Sir, – Adrienne Murphy ("Autism – it's not all about genetics", Health and Family, March 18th, 2014) argues that autism is not primarily a genetic disease, based on her experiences with her own son. While I sympathise with the desire of parents to find causes to explain their children's illness, they should be cautious of claims that the condition is caused by fluoride in the water, aluminium toxicity, GMOs, vaccines or any other supposed environmental toxins. There is no good evidence to support these claims, which amount to little more than conspiracy theories.
By contrast, the evidence that autism is primarily due to genetic insults is overwhelming. If one of a pair of identical twins is autistic, the chance that the other one will be too is over 80 per cent, while the rate in fraternal twins is less than 20 per cent. Any environmental exposures should not differ across identical versus fraternal twins – what does differ is the degree of genetic similarity. More generally, if you are related to someone with autism, your risk of autism is vastly increased over the population average (unlike adoptive siblings who are at no increased risk, despite sharing the same environment). We now know that the condition can be caused by mutation of any one of several hundred different genes, many involved in how the brain develops. Around a third of cases can currently be diagnosed with a specific genetic condition and that number is increasing rapidly.
In a subset of cases, these conditions are associated with additional problems, including gastrointestinal symptoms. These can sometimes be ameliorated by dietary interventions, which may well affect behaviour and improve quality of life for those patients. That does not mean that nutritionists can cure autism, any more than homeopaths can. – Yours, etc,
KEVIN MITCHELL, PhD
Associate Professor
of Genetics
and Neuroscience,
Trinity College Dublin,
Dublin 2.