First results of vCJD survey show no signs of prion

First results from a study of human tissues have shown no evidence of the abnormal prion protein associated with Creutzfeldt-Jakob disease.

A total of 3170 specimens of tonsil and appendix tissue were examined for traces of the protein as part of a study designed to help assess the number of cases of variant Creutzfeldt-Jakob disease (vCJD) that may be incubating in the adult UK population.

Estimates of the total number of cases have varied widely over the past few years, from half a million down to 100. So far, 53 people have died from vCJD, a disease caused by the same strain of agent as bovine spongiform encephalopathy (BSE). A further 12 people are alive with vCJD-like symptoms

Despite the negative results from this first batch of specimens, announced by the Department of Health, the chief medical officer, Professor Liam Donaldson, urged caution in their interpretation.

“The fact that no positives have been found is welcome news, but these early results should not be taken as an indication of an ‘all clear,’” he said.

“The methods of analysis used on the small sample have some limitation. In addition, we do not know at what point in the incubation period tissues, such as tonsils or appendices, could turn positive, how long the incubation period would be, or even whether any individuals who were found positive would necessarily go on to develop the disease.”

He added: “The critical gap in our knowledge remains not having a reliable diagnostic test to detect the presence of the abnormal protein at the pre-clinical stage of the disease.”

The scientific group chaired by Professor Les Borysiewicz of the University of Wales College of Medicine will eventually look at the results from studies of 18000 samples.

The first 3170 samples, analysed at the National CJD Surveillance Unit in Edinburgh and at Derriford Hospital, Plymouth, were archive material from operations that were carried out between 1996 and 1998.

The downside of working with archive material was that some more sensitive analysis techniques could not be used. An added complication was that some samples were not appropriate for analysis. Altogether, 4166 specimens were originally studied, but only 3170 were considered suitable for analysis. More sensitive tests are to be carried out on fresher material

A further complication—surrounding interpretation of the data—is that the relation between the presence of prion protein in lymphoid tissue and the subsequent onset of vCJD, although thought to be highly probable, is not proved.

Professor Donaldson said that the government was committed to spending some £26m ($42m) over the next year on research into CJD and BSE issues.