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Interpretive Handbook

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Test 82528 :
14-3-3 Protein, Spinal Fluid

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

The 14-3-3 proteins are a group of highly conserved proteins composed of several isoforms that are involved in the regulation of protein phosphorylation and mitogen-activated protein kinase pathways. They exist in vivo as dimers of the various isoforms with apparent molecular mass of 30 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis and 60 kDa on gel chromatography. Sequence homology among the various isoforms ranges from 22% to100%. The beta, gamma, and theta isoforms are found in tissues of the nervous system.

 

Detectable 14-3-3 protein in the cerebrospinal fluid (CSF) is indicative of substantial, relatively rapid neuronal destruction. Increased CSF concentrations of 14-3-3 proteins have been described in patients with various forms of Creutzfeldt-Jakob disease (CJD), some other rapidly progressive dementias, and a large range of other vascular, inflammatory, neoplastic, and metabolic central nervous system (CNS) disorders (see Cautions), which can be associated with significant and rapid neuronal destruction.  

 

The main clinical use of 14-3-3 measurements is in the differential diagnosis of dementia, in particular to distinguish CJD and its variants from other dementias. The most common forms of dementia (progressive multi-infarct dementia and Alzheimer disease) are uncommonly associated with elevated CSF levels of 14-3-3, presumably because of their slow pace of progression.

 

CJD is an incurable neurodegenerative disease caused by accumulation of self-catalytically malfolded endogenous prion proteins in the CNS. Its cause is most commonly sporadic, but it can be inherited (mutations that predispose to malfolding) or acquired (iatrogenic transmission by infected human tissues or tissue extracts or surgical procedures, or by ingestion of some animal products that contain malfolded prion proteins).

 

The diagnosis of CJD is highly complex and involves clinical history and neurologic examination, electroencephalographs (EEG), magnetic resonance imaging (MRI), and exclusion of other possible causes of dementia, in addition to CSF examination. Several, slightly different scoring systems are in use to integrate these parameters into a final diagnosis of possible, probable, or definite CJD. The most widely accepted of these scoring systems is the WHO set of diagnostic criteria for sporadic CJD from 1998 (see Interpretation).

Useful For Suggests clinical disorders or settings where the test may be helpful

Evaluation of patients with rapidly progressive dementia to establish the diagnosis of Creutzfeldt-Jakob disease

Interpretation Provides information to assist in interpretation of the test results

A concentration of 14-3-3 protein in cerebrospinal fluid (CSF) of > or =1.5 ng/mL supports the diagnosis of Creutzfeldt-Jakob disease (CJD) in patients who have been carefully preselected based on various diagnostic criteria. CSF 14-3-3 measurement is particularly helpful in sporadic CJD, where it is used as 1 of several diagnostic criteria.

 

Sporadic CJD World Health Organization (WHO) diagnostic criteria from 1998:

1. Definitive CJD:

-Neuropathological diagnosis by standard techniques AND/OR immunohistochemistry AND/OR Western blot confirmed protease-resistant prion protein AND/OR presence of scrapie-associated fibrils

 

2. Probable CJD:

-Progressive dementia

-At least 2 of the following symptoms:

--Myoclonus, pyramidal/extrapyramidal, visual or cerebellar, akinetic mutism

-Positive electroencephalographs (EEG) (periodic epileptiform discharges) AND/OR positive CSF 14-3-3 protein and <2 years disease duration

-No alternate diagnosis                            

 

3. Possible CJD:

-Progressive dementia

-At least 2 of the following symptoms:

--Myoclonus, pyramidal/extrapyramidal, visual or cerebellar, akinetic mutism

-No supportive EEG and <2 years disease duration

 

Recently proposed, but not yet universally accepted, amendments to these criteria center on including magnetic resonance imaging (MRI) high-signal abnormalities in caudate nucleus and/or putamen on diffusion-weighted imaging (DWI) or fluid attenuated inversion recovery (FLAIR) as diagnostic criteria for probable CJD.

 

The USA Center of Disease Control and Prevention supports these modified WHO criteria as of 2010 (http://www.cdc.gov/ncidod/dvrd/cjd/diagnostic_criteria.html).

 

There is no established role for 14-3-3 measurement in the diagnosis of acquired or inherited CJD.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Hemolyzed specimens will be rejected. Hemolysis causes falsely-elevated 14-3-3 results. The 14-3-3 concentrations in 82 visibly blood-tinged cerebrospinal fluid (CSF) specimens were up to 281 ng/mL, with 74 specimens (90.2%) showing levels above the cutoff.

 

In addition, specimens may be determined to be unsuitable for testing if any of the following conditions are observed:(1,2)

-Macroscopically hemorrhagi

-Xanthochromic

-RBC counts >500 cells per mcL

-WBC counts >10 cells per mcL

 

The Mayo Clinic 14-3-3 assay is a quantitative assay for 14-3-3. All other assays are currently based on qualitative or semiquantitative assessment of 14-3-3 Western blots of CSF specimens. Results of diagnostic 14-3-3 studies performed in other laboratories, therefore, cannot be compared directly with the Mayo Clinic 14-3-3 test results. However, the published literature suggests comparable sensitivity and specificity ranges between the Mayo assay and Western blot assays.

 

Regardless of the method used, measurement of 14-3-3 protein in CSF should not be relied upon exclusively to establish the diagnosis of Creutzfeldt-Jakob disease (CJD). Increased concentrations of 14-3-3 protein in CSF have been described in a variety of central nervous system (CNS) diseases other than CJD that are associated with relative rapid (days to months, rather than months to years) destruction of significant amounts of CNS neuronal tissue. Published examples include: infectious encephalitides, transverse myelitis, stroke, intracerebral and subarachnoid hemorrhage, rapidly progressive vascular dementia, various metabolic and anoxic encephalopathies, severe acute CNS episodes of multiple sclerosis, cerebral vasculitides and angiopathies, mitochondrial encephalomyelopathies, CNS storage diseases, widespread or rapidly growing primary or secondary CNS and leptomeningeal tumors, and, rarely, Alzheimer disease and other primary dementias.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Normal: <1.5 ng/mL

Elevated: > or =1.5 ng/mL; compatible with, but not diagnostic of, Creutzfeldt-Jakob disease

Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Day IN, Thompson RJ: Levels of immunoreactive aldolase C, creatine kinase-BB, neuronal and non-neuronal enolase, and 14-3-3 protein in circulating human blood cells. Clin Chim Acta 1984;136:219-228

2. Collins S, Boyd A, Fletcher A, et al: Creutzfeldt-Jakob disease: diagnostic utility of 14-3-3 protein immunodetection in cerebrospinal fluid. J Clin Neurosci 2000;7:203-208

3. Preissner CM, Aksamit AJ, Parisi JE, Grebe SK: Development and validation of an immunochemiluminometric assay for 14-3-3 protein. Clin Chem 2009;55(S6):page A199; abstract D-149

4. Collins S, Boyd A, Fletcher A, et al: Creutzfeldt-Jakob disease: diagnostic utility of 14-3-3 protein immunodetection in cerebrospinal fluid. Clin Neuroscience 2000;7:203-208

5. Burkhard PR, Sanchez JC, Landis T, et al: CSF detection of the 14-3-3 protein in unselected patients with dementia. Neurology 2001;56:1528-1533

6. Aksamit AJ, Preissner CM, Homburger HA: Quantitation of 14-3-3 and neuron-specific enolase proteins in CSF in Creutzfeldt-Jakob disease. J Neurol 2001;57:728-730

7. Castellani RJ, Colucci M, Xie Z, et al: Sensitivity of 14-3-3 protein test varies in subtypes of sporadic Creutzfeldt-Jakob disease. Neurology 2004;63:436-442


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