-onset autism.

My other question is, why do symptoms of autism show up later...like when a child is 3 or 4 years old? I've even read that it usually starts out suddenly....out of nowhere

I think it all has to do with the DSM - diagnostical manual that psychiatrists use. Personally, I have a bone to pick with psychiatrists because they'll shove a person into one of the DSM pigeonholes whether they fit or not. Or they'll say there's nothing wrong with you, when there certainly is but it's not in the DSM.

Anyway, Asperger's was put into the DSM in 1994 - so I am seen as a "new" diagnosis, when in fact it was the doctors making a wrong diagnosis until then. But heaven forfend they should blame themselves.

As for the sudden appearance of symptoms at the age of three, autism is a developmental disorder. So the child has to do some developing up to the stage where "normal" behaviour should appear. Let me give an example. All babies, when they first learn to walk, flap their arms, move their legs up and down without forward motion, and laugh delightedly, That's normal. But the exact same behaviour at a higher age is possibly symptomatic of autism or something else.

The "starts suddenly" variant is childhood disintegrative disorder--an extremely rare form of autism that some people think probably does not have the same genetic cause as autism proper. The vast majority of cases have been present from birth, but because autism affects skills that you only start to expect of children in their toddler years (age two or three), it only becomes obvious, in many cases, when the child doesn't get those skills along with his peer group.

The toddler years are also extremely stressful and developmentally demanding; while a baby is only required to lie there and babble a bit, reach for things, and possibly look Mommy in the eye, a toddler is expected to learn an entire language, learn to share, learn to process his own emotions, learn to count and tell letters apart, etc. The language explosion of the toddler years is where autistics often start getting left behind. The child is diagnosed, and the parents look back and think, "Hmm... he was odd all along." It just didn't seem serious until language got left behind.

The other developmental stage where autism can become apparent is the kindergarten through first or second grade, where social demands increase sharply and autistics who learned speech with not too much trouble will start to show up as being far behind their peers in things like back-and-forth conversation, understanding friendships, etc.

Actually, autism becomes more obvious anytime some large parcel of new skills is required of a child... that includes things like the early teens, where people are expected to have all the self-care skills down, and the late teens, where people are expected to become independent adults.

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Sometimes awareness of a new area - autism - tends to increase the number of diagnoses it seems to me.