With Dr Hilary Cass, Consultant in Paediatric Disability, Great Ormond Street Hospital

Autism is much talked about, usually in the context of fears that it is reaching epidemic proportions in children. It is certainly true there has been an increase in the number of children diagnosed with it in the last 20 years.

In the 1980s, one child in 2,000 was diagnosed with autism. Today, this figure is one in 1,000, and at least one in 100 children have some form of broader autism spectrum disorder.

Whether this is due to better recognition, broader definitions of what autism means or a genuine change in incidence is hotly debated.

But leaving this aside, how many of us really know what autism is? Or understand how, without the right support, it can have a profound and sometimes devastating effect not only on the life of an affected child, but also those around them?

What is autism? Autism is one of a range of conditions that comes under the umbrella term "autistic spectrum". It is basically a lifelong developmental disability affecting how a person communicates with, and relates to, others. It affects four times as many boys as girls, and has no class or social barriers.

Children with autism usually experience difficulty in three main areas, to varying degrees. These areas are: social interaction (not understanding the subtleties of social situations such as how to recognise and interpret other people’s feelings and manage their own); social communication (difficulty understanding and using verbal and non-verbal language such as facial expressions) and social imagination (such as lack of creative play).

What causes it? We still do not really know. One theory is that autism is due to an abnormality in the functioning of the frontal lobes of the brain. But there is also a genetic element. If one child in a family has autism, a sibling has a three to five percent chance of also having the condition or a related problem such as a language disorder. This is a much higher rate than in the population as a whole.

What is clear is that autism is linked with some changes in brain development and research indicates that a combination of factors - genetic and environmental - may account for this.

What are the early signs and symptoms? The early signs of autism can be present under the age of one in a severely affected child. One study which looked retrospectively at videos taken during the first year of a child’s life found that a baby’s lack of response to his or her name was one of the most useful distinguishing early signs in autism. Children at the more able end of the spectrum tend to be picked up later. Although their early language development may be normal, they run into difficulties as social demands get greater, and may only present with problems when they get to school.

Is diagnosis important? Having a diagnosis is helpful because it will help a child with autism (and their family) understand why they experience certain difficulties, and it can help them access specialist services and support. A child’s GP can refer them to a specialist to make a diagnosis.

What help is available? There is, at present, no known cure for conditions on the autism spectrum, including Asperger syndrome. As the nature of autism is so complex, many interventions have been developed over the years with competing claims made for their effectiveness.