This is an interesting little discovery:

A specific structural variation on chromosome 16 dramatically boosts the risk of autism, according to a study published today in the New England Journal of Medicine.

That would seem to be supporting Simon Baron Cohen’s ideas that autism is indeed genetic and that the rise in incidence is being driven by assortative mating. However, that might not be quite the way to read it.

The findings build on previous reports that autism is linked to genetic deletions or duplications that arise spontaneously, rather than being passed down through generations. In almost all cases, parents of the affected people did not carry the chromosome 16 variation.

Ah, there, you see? What they think they’ve found is that it is a spontaneous (another way of thinking about it is first generation) mutation. So it isn’t in fact something that is handed down from parents to children, it’s something which happens at the very earliest stages of the development of the fetus (or blastocyst perhaps). So this would seem to indicate that we’ve got something which refutes the Baron Cohen thesis. For, as we know, that entails that the condition of autism be inheritable.

So, should we simply throw out the whole idea (either of them, as they seem to be mutually incompatible)? No, not quite, for there’s a third part to their findings.

They found that deletion or duplication of approximately 500 of the same DNA letters on chromosome 16 was strongly linked to autism, accounting for about one percent of cases. “While that doesn’t sound like a huge number, the fact that these people carry the identical spontaneous deletion or duplication would be incredibly unlikely to happen by chance,”

We’re able to explain some one percent of autism cases this way. The other 99% are so far open to other explanations. And this leads us back to another contention of Baron Cohen’s, one that is generally not all that well known.

That there really isn’t a “disease” called autism. A disease implies one causative factor: what we really should be saying about autism is that it’s a condition. And the thing about conditions is that they can have multiple causes. Similarly, diseases can cause multiple conditions, not all of which show in each and every case (measles normally just produces a rash and a temperature but it can also cause brain damage). Congestive heart failure, for example, is a condition: it can have many causes (ie, many diseases or factors can cause it), pleurisy, cholestorol, viral infections and so on. And so with autism. We can see the diagnostic criteria in someone, but we don’t actually know what has caused them. Here we have a possible explanation for 1% of cases. I wouldn’t be at all surprised to find that the same diagnostic signs can be caused by more than one thing. Just as with heart disease.

As they say, more research is required here.