The first hint that brain damage caused by the human version of mad cow disease could be reversed has emerged from a study by British scientists.

Mice showing early symptoms of the devastating brain condition have been restored to health and normal behaviour by a new approach to therapy developed by the Medical Research Council Prion Unit in London.

The promising experiments suggest that it will be possible to treat variant Creutzfeldt-Jakob disease (vCJD), the human form of bovine spongiform encephalopathy (BSE), provided that it is diagnosed early enough.

BSE and vCJD are thought to be caused by abnormal versions of proteins, known as prions, that progressively kill off brain tissue to create characteristic “spongy” holes. When normal prions are exposed to these rogues, they contribute to the disease.

The new approach to treatment involves blocking production of normal prions, which do not appear to play a key biological role in the body, to deny the disease the raw material that it needs to kill brain cells.

In a study led by Giovanna Mallucci, the unit created genetically engineered mice that were programmed to stop producing normal prions at the age of 9 weeks.

The brains of transgenic and normal mice were injected with disease-causing rogue prions.

Both sets of mice began to show preliminary symptoms of the disease, losing the ability to recognise familiar objects and changing their behaviour patterns, particularly while feeding.

Once the GM mice reached nine weeks of age and their bodies stopped making normal prions, they began to behave normally again, and recovered the ability to learn and remember.

The normal mice, however, continued to degenerate and eventually died.

The results are published in the journal Neuron.

Dr Malucci said: “This research suggests that naturally occurring prion protein is a valid target for therapy that aims to reverse the early symptoms of prion disease and stop these diseases from progressing.”

Although human beings could not be similarly genetically engineered, the experiment’s results suggest two new approaches to therapy.

The most promising is to develop a drug that would bind to the normal prion protein and neutralise it, so that it cannot be converted into the dangerous abnormal form.

It may also be possible to develop a gene therapy in which a modified virus switch-es off the gene responsible for making normal prions, though it is likely to be hard to achieve this efficiently in an organ as large as the human brain.

Dr Mallucci said that either approach would rely on a good test for the early stages of vCJD, as once brain cells have been extensively killed off it is not possible to revive them.

“Timing is critical,” she said. “We need to target cells that are malfunctioning, but that are not yet dead.”

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