What is autism?

The National Autistic Society calls it "a lifelong developmental disability that affects the way a person communicates and relates to people around them". It is a spectrum, not a single disorder, involving "a triad of impairments": difficulties with social communication, social interaction and social imagination. People with autism cannot "read" other people in the way most adults come to do. They do not understand body language or facial expressions and may take jokes literally. Some may not speak, but communicate through gestures. They may stand too close or say things that seem rude or out of place. They may not be able to put themselves in another's person's shoes or predict what their companion will say or do next.

How is it diagnosed?

It may be detected in toddlers by parents or health workers when the child does not achieve the usual developmental milestones. Children will have significant problems with language, social interaction and behaviour. Later they will probably have learning difficulties, which may be associated with other problems too, such as attention deficit hyperactivity disorder (ADHD). Children with Asperger's syndrome, however, which is on the spectrum, usually have high intelligence although they may not understand jokes or figures of speech. Some "autistic savants" may become gifted mathematicians or artists.

What are the treatments?

There are no drugs that will help, but children will benefit from care and support at school and at home.

Is there an autism epidemic?

Over the last two decades the number of diagnoses has climbed. There are currently half a million people with an autism spectrum disorder in Britain. While there have been claims of links to environmental changes, most experts believe the rise in cases is down to better recognition of the disorder, which now includes children who may have been labelled "slow" or "painfully shy" in the past.