The case of little Great Agbonlahor is in the news again today. For those of you that don’t know, this six year old boy, whose name is “Great” (yes, not such a common name in Ireland) is autistic. He has lived with his mother Olivia and his twin sister Melissa in Kerry for the past five years. Now they face deportation to Nigeria, where they are from originally. It is making news because there is concern that Great will not get the kind of medical care that he might get in Ireland.

Much has been written about the causes of Autism. The allegation that there is a link with child vaccination programs is a dangerous and incorrect allegation that has been in circulation for some time. Let me state what I know about Autism Spectrum Disorder (overall frequency is ~1 in 150 births).

First of all, there is no significant difference between the frequency or age of onset of autism in populations that have been given the 3-in-1 vaccine and those that have not been given the vaccine. Vaccination is VERY VERY important for any population and this kind of irrational scaremongering is responsible for the deaths of unvaccinated Irish children every year because their parents are too scared to vaccinate.

Secondly, what most people probably don’t realise is that there is a significant genetic component to Autism. We know this because we now have enough incidences of autism in twins to be able to do some calculations.

If we take identical twins first of all. In this case, if one twin develops autism, then the likelihood is about 70% that the other twin will also develop autism.

If we take non-identical twins, the likelihood of twin B developing autism if twin A has autism is much lower (0-10%).

These numbers vary from study to study, but monozygotic (identical) twins generally have a several-fold higher incidence of concordance.

Unlike cystic fibrosis (CF), the inheritance pattern of autism is not straightforward. This is because, unlike CF, there is more than one gene involved and depending on your collection of genes, you might or might not develop autism. Indeed, there is a spectrum of diagnostic criteria for autism.

Therefore, we say that autism is more similar to familial cancers or diabetes in the sense that autism ‘tends to run in families’. This is not the whole story either.

We see sporadic autism in families where there is no history. This is presumably because of de novo mutation. We all have new mutations - this is inherent in the genetic machinery - so in some autism cases, autism is caused by new mutations.

Autism occurs more in boys. This is probably because there is something about a girls genetics that causes her to overcome or mask the effects of the autism-associated genes.

So, what causes autism? In large part it is genetics. In some part it is the environment. According to an extremely large study in Denmark, in no part is it the 3-in-1 vaccine.

Comments welcome.