What Causes Autism Spectrum Disorders?
What Is Known about the Causes of ASDs?
There is much discussion on this issue, and research studies are often published that are sometimes disputed or explained away by other research. However, there is strong evidence for a genetic component and a biological basis. Most researchers believe that ASDs have different causes that may be affecting the same brain systems or hindering development by disrupting the different abilities needed for communicative and social development. Here is what is known and accepted to be true by almost everyone:
- There is a genetic predisposition to autism. Regions of interest, sometimes called "hot spots," have been found on certain chromosomes, the most important so far on chromosome 7q, although others are involved. If one identical twin has autism there is a 60-95 percent chance of the other having it as well. However, identical twins with the same genetic makeup and the same physical environment may have different expressions of ASDs—one may be very able, the other very disabled.
- There have been a number of findings in regard to differences in brain activity, not all in agreement with each other. However, most scientists who study autism would agree that some brain circuits are different in a person with an ASD.
- Serotonin, a neurotransmitter important for normal brain functioning and behavior, has been found elevated in a subgroup of people with autism and in some first-degree relatives who are unaffected. This is the only key biochemical finding since the 1960s that has held up to be true over time.
- There is a large body of anecdotal findings reported by parents and medical professionals that some children with ASDs appear to have biochemical and immunological problems. Some possible causes being mentioned are: mercury toxicity, yeast problems, casein and gluten sensitivity, and viral infections.
- In some studies, different levels of environmental toxins such as lead, antimony (a flame-retardant chemical present in many house-hold items), and aluminum have been found in hair and blood samples of children with autism than in those of nonautistic children. This leads to the hypothesis that some children with ASDs cannot detoxicate, and thus accumulate toxins in their bodies.
For a long time, the favored theory was that autism was all about the genes. It is true that genes come into play. However, the dramatic rise in recent years in ASDs cannot be attributed to a rise in genetic anomalies.
Perhaps we are seeing different disorders, each caused by a different problem but with symptoms resembling one another. Perhaps the differences are all being caused by a yet unknown single underlying cause.
It appears most likely that there is a genetic predisposition to autism spectrum disorders interacting with environmental factors that may play a key role in affecting the gastrointestinal tract, the immune system, the sensory nervous system, and the brain.
More on: Autism
Excerpted from Autism Spectrum Disorders: The Complete Guide to Understanding Autism, Asperger's Syndrome, Pervasive Developmental Disorder, and Other ASDs©2004 by Chantal Sicile-Kira. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.
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