UK Scientists Improve vCJD Blood Test
In a new study, UK based scientists report further advances on a blood test for variant Creutzfeldt-Jakob disease (vCJD) that was first developed in 2011. The test screens for abnormal prion proteins. The study, “Population Screening for Variant Creutzfeldt-Jakob Disease Using a Novel Blood Test Diagnostic Accuracy and Feasibility Study,” was published online March 3, 2014, in the journal JAMA Neurology. The lead author of the report was Graham S. Jackson, PhD, University College of London Institute of Neurology.
vCJD is characterized by misshapen prion proteins that form spongelike holes in brain tissue. The condition is degenerative and results in death. The majority of vCJD cases in humans occurred during an outbreak in the UK in the 1990s, after people ate beef contaminated with bovine spongiform encephalopathy (BSE). There have been 170 confirmed fatal cases of vCJD in the UK. Transmissions of vCJD via transfusions containing contaminated blood or blood products are also a growing concern. There have been five transfusion-related cases in the UK. To date, the problem for health officials has been the lack of an available diagnostic test for vCJD, which can only be confirmed via a post-mortem brain matter analysis. Further, the virus has a dormancy period that can last for years or even decades before symptoms appear.
Prions bind to some metal surfaces, including stainless steel, which the researchers used in the test. In earlier studies, investigators analyzed 190 blood samples from 21 patients with vCJD, 27 with sporadic CJD, 42 with other neurological diseases and 100 normal controls. The blood assay detected the infectious prions in 15 of the 21 vCJD samples, a success rate of 71%.
“Despite some limitations and uncertainties, our findings indicate the prototype vCJD assay is suitable for both clinical diagnostics and screening,” reported Graham.
Larger follow-up studies included 5,000 US blood donors, 200 healthy UK blood donors, 352 patients with nonprion neurodegenerative diseases, 105 patients with a likely diagnosis of prion disease, and 10 patients with confirmed vCJD. The assay was 100% specific (no false positives) among the presumed negative US donor samples and was confirmed in the healthy UK donors.Among the potentially cross-reactive blood samples from patients with nonprion neurodegenerative diseases, including Alzheimer disease and frontotemporal dementia, no samples tested positive (100% specificity). Results also displayed a high sensitivity—71.4% success rate in confirmed vCJD cases.
“The extremely high specificity supports using the assay to screen for vCJD infection in prion-exposed populations. Additionally, the lack of cross-reactivity and false positives in a range of nonprion neurodegenerative diseases supports the use of the assay in patient diagnosis,” concluded the authors.
It is anticipated that the test could be used to screen large samples of the UK population, at-risk groups, and samples from blood, organ and tissue donors.
Source: Reuters Health, March 3, 2014