No-one knows exactly what causes autism, although a lot of people have made very good educated guesses. The most common three ideas are:
It is quite possible – even likely – that genetics are a part of all sorts of autism. Although there have been cases of ‘spontaneous’ genetic autism rather than inherited, it is in most cases inherited.
Parents from families with autistic members are more likely to have children with an Autism Spectrum Disorder. Families which already have one children with an ASD are also more likely to have another.
Many parents claim that childhood immunisations are to blame for autism. There have been several theories, both convincing and unconvincing, but they have all been refuted by the medical communities.
This doesn’t stop countless mothers from joining the hordes of “ASD vaccine conspiracy theorists” each year.
Statistics seem to show that there is a higher rate of autism in developed countries than in undeveloped ones; however, this could just be because there tends to be less medical expertise and autism awareness in developing countries.
However, children and adults with an ASD often have multiple allergies, particularly to processed foods and food additives, as well as asthma, and also often seem to be more sensitive to the environment than neurotypical people. A change in diet often helps ameliorate the more severe ASD symptoms somewhat.
The general consensus is that autism is caused by a combination of a genetic predisposition towards Autism Spectrum Disorder, as well as outside factors such as environment and diet.