Test could improve detection of prion disease in humans
A highly sensitive post-mortem test could help scientists more accurately determine if a person died of Creutzfeldt-Jakob disease (CJD), a human neurological disorder caused by the same class of infectious proteins that trigger mad cow disease, according to a new study supported in part by the National Institutes of Health (NIH). The finding opens the possibility that such testing might be refined in the future so it can be used to detect prion disease in living people and animals before the onset of symptoms.
The test, called conformation-dependent immunoassay (CDI), was originally developed to detect various forms of disease-causing proteins called prions in cows, sheep, deer and other animals. In the new study, researchers led by Jiri Safar, M.D., Bruce Miller, M.D., Michael Geschwind, M.D., Stephen DeArmond, M.D., and Nobel Laureate Stanley B. Prusiner, M.D., of the University of California, San Francisco, found that CDI not only identifies prions in human brain tissue but is faster and far more precise than the standard immunological detection methods, which only detect a small fraction of the infectious prions that may be in the brain.
The finding appears in the March 1, 2005 issue of the Proceedings of the National Academy of Sciences, www.pnas.org. Two components of the NIH, the National Institute of Neurological Disorders and Stroke (NINDS)* and the National Institute on Aging (NIA), supported the study. Additional support was provided by the John Douglas French Foundation for Alzheimers research, the McBean Foundation, and the Alzheimers Disease Research Center of California.
"The findings of this NIH-funded research are an important step forward for the detection of prions," said Michael Nunn, Ph.D., NINDS program director for prion research. "It has been very difficult to generate diagnostic tests in this area and these results are a significant improvement for the diagnosis of CJD in living people."
In the study, Prusiner and his colleagues extracted brain tissue from 28 people who had died of CJD. They tested these samples using CDI, which uses highly specific antibodies that bind to all disease-causing prions in the brain. They also used immunohistochemistry (IHC) to measure only the prion proteins that are resistant to an enzyme called protease. Protease-resistant prions are abnormal and usually infectious, meaning they can cause CJD and other neurodegenerative diseases. CDI detected abnormal prions in all of the sampled brain regions. In contrast, the researchers found that IHC detected abnormal prions in less than 25 percent of the sampled brain regions. The findings, according to the researchers, suggest that CDI could be used to establish or rule out the diagnosis of CJD with greater accuracy than IHC, particularly when a small number of samples are available. Prusiner and colleagues are exploring the possibility of using CDI in living tissue, like blood or muscle, to detect and diagnose prion diseases, such as CJD or bovine spongiform encephalopathy (BSE, mad cow disease) while people or animals are still alive.
"This research not only is an important advance for the detection and diagnosis of prion diseases, but, with the identification of protease-sensitive infectious prions, will lead to a better understanding of the underlying disease processes," said Andrew Monjan, Ph.D., Chief of the NIAs Neurobiology of Aging Branch.
Prusiner received the 1997 Nobel Prize in physiology or medicine for his discovery of prions. Unlike viruses, bacteria, fungi, and parasites, prions contain no DNA or RNA. Instead, prions are an altered type of protein normally found within cells in humans and other organisms. These abnormal prion proteins appear to convert other, normal prions to an abnormal shape. Many scientists now believe this conversion process leads to several dementing diseases in humans, including CJD. Similar diseases in animals include bovine spongiform encephalopathy ("mad cow" disease) in cattle and scrapie in sheep. Abnormal, misfolded proteins contribute to other age-related neurological diseases such as Alzheimers and Parkinsons diseases. According to Prusiner and his colleagues, CDI testing might eventually have a role in the diagnosis of other neurodegenerative diseases, including Alzheimers and Parkinsons, in which normally shaped proteins are structurally altered.
Doug Dollemore | EurekAlert!