There is no single cause of autism, in the same way as there is also no single type of autism.
Genetic factors. In the last five years, scientists have identified a series of rare genetic changes or mutations associated with autism. They have already identified over 100 genes connected to the risk of autism. However, there is not just one mutation in the majority of cases but rather a complex and variable combination of environmental and genetic risk factors which have an influence over early brain development.
The most significant risk factor is having one or more relatives with ASD. Hence the risk of having a second child with ASD is around 20%; 10 to 20 times more than in the general population. And this possibility increases even further (up to 50%) if more than one sibling is already affected by ASD. In the case of identical (monozygotic) twins who share the same genetic material, there is a 60% possibility that they would both have ASD, but this increases to 90% in the presence of a significantly impaired capacity for social interaction.
Autism is not caused by bad parenting and the medical community considers it to be a biological disorder.
Environmental factors. These may play a role before and during childbirth. Those with the greatest evidence of an increased risk of autism are:
Advanced age of parents at the time of conception (both the mother and the father).
Illnesses suffered by the mother during pregnancy that trigger important immune responses.
Complications during childbirth, particularly any that involve a reduction in the oxygen supply reaching the baby’s brain.
Treatment for epilepsy (treatment with valproic acid during pregnancy).
Exposure to high levels of pesticides or air pollution in pregnant women.
Among the environmental factors, vaccines have been ruled out as a risk factor for autism.
It is important to remember that these factors alone do not cause autism. Only when they are combined with genetic risk factors may they produce a modest increase in risk.
Although the causes of autism are complex and have yet to be fully elucidated, there is no doubt whatsoever that it is not caused by bad parenting and the medical community considers it to be a biological disorder.