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New test targets 'mad cow' disease
An accurate, fast and specific test to detect Creutzfeldt-Jakob disease, often referred to as "mad cow disease", has been developed, paving the way for better diagnosis of the fatal condition.

The new test, developed by a Japanese team in collaboration with Australian researchers, is reported today in a paper published in Nature Medicine .

It's hoped the new tool will reduce unnecessary invasive testing of people suspected of having the disease, says co-author Associate Professor Steven Collins, director of the Australian National Creutzfeldt-Jakob Disease Registry.

Creutzfeldt-Jakob disease is a rare and fatal degenerative brain disease of the central nervous system in humans. In its most common form, known as sporadic CJD, it affects slightly more than two in a million people, says Collins.

In the 1990s the condition became popularly known as mad cow disease, after several cases in which people who had eaten beef from cows with bovine spongiform encephalopathy contracted a variation of CJD known as vCJD.

CJD is one of a group of diseases that affects humans and animals, known as the transmissible spongiform encephalopathies (TSEs) or prion diseases.

These prion diseases are characteristically associated with the accumulation of an infectious abnormal prion protein, PrPSc in the central nervous system.

PrPSc prions cannot be broken down, and instead accumulate óclustering in brain tissue and causing it to develop a spongelike appearance.

In the paper in Nature Medicine Ryuichiro Atarashi, of the Graduate School of Biomedical Sciences at Nagasaki University, and colleagues, say their new test overcomes problems with false positives thrown up by other tests such as the 14-3-3 protein test.

Currently definitive confirmation of CJD requires the detection of PrPSc in biopsy specimens taken from people suspected of having the disease, a practice that is discouraged because of the risk of infection.
A less invasive testing technique

However Atarashi and colleagues have used a relatively simple assay, the real-time quaking-induced conversion (QUIC) test, to achieve greater specificity in diagnosis by targeting the marker protein PrPSc.

The test involves taking a sample of cerebrospinal fluid from a suspected sufferer.

Normal prion proteins are then exposed to the fluid. PrPSc is a so-called misfolded protein, which is very stable in its misfolded form and encourages other proteins to also adapt a misfolded form.

If PrPSc is present in the sample fluid, it will cause the normal proteins to misfold - a reaction that is encouraged through automated shaking of the sample.

A simple dye test over 48 hours will then show whether there is an increase in the abnormal proteins.

Atarashi says they can detect as little as one femtogram (10-15 grams) of PrPSc in the cerebrospinal fluid of people with CJD.

The work follows on from earlier US-based research by Atarashi that showed QUIC assays correctly detected CJD in hamster and sheep prion diseases.

For this latest study the team first tested cerebrospinal fluid from 18 definite cases of CJD in Japan and 35 non-CJD controls from subjects with other neurodegenerative diseases.

There were no false positives reported and the test accurately diagnosed CJD 83 per cent of the time.

A further blind study using 30 samples from the Australian National Creutzfeldt-Jakob Disease Registry again recorded no false positives and 87.5 per cent accuracy in detection of the disease.

Collins says although the sensitivity of the test is comparable to the commonly used 14-3-3 protein test, the new CJD test is "much more aligned to the actual disease".

"The hope is if we can more accurately and confidently say that the illness is CJD, then patients won't be subjected to unnecessary invasive tests," he says.

"In the short-term this knowledge will [also] help guide patient management more directly."

Collins says in the long term, when a treatment is found, the new test means it will be easier and faster to determine the appropriate people to treat.

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