Jeremy Laurance: The biggest puzzle is the rise in cases in the past 30 years

Autism is a condition that exerts a grip on the public imagination like no other. It disturbs something that is core to our being human. In the social world in which we live, the capacity to read situations and respond appropriately is crucial to successful human interaction. People with autism lack this capacity and are confined to a lonely and isolated world as a result.

The biggest puzzle about autism is the huge rise in cases, up 12-fold among children in the past 30 years, according to some estimates. A study by Professor Simon Baron-Cohen and colleagues of the Autism Research Centre at Cambridge University, published in the British Journal of Psychiatry in May 2009, suggested that the number of children affected may be up to 50 per cent higher than previous estimates, with as many as 250,000 undiagnosed.

However, the authors dismissed suggestions that changes in lifestyle or the environment were behind the rise. They put it down to improved awareness and detection, and the inclusion of milder conditions within the diagnosis. Most experts agree it is hard to tell whether there is a genuine rise in autism. Classic autism, the severest kind, is thought to affect 30,000 people in the UK, about five in every 10,000, a figure that has remained largely unchanged in 50 years. However, more than 500,000 are estimated to be suffering from autistic spectrum disorders including Asperger's syndrome, a mild version of autism sometimes called "mind blindness".

First identified in 1943, autism has attracted increased interest in the past decade. Some suggest this is because, compared with other disorders such as Down's, people with autism look "normal" and are easier to identify with. With its defining symptom being "an inability to read social situations", it is not simple to diagnose. The disorder is known to run in families, indicating a strong genetic component, which appears confirmed in today's report in Nature. Many environmental causes have been cited, including diet, pesticides, infections, mercury and lead. But none has been identified as a definite cause. The condition has become controversial over the last 10 years because of a claimed link with the MMR vaccine – introduced in 1988 – which has since been discredited.

A second puzzle is whether autism can be treated. Many parents of autistic children believe so. Some swear that following wheat-free or milk-free diets improves symptoms. Many parents have also tried intensive one-to-one behavioural therapy for their autistic children. But the approach is still controversial.

Initial results from a small trial of a drug in people with fragile X syndrome – a genetic disorder – and autism, suggest it may improve social skills, including communication and sociability. The results for the drug arbaclofen were presented at the International Meeting for Autism Research in Philadelphia last month by Seaside Therapeutics.

The third puzzle is over a diagnostic test for autism: there isn't one. Scientists from Imperial College, London, announced last week they were working on a urine test, based on an altered "chemical fingerprint" in the urine of children with the condition. Last year, Professor Baron-Cohen announced he had moved a step closer to developing a pre-natal test based on the discovery of high levels of testosterone in the amniotic fluid surrounding the foetus. That raised the possibility that an amniocentesis test, similar to that performed for Down's syndrome, could be offered to mothers in the future. But neither test is imminent.