Diagnostic biomarker

A diagnostic biomarker refers to a biological parameter that aids the diagnosis of a disease and may serve in determining disease progression and/or success of treatment. It may be a laboratory, radiological, genetic, anatomical, physiological or other finding that helps to differentiate one disease from others. In 2001, the World Health Organization (WHO), in coordination with the United Nations and the International Labor Organization, has defined a biomarker as “any substance, structure, or process that can be measured in the body or its products and influence or predict the incidence of outcome or disease.” The Biomarkers Consortium, a major public-private biomedical research partnership, uses the 2001 National Institutes of Health Biomarkers Definitions Working Group definition: "Biomarkers are characteristics that are objectively measured and evaluated as indicators of normal biological processes, pathogenic processes, or pharmacologic responses to therapeutic intervention."

Presently, ME and CFS patients are diagnosed based on well-defined clinical criteria, for example, please see the Proposed Diagnostic Criteria Chart section of the Institute of Medicine report. Diagnosis also includes a process of exclusion of other causes of fatigue which can result in a delay of diagnosis.

Potential diagnostic biomarkers for ME/CFS are being explored by many researchers in the field. Below is a list of some that have been considered.

Short QT interval
"Automated measurement of QTc [QT corrected] in clinical practise has potential utility as a diagnostic biomarker in CFS."

The electrocardiographic QT interval is shorter in patients with ME/CFS than those of the general population. The only exception is in those who have a rare genetic illness, Short QT syndrome. Differentiation is easy to determine because those with Short QT syndrome also have tall and peaked T waves, whereas the T waves are normal in PwME. Modern computer-based ECG machines are programed to correct the QT interval in relation to heart rate, because a number of medical conditions illicit a prolonged QT interval.

Obstacles for use: medical personnel education needed to recognize this finding on the EKG finding as indicative of ME/CFS; modern computer-based EKG machine needed.

Natural killer cell function
Numerous studies of Chronic Fatigue Syndrome have found evidence of reduced natural killer cell function. Some studies have showed natural killer cell function correlates with illness severity. One study found increased differentiation in NK cells.

Obstacles for use: Specialized lab equipment not available in average laboratories; blood specimen must be tested within 48 hours of draw and must remain at between 59°-98.6°F or 15°-37°C so special considerations are needed in transporting blood specimens to specialized labs.

Two-day cardiopulmonary exercise testing
Two-day cardiopulmonary exercise testing or 2-day CPET is an accepted, reliable test for post-exertional malaise (PEM), one of the cardinal symptoms that distinguishes between individuals with and without ME/CFS.

Obstacles for use: The 2-day CPET "carries substantial risk for these patients as it may worsen their condition." A single day CPET is a common test used as a cardiac stress test and therefore the equipment is widely available at medical centers, however, medical personnel would need to be educated on how to interpret a 2-day CPET test for ME/CFS diagnosis.

Brain imaging
Using advanced brain imaging, Zeineh, et.al., found that there was right arcuate fasciculus (FA) abnormality in CFS patients. "Bilateral white matter atrophy is present in CFS...Right hemispheric increased FA may reflect degeneration of crossing fibers or strengthening of short-range fibers. Right anterior arcuate FA may serve as a biomarker for CFS."

Obstacle for use: The specialized radiological equipment needed for this test is usually only available in facilities engaged in research.

Chronic cell danger response state
Naviaux, et al, at the University of California, San Diego School of Medicine reported in 2016 "that targeted, broad-spectrum metabolomics of plasma not only revealed a characteristic chemical signature but also revealed an unexpected underlying biology."

Obstacle for use: The specialized laboratory equipment needed for this test is usually only available in facilities engaged in research.

Cytokine expression
Several researchers are exploring if cytokine expression in ME/CFS is a unique enough signature to be used as a diagnostic marker.

Cytokine expression changes in ME/CFS related to length of illness, with some cytokines levels increasing and some decreasing dependent on illness duration. Russell, et al, focused on a subset of three cytokines, IL-1α, 6 and 8, in plasma samples and concluded that: "Setting these 3 markers as a triple screen and adjusting their contribution according to illness duration [the] sub-groups produced ME/CFS classification accuracies of 75–88%."

Obstacle for use: Since cytokine expression changes in ME/CFS related to progression of the illness, the validity of potentially useful markers may be obscured by such variation.

MicroRNA (miRNA)
Very simply stated, microRNA (miRNA) are molecules involved in gene expression. They are different from mRNA which stands for messenger RNA. A 2016 study by Petty, et al found that "four upregulated miRNA were suitable markers to resolve CFS/ME subjects from a matched control cohort." A 2012 study by Brenu, et al found the expression of eight specific miRNAs "significantly decreased in NK cells of CFS/ME patients in comparison to the non-fatigued controls" and one specific miRNA was significantly downregulated in "both the NK and CD8(+)T cells in the CFS/ME sufferers."

In 2015, Griffith University filed for a patent for a biological marker (Patent Publication number WO2016023077 A1) for the diagnosis and management of ME and CFS. Sonya Marshall-Gradisnik and Ekua Brenu are listed as the inventors. The patent application states: "The present invention resides broadly in the use of at least one miRNA as a biological marker for identifying or diagnosing a subject having CFS and/or ME."

Obstacle for use: Although the science of using the detection of different miRNAs for disease confirmation is exploding, it is still in its infancy. There are no established baseline data for miRNAs among normal individuals which would be necessary for using miRNA levels as biomarkers. The findings in the study published in March 2016 need to be validated through replication by other studies. The Griffith University test has not been released for public use to date.

Plasma neuropeptide Y
Plasma levels of neuropeptide Y (NPY), a neurotransmitter in high quantity in the brain, are reported to be elevated in complex multi-symptom illnesses associated with immunologic dysfunction. Fletcher, et al, did a study believed to be "the first in the CFS literature to report that plasma NPY is elevated [in ME/CFS] compared to healthy controls and to a fatigued comparison group, GWI [Gulf War Illness] patients. The significant correlations of NPY with stress, negative mood, general health, depression and cognitive function strongly suggest that this peptide be considered as a biomarker to distinguish subsets of CFS."

Obstacles in use: NPY is elevated in other immune illnesses such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). NPY varies greatly between individuals and is interdependent on other cellular and molecular components and must be viewed with data from other biomarkers.

Proteome in cerebrospinal fluid
Analysis of the proteome (complement of proteins) in cerebrospinal fluid specimens by Baraniuk, et al, in 2005, showed one, consistent CFS-related proteome compared to a group with Gulf War Illness and to controls. They found the presence of 10 proteins in cerebrospinal fluid that were shared by patients with CFS, but were not detected in control samples."

A similar study of proteome analysis of cerebrospinal fluid was done in 2011 by Schutzer, et al. His group compared the pooled cerebrospinal fluid specimens of patients with chronic fatigue syndrome to patients with Neurologic Post Treatment Lyme disease (nPTLS) and to healthy controls. The cerebrospinal fluid proteome of the three groups were markedly unique for each group. Although nPTLS and CFS have similar clinical presentations, the researchers were able to distinguish the two syndromes from each other via data analysis.

Obstacles in use: The specialized laboratory equipment needed for this test is usually only available in facilities engaged in research. The samples were pooled specimens. The presence of these proteins in one patient may be too small for average laboratory equipment to detect. Specific proteins to be used for a biomarker have not been identified.

Dysfunction of TCA and urea cycles
A 2016 study in Japan, by Yamano, et al, looked at the differences in intermediate metabolite concentrations in the tricarboxylic acid (TCA) and urea cycles in CFS patients versus healthy controls: "CFS patients exhibited significant differences in intermediate metabolite concentrations in the tricarboxylic acid (TCA) and urea cycles. The combination of ornithine/citrulline and pyruvate/isocitrate ratios discriminated CFS patients from healthy controls, yielding area under the receiver operating characteristic curve values of 0.801 (95% confidential interval [CI]: 0.711–0.890, P < 0.0001) and 0.750 (95% CI: 0.584–0.916, P = 0.0069) for training (n = 93) and validation (n = 40) datasets, respectively. These findings provide compelling evidence that a clinical diagnostic tool could be developed for CFS based on the ratios of metabolites in plasma."

Obstacle for use: The specialized laboratory equipment needed for this test is usually only available in facilities engaged in research. The findings in this published study need to be validated through replication by other studies.

Combination of M-wave, TBars, and CD26
A 2016 study in France by Fenouillet, et al, examined 36 ME/CFS cases and 11 healthy controls with regard to three biological variables: a) post-exercise M-wave - a measurement after electrical stimulation of muscle nerves which coordinates with muscle fatigue b) TBARS variations - a plasma marker which represents excessive oxidative stress response to exercise, and c) CD26-expression at rest - a protein potentially related to inflammation, which was found to decrease in CFS patients. Although the researchers set out to explore physiological and biological abnormalities that could be indicative of the etiology, "striking differences" in the results between patients and controls lead them to believe that this combination could be used to identify patients with ME/CFS and help to distinguish ME/CFS patients from fibromyalgia patients.

Obstacle for use: The findings in this published study need to be validated through replication by other studies.

Others
Other biomarkers being researched:
 * the presence of salivary Human herpesvirus 6 (HHV6) and Human herpesvirus 7 (HHV7) biomarkers to distinguish physiological fatigue from pathological fatigue
 * visible and near-infrared (Vis-NIR) spectroscopy of patients' thumbs are being explored in Japan as a non-invasive test for CFS
 * Dr. David Kaufman of the Open Medicine Institute reports diagnostic markers for ME/CFS include low natural killer cell function, low vasopressin levels, mutations of the MTHFR gene, and abnormalities of the HPA axis See Arginine vasopressin

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 * 2012, Biomarkers for chronic fatigue.