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New CJD Test Scores High Marks
15 January 1999 7:30 pm
The United Kingdom may soon have an answer to a question that has been harrowing the country since 1996: Are the 34 cases of a fatal brain disease that is thought to be the human form of "mad cow disease" isolated occurrences, or signs of an impending epidemic? In tomorrow's issue of The Lancet, U.K. researchers report they have developed a test that can detect variant Creutzfeldt-Jakob disease (vCJD) by looking at tonsil biopsies.
So far, physicians and researchers have diagnosed the brain disorder by examining patients' brains, often after the patient had died. In 1997, however, a team led by neurologist John Collinge of St. Mary's Hospital in London found an abnormal form of the prion protein (PrP), which is the signature of vCJD, in the tonsils of a deceased patient. Since then, the team has collected a large number of lymphoid tissue samples: tonsil biopsies from 20 patients suspected of having some sort of prion disease--nine of whom were later shown to be suffering from vCJD--and tonsillectomies or stored autopsy materials taken from vCJD victims, normal controls, and sufferers of other neurological diseases, including "classic" forms of CJD not linked to mad cow disease.
Using immunohistochemistry tests, in which a target protein is "stained" with antibodies that specifically recognize it, the team found that PrP was detectable in lymphoid tissue only among vCJD sufferers and not in any of the other samples. A second test, called Western blotting, detects proteins both by their molecular weight and their reactions with antibodies; Collinge has claimed that it can distinguish different prion strains because they have different patterns of sugar residues on their surface and hence different molecular weights. The study might support that claim: Only vCJD sufferers had PrP in their lymphoid tissue, and all the vCJD patients shared the same prion strain.
The study "looks very convincing," says Oxford University epidemiologist Roy Anderson. Already, Britain's Medical Research Council and Department of Health is planning a mass screening of previously stored tonsils and appendixes, which might provide insight into the epidemic's true size. But such testing would entail difficult ethical questions: For example, with no cure in sight, should people be told they are harboring vCJD? But Collinge says a screening program is the only way for British officials to find out what they are up against. "We might find evidence of a major problem, and we need to know sooner or later."