Autoimmune Thyroid Disease

An Unfortunate and Lengthy Adventure in Misdiagnosis

Two genetic theories of autism

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If you’ve had a chance to read and digest The Times article I posted yesterday, I’d like to elaborate.

I posted this article because it is a pretty good overview of where modern mainstream medicine is at the moment. Genes aren’t specifically named in the article, but the subtext of ‘many common polymorphisms’ seems to be there.

Autism is thought to be caused by polymorphisms and mutations in various different neurotransmitter receptor/signalling/transport genes – such as the dopamine receptor genes I mentioned. In addition scientists have been looking at alterations in glutamate signalling/function as well as serotonin signalling/function.

The article lays out the two main genetic theories of autism:

  1. Autism is caused by a ‘cocktail’ of different single nucleotide polymorphisms that have different effects on the personality, and when a particular combination appears together, this produces an extreme result as in autism.
  2. Autism is caused by ‘random new mutations’ that change the function of the brain, because many new mutations have been found in autistic children.

In my opinion, it is the first theory which produces the second effect.

In other words, the ‘cocktail’ of different genes are the naturally occurring, heritable polymorphisms. These polymorphisms are not new and have existed for millions of years. Similar polymorphisms occur in most other species and are not restricted to Homo Sapiens Sapiens.

There’s little substance and much belief among some members of WAPF at the moment that autism must be caused by DNA undermethylation – that autistics are Pottenger’s children because of the bad diet of their parents, and what you need to avoid autism is lots of folate during pregancy. In fact what is suggested by the science is that only a ten percent minority of autistics have ‘random new mutations’, and these may or may not be influenced by folate consumption.

It is unclear how much epigenetics has to do with autism. Just as poor DNA methylation and other  non-nutritional factors produce spontaneous mutations, methylation also has the effect of reprogramming or turning on and off existing ‘transposon’ genes – the small percentage of junk genetic code added to our DNA by viruses. There is no evidence that autism is an epigenetic condition or not an epigenetic condition, but there is plenty of existing evidence that it is a regular genetic cocktail effect based on normal genes. We seem to have a perfectly plausible and fully working understanding of autism spectrum without adding epigenetics into the mix. However, certain named and well understood forms of autism like Rett syndrome (missing X chromosome) and Fragile X have been connected to possible undermethylation of DNA in already risky genotypes.

People with polymorphisms in their methylation genes (like MTHFR variants) are known to have higher rates of neural tube defects and spontaneous genetic mutations than the rest of the population – a problem that is not always fixable with folate, particularly when an inefficient enzyme is already working to capacity. MTHFR polymorphisms in and of themselves reach high statistical significance within autistic populations, along with COMT and GST. MAO-A has been linked to autism severity, with sex-linked differences connected to the fact that MAO-A resides on the female X chromosome so boys only have one copy. Only MTHFR is directly related to DNA methylation. Further, there is a survival advantage in MTHFR variants, it’s a classic example of ‘the selfish gene’ at work – the more and faster you mutate, the quicker you can adapt to new environments, and the faster you will outpace other members of your species. The disproportionate number of new mutations found in the genes of autistic children could well be as a result of a crunched up methylation cycle in the parents that is perfectly natural. I prefer this theory to the over-simplistic parental-blame-apportioning theory from holier-than-thou WAPF members.


Written by alienrobotgirl

28 August, 2007 at 1:56 pm

Posted in Autism Genetics

2 Responses

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  1. […] What are the odds of new mutations causing autism? Posted in Autism Genetics by the witch on February 7th, 2008 This is to follow on from previous posts I’ve made about the Autism Genome Project and the two genetic theories of autism. […]

  2. […] Posted in Autism Genetics by the witch on April 26th, 2008 Following on from the two genetic theories of autism I’ve discussed before, and the questioning of the odds involved in new mutations causing […]

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