Science recreates mad cow disease

The prion proteins spontaneously caused disease

US scientists have made a protein that can trigger a neurological disorder similar to mad cow disease in mice.

The study confirms that certain forms of proteins, called prions, are infectious and are alone sufficient to cause disease, say the authors.

As well as offering insight into CJD, the human version of mad cow disease, it could shed light on Alzheimer's and Parkinson's disease, they believe.

The University of California findings appear in Science.

Dr Stanley Prusiner and colleagues produced harmless prion protein fragments in bacteria.

This is an important step in understanding the nature of prion diseases A spokeswoman from the Alzheimer's Research Trust

They folded the proteins into larger, abnormally shaped structures called amyloid fibrils and injected these into the brains of mice.

These mice began to show signs of neurological disease.

When the researchers carried out post-mortem examinations of the mice, they found the amyloid form of the prion protein, similar to those thought to cause prion diseases like Creutzfeldt-Jacob disease (CJD), in the brains of the diseased mice.

The researchers then injected healthy mice with small samples from the diseased mice brains. The healthy mice developed similar symptoms.

The prions appeared to convert other harmless prions to the abnormal disease-causing type, without needing any genetic material like DNA.

Conventional infectious agents like viruses and bacteria contain genetic material.

Infectious proteins

Co-researcher Dr Giuseppe Legname said: "A great deal of evidence indicates that prions are composed only of protein, but this is the first time that this has been shown in mammals."

Professor Moyra Bruce, group leader at the Institute for Animal Health, said: "This has been debated for years. The unusual thing about this group of diseases would be if it is just a protein and there is no genetic material involved.

"This would set them apart from all other infectious organisms that we know about. It raises all sorts of questions about how a protein could do this."

But she said the research would need to be repeated to confirm the findings.

She said contamination with infectious agents handled in the same laboratory might have caused the result.

According to the researchers, their discovery should help explain how the sporadic form of CJD, responsible for 85% of cases of prion disease in humans, develops spontaneously.

Dr Prusiner said: "We now have a tool for exploring the mechanisms by which a protein can spontaneously fold into a shape that causes disease."

He hoped the findings would also help scientists investigating other neurodegenerative diseases that involve protein misprocessing such as Alzheimer's and Parkinson's disease.

A spokeswoman from the Alzheimer's Research Trust said: "This is an important step in understanding the nature of prion diseases, such as mad cow disease and the human disease, Creutzfeldt-Jakob disease.

But she said it was less relevant to more common diseases of brain degeneration, such as Alzheimer's disease.

"The more common (sporadic) forms of Alzheimer's are caused by multiple factors and the misfolded proteins involved are not infectious," she said.