James Wilkinson reports: "A significant step towards understanding the disease"

The breakthrough is a major step forward for the future development of new diagnostic tests and possibly even effective treatments of the fatal diseases.

"It opens up new research directions to understand CJD and BSE," said the research leader, Professor John Collinge, Director of the UK's Medical Research Council's Prion Unit.

Professor John Collinge explains the breakthrough

"While it leads to the possibility of developing much better diagnostic tests, our eventual goal of an effective treatment for these devastating brain diseases still remains an enormous challenge," he added.

In Britain, 39 people have died of CJD. But the incubation period may be as long as 30 years, meaning the final extent of the disease cannot yet be predicted. A blood test for CJD could reveal this.

Sharp rise in cases

The research breakthrough comes in the same week that a sharp rise in confirmed cases (nine) and referrals of CJD were announced for the last quarter of 1998.

Professor John Collinge: "epidemic entirely possible"

Simon Cousens of the CJD Surveillance Unit said the new cases were cause for concern, but said it was important to wait until the end of the year to see if they represented a trend.

Professor Collinge agreed the rise was worrying and that it was "too early to know what the figures mean". But he added that it was still entirely possible that there could be a CJD epidemic.

Deadly transformation

His new research has unmasked the mysterious mechanism by which normal prion proteins in the brain are transformed into a different, deadly form.

The rogue prion protein

This happens when a rogue prion corrupts a perfectly normal prion, PrP, which usually sits on the surface of brain cells.

It is believed that the abnormal prion causes the normal protein to change shape to form a new rogue prion. A domino effect follows.

The altered proteins cannot dissolve as normal and build up in hard clumps or "plaques". This kills the cells they form in and is also a barrier to scientific analysis of the rogue protein's structure.

The protein clumps are the "holes" which characterise the prion brain diseases and cause the brain damage which is ultimately fatal.

The normal prion protein

But just how the prion persuades the normal protein to change was until now completely unknown. Catching the conversion in the act allowed the British scientists to discover that just one, subtle change is responsible.

Single bond

"We now know that the conversion involves breaking a single bond in the molecule using conditions which exist normally within cells," explains Professor Collinge.

"This remarkable property of prion protein is unprecedented: no other protein has yet been shown to be able to exist in two such entirely unrelated shapes."

The team was convinced they had exposed the disease's secret when their altered protein formed clumps which were indistinguishable from the rogue form found in the brain of CJD and BSE victims.

New drugs

The scientists believe the new information should make it possible to create antibodies which detect the rogue protein specifically. This would mean new diagnostic tests for prion disease in humans and animals.

Also, knowing how the switch from normal to rogue protein occurs could help researchers develop new drugs to treat and prevent prion disease.