Saturday, December 31, 2011

Genetics and Autism

I've been sitting on this report for a month or two while I did a bit more research on the original sources and similar studies. As regular readers of this blog know, I believe autism is better described as "autisms" and that likely contributors include de novo genetic complications (sometimes called pre-natal genetic copy variation). In these forms of autism, genes replication introduces errors. This is not the genetic of heredity, a common misconception when the term "genetic" is used to describe some forms of autism.

From CBS News:
Children with autism have distinct facial features
For the study - published in the Oct. 14 issue of Molecular Autism - researchers compared facial features in 64 boys with autism with faces of 41 typically developing boys, all 8-12 years old, with a 3-D camera system. After mapping out 17 points on faces, the researchers found significant differences between the two groups. 
The study found children with autism had wider eyes, and a "broader upper face," compared with typically developing children. According to the study, children with autism also had a shorter middle region of the face - including the nose and cheeks - as well as a wider mouth and philtrum, the divot above the lip and below the nose.
Our default physical features are genetic. (Injuries, diet, and other factors can change those features, but the default is what I am addressing.) There are several genetic neurological conditions that are accompanied by physical characteristics. Some of these conditions are inherited, while other are de novo replication errors. What's important is that this study suggests at least some forms of autism can be "seen" via facial characteristics.

The evidence of a correlation between facial traits and autism was found by the researchers. The more horizontally oval a young boy's face, the more pronounced the autistic characteristics. Because more than 50 boys with autism were examined, the statistical likelihood that this can be generalized is significant.
The study also found that children with more severe autism traits such as behavioral problems, language difficulties, and repetitive behaviors had distinct facial differences from other children with milder autism.
Previous research has found that autism is associated with an increased neural density in the frontal cortex and left frontal lobe regions of the brain. This neural density is the result of de novo "over replication" of some cells. Basically, the forming brain won't stop forming when it reaches the normal stopping point. More and more neurons are created, especially in the part of the brain that controls executive functions.

In 2011, Dr. Eric Courchesne presented a paper on this at the International Meeting for Autism Research. Dr. Courchesne found that autistic individuals have 25% to 65% more neurons in regions of the frontal cortex than are present in typically-developing individuals. (see: http://jama.ama-assn.org/content/306/18/2001)

The increase in neurons originates during cell division occurring between the 13th and 18th week of pregnancy. The early second trimester is when neurons develop. There is no known mechanism that could produce this abundance of neurons after birth, either.

The University of California MIND Institute found that this abundance of neurons is prevalent among autistic children who experienced "regression" — seemingly going from normal development backwards to a non-verbal stage. I've read various theories on this, from "the brain is too big" to "the brain gets overwhelmed."

We don't test "normal" children with MRIs to measure neural density. The only way we will know if the density does predict regressive forms of autism is to scan several thousand children shortly after birth and every six months from then on, until we start to determine which children are autistic.

I want to remind readers, again, that anything we learn about "autism" likely applies only to some people we describe as "autistic." For now, "autism" is a catchall that is more likely to be several different conditions. We are learning more every year, and what we learn also reveals how much we don't know.

Additional Sources:

Courchesne, E. et al. Neuron Number and Size in Prefrontal Cortex of Children With Autism. JAMA.2011; 306(18):2001-2010. doi:10.1001/jama.2011.1638

Lainhart, J. and N. Lange. Increased Neuron Number and Head Size in Autism. JAMA. 2011; 306(18):2031-2032. doi:10.1001/jama.2011.1633

2 comments:

  1. Oh good. More fodder for the "but he doesn't look autistic" people. :)

    Anyway, very interesting article. Thanks.

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  2. I hope that people realize any genetic "cause" is likely to be associated with only some "autisms" -- not the complete spectrum of disorders we place within the umbrella. Still, I do understand the problem; some people talk about the disabled "looking angelic" and I've never been comfortable with that notion.

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