A severe form of autism has been reversed in mice, offering the best indication yet that it could be possible to treat a condition that affects more than 10,000 children in Britain.

Rett syndrome is the most physically disabling of the autism spectrum disorders, leaving many children unable to speak, walk or use their hands, and has long been considered incurable.

It also causes breathing difficulties and primarily affects girls, 1 in 10,000 of whom has the condition.

Research at the University of Edinburgh has shown that these symptoms can be treated successfully in mice by activating a single gene which, when defective, causes Rett syndrome.

The findings, which are published in the journal Science, surprised scientists, who had not thought that restoring the MECP2 gene’s function would be a promising approach to therapy.

If it is possible to develop drugs that mimic MECP2, or the protein it produces, they could be used to treat Rett syndrome even at an advanced stage, said Adrian Bird, who led the research.

He said, however, that while the study suggested a mechanism by which a new drug may work, much more research was needed before a therapy became available.

Professor Bird discovered in 1990 that the MECP2 gene was involved in Rett syndrome, but felt that it would be difficult to treat the disease simply by improving its function.

In his most recent study, Professor Bird reactivated MECP2 in mice that had been born with the gene switched off and the symptoms of Rett syndrome.

After four weeks the mice, some of which had been close to death, recovered, becoming almost indistinguishable from normal mice, and their movement and breathing problems disappeared.

“The results we came across were entirely unexpected,” Professor Bird said.

“It had been thought that Rett syndrome is irrevocable, but our findings show that the damage to nerve-cell function is, in fact, reversible.”

Chris James, director of the Rett Syndrome Association UK, which, along with other charities, helped to fund the research with the Wellcome Trust, said: “This is a very significant step on the road to future therapeutic approaches to Rett syndrome. It will give hope to those families affected by Rett syndrome.”

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