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Friday, December 19, 2014

Are Autism Rates Really Rising?

Posted by jlwile on August 26, 2010

In a previous post, I discussed the rise in autism that seems to be occurring in the United States. In that discussion, I made it clear that genetically-based diseases can increase over time. One commenter (Eric) suggested that autism is not rising all that rapidly in the United States. This prompted a spirited exchange, which I enjoyed, and I hope Eric enjoyed as well.

The comments on that article are now closed, but Eric recently commented on another post to add a link related to that previous discussion. It is an excellent link, so I want to share it in a post that clearly relates to autism.

In essence, the author (an academic clinical neurologist at Yale) is skeptical that there is any significant increase in autism itself. Instead, he thinks that broadened diagnostic criteria for autism as well as increased surveillance have caused the number of diagnosed cases of autism to increase, but the actual number of autism cases has not increased much over the years. We are just doing a better job of diagnosing it, watching for it, etc.

You should read the article and see what you think. I personally think the Bearman studies he mentions (it was a series of studies, not just a single study – see this New Scientist article) are the most convincing, and they argue that there is a real increase in the rate of autism. Even the author of the original link seems to be willing to admit that increasing parental age (which I highlighted in my previous post) is causing at least some real increase in the prevalence of autism.

Comments

8 Responses to “Are Autism Rates Really Rising?”
  1. For what it’s worth, even genetically-linked illnesses can have a non-genetic basis. For instance, the genetic Cytochrome C Oxidase Deficiency can be reproduced in mice *without* the genetic defect by subjecting them to a Copper-deficient diet.

  2. jlwile says:

    Jonathan, you are certainly correct. Many times, genes and environment interact, but many times, they do not. In Cytochrome C Oxidase Deficiency, for example, the genetic trait is that one or more of the proteins involved in the insertion of copper into the mitochondrial cytochrome c oxidase are mutated. As a result, copper transport does not occur as efficiently as it should. Thus, you can mitigate the effects of the disease by increasing the amount of copper in the cells, and you can worsen them by lowering the amount of copper. Even if you don’t have the genetic disorder, you can mimic the effect of the disease by reducing copper in the cells. With little copper there, even efficient transport is not good enough, so you get the same symptoms. However, at that point it is not a genetic disease at all. It is a nutritional deficiency that gives the same symptoms as the disease. Nevertheless, that disease is definitely an example of how genetics and environment work together.

    However, in genetic diseases like Huntington’s disease, it’s pretty much all about the genes. If you have the mutation, you have the disease. If you don’t have the mutation, you don’t have the disease.

    Based on the twin studies discussed in the previous post, while there does seem to be some environmental effect, autism looks to be heavily genetic.

  3. Eric says:

    Wow, thanks Dr. Wile for posting about my link! I did enjoy it. While I agree with your writing here, the problem I had with the previous post was this:

    “Is is really possible that human genetics is changing so rapidly that a genetic disease has increased 18-fold in less than 20 years? Surprisingly, the answer to that question is “Yes.””

    Bearman says parental age can account for 11% of the increase in the last 20 years. The other two factors that add up to half of the increase explained are not genetic. Novella speculates that the rest of the increase is also not genetic.

    So the basic problem I have is with “human genetics is changing so rapidly”. I don’t think you can describe increasing parental age with this phrase. The degrading of sperm over the course of a life is very different from the common understanding of genetic change – mutated genes anywhere in the entire genome being passed down correctly to offspring.

  4. jlwile says:

    Hi Eric. No need to thank me for posting about your link. It was an excellent link and deserved to be highlighted. I still have to disagree with you on your assessment of my previous article, however. First, I did not say that human genetics HAS caused an 18-fold increase in less than 20 years. I said it was POSSIBLE for it to, and that is clearly the case. If you read J.C. Sanford’s book Genetic Entropy and the Mystery of the Genome, you will learn how rapidly human genetics is changing. Indeed, he highlights one peer-reviewed paper in genetics with the title, “Why aren’t we dead 100 times over?” The point of the article is that mutations seem to be accumulating in the human genome so rapidly that it doesn’t seem like the human race should be able to survive for a long time.

    I do think that increasing parental age is a way that human genetics is changing rapidly. Once again, older sperm and (to a lesser extent) older eggs accumulate mutations, and that causes rapid change in the human genome. Bearman says it can account for only 11% of the apparent rise in autism. I could quibble with that number a bit, but even 11% of an 18-fold increase in less than 20 years is still a rapid increase, which means rapid genetic change.

  5. Eric says:

    Well, I prefer to stay in the realm of the has rather than the possible. Lots of things are possible, but haven’t happened.

    In your last conclusion, do you mean there is rapid genetic change in the offspring of the oldest aged fathers, or of the population as a whole?

  6. jlwile says:

    But as a scientist, I must consider what is POSSIBLE. Determining the POSSIBLE causes of the rise in autism rates is the first step to designing studies that determine what is ACTUALLY causing the rise.

    The rapid genetic change is for the population as a whole. Even if the Bearman study is right and “only” 11% of the rise in autism rate is due to the rise in parental age, that still means the rise in parental age has caused a nearly 2-fold increase in less than 20 years. That is a rapid increase, and it indicates that the population’s genetics have changed rapidly.

  7. The Black Sheep says:

    Having not thoroughly investigated the studies you have linked to, I find this topic fascinating and would love to see more discussion about it.

  8. jlwile says:

    Black Sheep, I will try to oblige!

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