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Diagnosis

Brain protein 14-3-3 was a sensitive test for Creutzfeldt-Jakob disease

ACP J Club. 1997 Mar-Apr;126:45. doi:10.7326/ACPJC-1997-126-2-045

Related Content in this Issue
• Companion Abstract and Commentary: CSF proteins 130 and 131 were specific for diagnosing Creutzfeldt-Jakob disease


Source Citation

Hsich G, Kenney K, Gibbs CJ Jr, Lee KH, Harrington MG. The 14-3-3 brain protein in cerebrospinal fluid as a marker for transmissible spongiform encephalopathies. N Engl J Med. 1996 Sep 26;335:924-30.


Abstract

Objective

To assess the usefulness of the brain protein 14-3-3 as a diagnostic marker for Creutzfeldt-Jakob disease.

Design

Blinded comparison of the 14-3-3 immunoassay with clinical and pathologic confirmation of Creutzfeldt-Jakob disease.

Setting

United States.

Patients

257 patients who had a possible or an established diagnosis of transmissible spongiform encephalopathy, including Creutzfeldt-Jakob disease (n = 71); other dementias (n = 94); and other neurologic disorders, excluding those associated with brain infarction within the previous month (n = 92).

Description of test and diagnostic standard

Cerebrospinal fluid (CSF) proteins 130 and 131 (markers for Creutzfeldt-Jakob disease) were detected by 2-dimensional electrophoresis. The amino acid sequence of protein 14-3-3 was found to match that of fragments of proteins 130 and 131 and could be detected by a simple and rapid immunoassay of CSF. The diagnostic standard was diagnoses made by referring physicians using standard clinical criteria and pathologic studies. The 14-3-3 immunoassays were done by personnel blinded to the diagnoses.

Main outcome measures

Sensitivity and specificity of protein 14-3-3.

Main results

Protein 14-3-3 was detected in 68 of 71 patients with Creutzfeldt-Jakob disease. The sensitivity was 96% (95% CI 92% to 99%), and the specificity was 88% (CI 84% to 92%). {The likelihood ratio of a positive test was 8, and the likelihood ratio of a negative test was 0.05.}* Among the 94 patients with other diseases involving dementia, the specificity of protein 14-3-3 was 96% (CI 90% to 96%). The specificity increased when the 3 patients who had had brain infarction in the previous month were excluded (99%, CI 97% to 100%). For 15 CSF specimens from patients with Creutzfeldt-Jakob disease, electrophoretic assay was done for proteins 130 and 131 and was compared with immunoassay for protein 14-3-3. Results of the test for proteins 130 and 131 were positive for 13 samples, and results of the protein test 14-3-3 were positive for all 15 samples. The specificity of the tests was the same for dementias not associated with Creutzfeldt-Jakob disease or other neurologic disorders.

Conclusion

Brain protein 14-3-3 was a useful marker in the diagnosis of Creutzfeldt-Jakob disease.

Source of funding: U.S. Public Health Service.

For article reprint: Dr. C.J. Gibbs, Laboratory of Central Nervous System Studies, Basic Neurosciences Program, Division of Intramural Research, Building 36, Room 4A05, 9000 Rockville Pike, Bethesda, MD 20892-4122, USA.

*Numbers calculated from data in article.


Commentary

What does the practicing clinician need to know about the transmissible neurodegenerative diseases caused by prions? Prions, or proteinaceous infectious particles, are not viruses. They are smaller than viruses and are resistant to the usual methods that inactivate nucleic acids. They do not induce an immune response. The gene encoding for the human prion particle has been identified on the short arm of chromosome 20. Yet to be determined is the normal function of human prion protein in cellular metabolism or the mechanism of transformation of this protein to its pathologic isoforms and the subsequent clinical expression of neurodegenerative disease (1).

In humans, prions are responsible for Creutzfeldt-Jakob disease and the recently important bovine spongiform encephalopathy (BSE) found in cattle in Great Britain. 10% of cases of Creutzfeldt-Jakob disease can be familial and can be transmitted by an autosomal dominant pattern related to a point mutation of the encoding gene. Evidence exists for a protective effect of heterozygosity of the prion protein gene against the more common sporadic form and the fearsome iatrogenic transmission. Accidental spread by contaminated corneal transplants and neurosurgical grafting procedures has been well documented. Cadaveric sources of growth hormone and human gonadotropins have also been described as sources of the disease.

Clinically, Creutzfeldt-Jakob disease is characterized by rapidly evolving dementia, myoclonus, and a highly suggestive EEG pattern. Pathologic features are a severe loss of neurons, vacuolization, and an absence of inflammatory cells. It is intriguing how Creutzfeldt-Jakob disease prions aggregate to form amyloid filaments and plaques.

A definitive diagnosis of Creutzfeldt-Jakob disease still depends on histologic examination of brain tissue. Recently reported cases of a variant of Creutzfeldt-Jakob disease (absence of the periodic sharp-wave complexes on EEG) and its potential link to BSE have increased the urgency for a rapid and easily applied method with which to diagnose Creutzfeldt-Jakob disease (2). An accurate and practical premortem diagnostic test would be useful in identifying Creutzfeldt-Jakob disease for organ and blood donation screening. Zerr and colleagues have modified a previously described method with which to confirm and further define the sensitivity and specificity of testing for the concentration of 2 proteins (130 and 131) in the CSF of affected patients by 2-DE.

Hsich and colleagues have been able to use the simpler and more practical immunoassay of 14-3-3 proteins. They first showed that proteins 130 and 131 in CSF are in fact 14-3-3 proteins. They then showed an 88% specificity (which improves to 99% when patients with recent strokes and herpes encephalitis are excluded) of the immunoassay in the diagnosis of Creutzfeldt-Jakob disease. In animal studies, the overall specificity was an impressive 99%.

Hence, we now have an accurate CSF immunoassay to help diagnose transmissible spongiform encephalopathy in animals and humans. However, a clinical caveat is that 14-3-3 proteins may represent leakage from neuronal disruption of any cause (e.g., strokes or encephalitis); therefore, in patients with other neurologic disorders, clinical interpretation must be done with this in mind.

Clinicians may find this immunoassay useful in the proper clinical setting. Classic Creutzfeldt-Jakob disease may not be a diagnostic dilemma. However, in atypical cases, a positive immunoassay of 14-3-3 proteins may help to diagnose Creutzfeldt-Jakob disease. If it is shown that a breach can occur in the species barrier that prevents the transmission of BSE between cattle and humans, the most practical application of immunoassay of protein 14-3-3 may be to identify diseased animals and humans who are exposed to BSE.

Charles V. Guida, MD
Southampton HospitalSouthampton, New York, USA

Charles V. Guida, MD
Southampton Hospital
Southampton, New York, USA


References

1. Prusiner S. Molecular biology of prion disease. Science. 1991;252:1515-22.

2. Collinger J. New diagnostic tests for prion disease. N Engl J Med. 1996;335:963-5.