Introduction to autism spectrum disorder

Autism spectrum disorder (ASD) is a lifelong neurodevelopmental condition with onset during the early developmental period. Autism spectrum disorder affects the way a person communicates with others and interacts with their environment—see Clinical characteristics. Autism is a spectrum disorder, which means that people with this condition can have very different abilities and challenges; many people with autism spectrum disorder have uneven profiles of abilities.

Autism spectrum disorder is likely to have multiple causes. Twin studies strongly support genetic factors as a cause. An identified genetic condition (eg fragile X syndrome, tuberous sclerosis) is associated in 10 to 37% of cases of autism spectrum disorder. There is no evidence to support theories that immunisation or parenting style cause autism spectrum disorder. Specific evidence that autism spectrum disorder is caused by environmental factors (eg air pollution) is limited.

Around 1% of the population has an autism spectrum disorder, with estimates ranging from one in 70 to one in 150. Estimating prevalence of autism spectrum disorder is complicated by under-recognition and under-diagnosis in adults. More children with autism spectrum disorder are presenting to services. This may reflect an increase in incidence, but is more likely due to improved case finding. Autism spectrum disorder is more common in males (3:1 ratio), but it is increasingly recognised in females and presents differently (see Clinical characteristics).

Children with autism spectrum disorder do not grow out of it, but their presentation changes and may improve with age. Development of epilepsy in adolescence can compromise progress. Outcome depends on IQ and the development of language abilities and social skills. The best outcomes are seen in people with autism spectrum disorder with an IQ in the normal range who have spoken language by the age of 5 years.