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The largest ever genetic study into autism has identified many more new genes involved in the disorder.

Oxford researchers writing in the journal Nature hope now to establish whether genetic tests can help in making early diagnosis.

The team also say the discovery of new genes should help in the identification of drugs to combat symptoms.

It is thought that about half a million people in Britain have autism to varying degrees.

Many are able to lead relatively normal lives while others require support throughout. Those with the condition find it difficult to socialise and communicate with others.

It has been known for some time that autism has a strong genetic influence - but up until now only eight or nine genes have been confirmed as playing a role.

Researchers using a new systematic analysis technique identified faults in many more regions of DNA in the 1,000 patients involved in the study. They say they might eventually find up to 300 genes which are involved.

Some of the newly identified genes play a role in developing connections between brain cells, while others are involved in sending signals within brain cells.

The study should help identify precisely which parts of the brain fail in patients.

According to one of the researchers involved, Professor Tony Monaco of Oxford University, this could help in the development of new drugs to ease some of the symptoms of autism, particularly in severely ill patients.

"We do hope to start working with pharmaceutical companies. One hope is that drugs that they might have already developed for other purposes could be used because they have a role in autism."

The researchers have identified these new regions of DNA in a fifth of the patients they have studied. They believe they will find many more genes in the remaining patients as they analyse their DNA with more sensitive methods.

The team hopes to catalogue all the genes involved in autism within the next two years.

The discovery of so many genes which all play a small part in the disease may help explain why the disorder manifests itself differently in individuals. Each person has a unique combination of faulty genes.

The study also raises the prospect of developing genetic tests to identify susceptibility to autism at an early stage. Researchers at Oxford and Newcastle are now applying for funding to carry out a pilot study on 1,000 newly diagnosed children to see if such a genetic test would be useful.

According to Professor Monaco: "The idea is to track these genes in their families and see if we can offer genetic counselling and what information we can offer the patient. If we can show the efficacy of that in the clinical care of the patients then we can push for it into genetic testing in the NHS."

"We'd hope that within two years we'd come up with clinical practice guidelines. So families can expect that we might be able to offer in the very near future some further DNA analysis of all patients."

But Dr Gina Gomez de la Cuesta of The National Autistic Society is more cautious.

She says: "This study furthers our understanding of genetic variation in autism, however there is a great deal more research to be done. Research into autism is constantly evolving but the exact causes are as yet still unknown.

"The difficulty of establishing gene involvement is compounded by the interaction of genes with the environment. Genetic testing for autism is still a long way off, given that autism is so complex.

"Whilst it is very important that research continues, it is also crucial that those living with the condition have access to appropriate advice and information, as the right support at the right time can make an enormous difference to people's lives."