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The Role of Genetics and Environmental Factors in Causing Autism

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Autism: The Way I See It

The Role of Genetics and Environmental Factors In Causing Autism

by Temple Grandin

Autism Asperger’s Digest | July/August 2009

 

At the 2008 Geneva Center Autism Conference inToronto, Dr. Peter Szatmari, Professor of Child Psychiatry atMcMastersUniversity, presented a clear, easy to understand explanation of how genetics is involved in the cause of autism. According to Szatmari, there are three main genetic mechanisms that cause autistic symptoms.

About 7% of all autism cases are caused by major chromosome abnormalities where the chromosomes are either broken or scrambled. These abnormalities are so severe that they are visible under a light microscope.

Another 3% of autism cases are caused by major, readily diagnosable, genetic syndromes such as Fragile X. The other 90% of autism cases are slowly being tracked down to copy number variations in genetic code (CNVs). CNVs cannot be seen under a microscope; they can only be seen with gene sequencing equipment that can make copies of the genetic code. Genetic code is similar to a computer code. Instead of being binary with two digits it consists of millions of bits of four digit code along the chromosome.

CNVs are either inherited or may be caused by de novo mutation (not inherited from either parent). Small mistakes in copying the code can occur, such as reversing letters, adding extra sections of code, or microdeletions of parts of a section of code. This can happen spontaneously, sort of like the errors that are made when printed documents are scanned into a computer. Sebat et al. (2007) in The Journal of Science reported that random copying mistakes account for autism in families where there is only one autistic child and no autism in the parents. This accounts for another 10% of all autism cases.

In the next conference presentation, Dr. Martha Herbert, Assistant Professor of Neurology at Harvard, speculated that the so-called random copying errors may be caused by environmental contaminants that damage genetic code. She showed two slides of the state ofTexas. One slide showed the location of oil refineries and chemical plants and the other showed autism cases inTexas. When one looks at the two maps, it becomes obvious that there are more autism cases near the chemical plants.

A New View Toward Diagnosis

Dr. Szatmari explained that 15-20% of all autism cases can now be explained by the previously described mechanisms. Tracking down the cause of the other 80% will require gene sequencing 5,000 children and breaking autism down into some of its component parts instead of just diagnosing children as autistic. Three components that have already been studied are: 1) cognitive impairment, 2) language delay, and 3) abnormal nonverbal gestures. When children are classified in this manner, separate CNV problems on specific chromosomes have been found. Szatmari speculates that autism is probably composed of deficits in different brain systems that can be linked to sequences of code that control brain development. It is likely that many more components will be determined, essentially changing our view of autism as not a single disorder, but one having many subgroups of impairment. Understanding of the disorder will be better when each component is looked at separately.

Autism/Asperger and Normal Personality Variation?

I was asked to respond to Dr. Szatmari’s talk. I have learned from reading lots of scientific papers that CNVs are inherited in a very complex manner and they cannot be explained by the simple Medalian genetics you learned in high school. Major components of human personality and variation are probably explained by variations in CNVs. I think mild Asperger’s is simply a personality variant.

If all the pieces of code that created autism were removed, I predict the children would be yak yak social air heads and probably pretty unintelligent. When I wrote Thinking in Pictures in 1995, I wrote that a little bit of an autistic trait could provide an advantage and too much of the trait, a severe handicap. Preventing severe autism would be a worthy goal, but preventing mild autism and Asperger’s would be a grave mistake. The world would lose many creative people who have made the world a much more interesting place.

References

Liu, X.O., Peterson, A.D., and P. Szatmari. 2008. “Genome wide linkage analysis of quantitative and categorical autism subtypes.” Biological Psychiatry, 64:561–570.

Sebat, J., et al. 2007. “Strong association of de novo copy number mutations with autism.” Science 316:445–449.

BIO

Temple Grandin is an internationally respected specialist in designing livestock handling systems. She is the most noted high-functioning person with autism in the world today.

Copyright © Autism Asperger’s Digest. 2009. All Rights Reserved.

Distribution via print means prohibited without written permission of publisher.

 


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