Thursday, February 5, 2009

Study Watch : Nuclear and Mitochondrial Genome Defects in Autisms

An interesting study came out recently entitled Nuclear and Mitochondrial Genome Defects in Autisms. It is an open access study so you can go and read it for yourself.

This study is basically a review of some of the known genetic defects that are implicated in autism. It is a little on the dense side but if you are interested in the topic (or are having trouble sleeping) it is good reading.

The part that I found most interesting was the section on monozygotic (identical) twins - since my children with autism are identical twins I guess this is only natural. The authors discuss some of the research that others have done and discuss their own results with two sets of twins.

I am sure that I will get some of the terminology wrong and am missing some of the nuances that are in the original text, but...

Basically one of the two sets of identical twins differed in the degree of severity of autism and when they looked at the genetics of the twins they found very small differences. The twin that exhibited more genetic variance was the more severe of the two.

The authors also note other studies that also show some differences in twin pairs.

The questions I have, and maybe I am missing obvious, but given the fact that identical twins are basically identical - especially at very young ages when autism is thought to develop - what causes the genetic differences between the twins? And how is it possible for the twins to have different levels of severity if autism is genetically determined?

Anyone know?


  1. The answer is that autism is not genetically determined. Genetic factors create susceptibility to injury but are not determinative.

    There are also epigenetic influences but these are determined by non-genetic factors including environmental factors such as diet and toxic exposures.

    No study has found 100% concordance of autism in twins. Even clearly genetic factors such as found in Fragile X syndrome is not strictly determinative. Not all individuals with Fragile X are autistic or impaired.

    Every finding of an "autism gene" involves a pathway in which the gene plays a role, but the pathway is influenced by other factors, such as toxins.

    Combination of genetic variation likely plays a role in the cause of autism but not an exclusive role.

    There exists no study of the genome that has identified an exclusive genetic cause of autism despite the expenditure of millions of dollars and extravagant claims by geneticists.

    Genetic research is valuable because it can point to the key metabolic pathways that play a role in autism. There are many examples of this in the literature.

  2. Bob - Thanks for the answer.

    I understand some of the epigenetic influences, but what I do not understand is how the changes can happen. The environment in general can do it, but by what process exactly do these changes occur? This is most likely just my ignorance of the field talking, I am sure this has a known answer.

    Also, what I understand these changes can build up over a lifetime to the point where even identical twins are very different. Yet at a very young age there should not enough differences there to cause a difference as significant as autism. And if there is a significant difference at a young age shouldn't there be some way of finding these differences and by relation get a clear picture of what caused them?

    For what it is worth I agree with what you are saying, I just wish I understood the exact process that is going on better and I wish there was better research in the area.