This is a very difficult question to answer, because there are different causes for autism and Aspergers, with some of these conditions being highly heritable and others are not.

Most scientists agree that these conditions on the autism spectrum are caused by a combination of biological and possibly environmental factors, with the resulting genetic anomalies affecting brain growth and development. Possible environmental factors, such as parental age or exposure to toxins during pregnancy may contribute to some of the ‘autisms’. The genetic anomalies may or may not be inherited from the parents because some autism spectrum conditions are due to what is called ‘de novo mutations’. These are mutations that happen spontaneously, without a known cause, in the father’s sperm or mother’s egg, or early in the development of the embryo. To what extent the environmental factors contribute to these de novo mutations is not known.

When autism (or Aspergers) runs in families it is clear that they are at least partially inherited from the parents and/or the extended family. The parents or other family members may not necessarily have a diagnosis, but are carriers of genetic anomalies which in combination may cause autism in their offspring. And once there is one child with autism in the family the chances of this family having another child with autism increases from 1-2% (1 – 2 in 100 children in the general population have autism) to nearly 20% (1 in 5 children).

Exactly which genes and which combinations of genes are involved remain unknown, with between 300-400 genes implicated to date. Thus the consensus amongst scientists is that it is likely to be many genes and that variations may vary from individual to individual. This makes the calculation of risk in individual families extremely complex, if not impossible at this time.

If you are concerned about this issue of heritability, we advise you to consult a genetic counsellor who may help you identify some ways of decreasing risk, such as ‘sorting’ female and male embryos (as the risk of autism and Aspergers is lower for females). We do not necessarily recommend this intervention, and such approaches may be costly.

– Dr Elfriede Ihsen