Researchers in the US have discovered that DNA is not the only prerequisite for neurological diseases such as CJD and Alzheimer's. Dick Ahlstrom reports.
Researchers in the US have created a protein that can trigger a BSE-like disease in mice. The study provides strong evidence that aberrant proteins alone can cause such neurological disorders and that genetic material is not necessary to cause these diseases.
The work was carried out by one of the world's leading BSE researchers, Dr Stanley Prusiner, and colleagues at the University of California. His findings are published in the current issue of Science.
Prusiner believes that the finding could offer insights into Creutzfeldt-Jakob disease (CJD), the human form of BSE and also other serious neurological disorders including Alzheimer's and Parkinson's diseases. The elaborate research involved engineering bacteria to produce harmless prion protein fragments.
Prions are produced naturally in mammals and are necessary for life. They are typically short-lived proteins but can be subverted to dangerous longer lasting protein forms when they encounter aberrant prion proteins.
The harmless prions were folded by the researchers into larger, abnormally shaped structures called amyloid fibrils and they injected these into the brains of mice. After a short time these mice began to show signs of neurological disease.
Later, post-mortems on the mice showed their brains contained the amyloid form of the prion protein, proof that normal prion production had been subverted. The amyloid form was similar to that associated with CJD.
Researchers then injected small brain tissue samples from the diseased mice into healthy mice. These mice also then developed neurological disease.
The researchers were particularly struck with proof that genetic material, DNA, was not necessary to cause disease. Other infectious agents such as viruses and bacteria contain genetic material, which is necessary to initiate an illness.
"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," stated co-researcher, Dr Giuseppe Legname.
"This has been debated for years," adds Prof Moyra Bruce, of the Institute of Animal Health.
"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."
The researchers believe that their discovery could help to explain how the sporadic form of CJD can develop spontaneously. The sporadic form is responsible for 85 per cent of cases of prion disease in humans.
"We now have a tool for exploring the mechanisms by which a protein can spontaneously fold into a shape that causes disease," stated Prusiner.
The findings could help scientists investigating other neurodegenerative diseases that involve the production of aberrant proteins, disorders such as Alzheimer's and Parkinson's diseases, Prusiner added.