An astonishing discovery at the Institute of Neurology in London, UK, has revealed that a fatal brain disorder related to mad-cow disease is reversible in mice. Prion diseases — such as bovine spongioform encephalopathy (BSE or mad-cow disease), Creutzfeldt-Jakob disease (CJD) and scrapie — are caused by infection with a misfolded form of normal nerve-cell proteins known as prions. The misfolded prion converts healthy prions into copies of itself and the accumulation of abnormal proteins results in dementia and death.

Giovanna Mallucci and colleagues bred a strain of mutant mice whose nerve cells could be induced to remove normal prions. First, they infected the mice with abnormal prions and allowed the disease to develop. Then the normal prions were depleted and, surprisingly, the disease was halted and early brain damage reversed. According to Mallucci, “It's the conversion process, not the accumulation of protein, that is key to the disease” (Nature Science Update, 31 October 2003). “The conversion process might produce a toxic intermediate stage, or it might somehow cause the nerve tissue to break down” (BBC News Online, 31 October 2003).

Prion experts are excited by the breakthrough, as previous work — focusing on the abnormal prions — has been disappointing. “We missed the target ... it's not the abnormal form but the normal form of the prion protein that has to be attacked”, said Jean-Philipe Deslys from the Commission of Atomic Energy, France (Agence France-Presse, 30 October 2003). Adriano Aguzzi from University Hospital Zurich, Switzerland, claims, “This is a milestone in prion research” (Nature Science Update, 31 October 2003).