The exact cause of autism is still being investigated. However, research suggests that a combination of factors - genetic and environmental - may account for changes in brain development.
Autism is not caused by a person's upbringing, their social circumstances and is not the fault of the individual with the condition.
Boys are four times more likely to be diagnosed with autism than girls.
In total more than half a million people in the UK have an autism spectrum disorder.
Autism affects people of all racial, ethnic and socio-economic backgrounds.