The causes of autism are still being investigated. Many experts believe that the pattern of behaviour from which autism is diagnosed may not result from a single cause.

Genetic link

Research that has been carried out with twins, and families, suggests that autism may have a strong genetic link, but the sites of relevant genes have yet to be identified. Scientists have been attempting to identify which genes might be responsible for autism for some years.

It is likely that multiple genes are responsible for causing autism, rather than a single gene. However, it is difficult to establish exactly which genes are involved because of the interaction between genes, and their interaction with environmental factors. For these reasons, at the moment, there is no way of genetically testing someone to find out whether they are likely to develop autistic spectrum disorder.

Environmental factors

Environmental factors, such as pollution and certain viruses, may play a part in autism, although their exact role is unclear. In the past it was thought that the MMR vaccine may possibly be linked to ASD, but research has shown that there is no evidence to suggest that this is the case.

In a minority of cases, there is evidence to suggest that autism, along with other developmental disorders, may be caused by a variety of physical factors, all of which affect brain development and occur before, during, or after birth. For example, maternal rubella, tuberous sclerosis, lack of oxygen at birth, and encephalitis as a complication of an infectious illness. However, autism is not caused by emotional deprivation or the way a person has been brought up.