Autism spectrum disorders (ASD)

1 April 2019 | Q&A

Autism spectrum disorders (ASD) are a group of complex brain development disorders. This umbrella term covers conditions such as autism and Asperger syndrome. These disorders are characterized by difficulties in social interaction and communication and a restricted and repetitive repertoire of interests and activities.


Reviews estimate that 1 child in 160 has an autism spectrum disorder. This estimate represents an average figure, and reported prevalence varies substantially across studies. Some recent studies have, however, reported rates that are substantially higher.


The level of intellectual functioning is extremely variable in persons with an autism spectrum disorder, ranging from profound impairment to superior non-verbal cognitive skills. It is estimated that around 50% of persons with ASD also suffer from an intellectual disability. 


Identifying an autism spectrum disorder is difficult before the age of about 12 months but diagnosis is generally possible by the age of 2 years. Characteristic features of the onset include delay in the development or temporary regression in language and social skills and repetitive stereotyped patterns of behaviour.


Parents have an essential role in providing support to a child with an autism spectrum disorder. They can help to ensure access to health services and education, and offer nurturing and stimulating environments as their child grows up. Recently, it has been shown that parents can also help deliver psychosocial and behavioural treatments to their own children.


Scientific evidence suggests that various factors, both genetic and environmental, contribute to the onset of autism spectrum disorders by influencing early brain development.


Available epidemiological data show that there is no evidence of a link between measles-mumps-rubella (MMR) vaccine and autism spectrum disorders. Previous studies suggesting a causal link were found to be seriously flawed.

There is also no evidence to suggest that any other childhood vaccine may increase the risk of autism spectrum disorders. In addition, evidence reviews commissioned by WHO concluded that there was no association between the use of vaccine preservatives such as thiomersal and autism spectrum disorders.