Tag: biomarker

Discriminating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and comorbid conditions using metabolomics in UK Biobank

Abstract:

Background: Diagnosing complex illnesses like Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is complicated due to the diverse symptomology and presence of comorbid conditions. ME/CFS patients often present with multiple health issues, therefore, incorporating comorbidities into research can provide a more accurate understanding of the condition’s symptomatology and severity, to better reflect real-life patient experiences.

Methods: We performed association studies and machine learning on 1194 ME/CFS individuals with blood plasma nuclear magnetic resonance (NMR) metabolomics profiles, and seven exclusive comorbid cohorts: hypertension (n = 13,559), depression (n = 2522), asthma (n = 6406), irritable bowel syndrome (n = 859), hay fever (n = 3025), hypothyroidism (n = 1226), migraine (n = 1551) and a non-diseased control group (n = 53,009).

Results: We present a lipoprotein perspective on ME/CFS pathophysiology, highlighting gender-specific differences and identifying overlapping associations with comorbid conditions, specifically surface lipids, and ketone bodies from 168 significant individual biomarker associations. Additionally, we searched for, trained, and optimised a machine learning algorithm, resulting in a predictive model using 19 baseline characteristics and nine NMR biomarkers which could identify ME/CFS with an AUC of 0.83 and recall of 0.70. A multi-variable score was subsequently derived from the same 28 features, which exhibited ~2.5 times greater association than the top individual biomarker.

Conclusions: This study provides an end-to-end analytical workflow that explores the potential clinical utility that association scores may have for ME/CFS and other difficult to diagnose conditions.

Source: Huang K, G C de Sá A, Thomas N, Phair RD, Gooley PR, Ascher DB, Armstrong CW. Discriminating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and comorbid conditions using metabolomics in UK Biobank. Commun Med (Lond). 2024 Nov 26;4(1):248. doi: 10.1038/s43856-024-00669-7. PMID: 39592839; PMCID: PMC11599898.  https://pmc.ncbi.nlm.nih.gov/articles/PMC11599898/ (Full text)

Hypocapnic cerebral hypoperfusion: A biomarker of orthostatic intolerance

Abstract:

The objective of the study was to identify markers of hypocapnic cerebral hypoperfusion (HYCH) in patients with orthostatic intolerance (OI) without tachycardia and without orthostatic hypotension. This single center, retrospective study included OI patients referred for autonomic evaluation with the 10 min tilt test. Heart rate, end-tidal CO2 (ET-CO2), blood pressure, and cerebral blood flow velocity (CBFv) from middle cerebral artery were monitored. HYCH was defined by: (1) Symptoms of OI; (2) Orthostatic hypocapnia (low ET-CO2); (3) Abnormal decline in orthostatic CBFv due to hypocapnia; 4) Absence of tachycardia, orthostatic hypotension, or other causes of low CBFv or hypocapnia.

Sixteen subjects met HYCH criteria (15/1 women/men, age 38.5±8.0 years) and were matched by age and gender to postural tachycardia patients (POTS, n = 16) and healthy controls (n = 16). During the tilt, CBFv decreased more in HYCH (-22.4±7.7%, p<0.0001) and POTS (-19.0±10.3%, p<0.0001) compared to controls (-3.0±5.0%). Orthostatic ET-CO2 was lower in HYCH (26.4±4.2 (mmHg), p<0.0001) and POTS (28.6±4.3, p<0.0001) compared to controls (36.9 ± 2.1 mmHg). Orthostatic heart rate was normal in HYCH (89.0±10.9 (BPM), p<0.08) and controls (80.8 ±11.2), but was higher in POTS (123.7±11.2, p<0.0001). Blood pressure was normal and similar in all groups.

It is concluded that both HYCH and POTS patients have comparable decrease in CBFv which is due to vasoconstrictive effect of hypocapnia. Blood flow velocity monitoring can provide an objective biomarker for HYCH in OI patients without tachycardia.

Source: Novak P. Hypocapnic cerebral hypoperfusion: A biomarker of orthostatic intolerance. PLoS One. 2018 Sep 26;13(9):e0204419. doi: 10.1371/journal.pone.0204419. PMID: 30256820; PMCID: PMC6157889. https://pmc.ncbi.nlm.nih.gov/articles/PMC6157889/ (Full text)

Immunometabolic changes and potential biomarkers in CFS peripheral immune cells revealed by single-cell RNA sequencing

Abstract:

The pathogenesis of Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) remains unclear, though increasing evidence suggests inflammatory processes play key roles. In this study, single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) was used to decipher the immunometabolic profile in 4 ME/CFS patients and 4 heathy controls.

We analyzed changes in the composition of major PBMC subpopulations and observed an increased frequency of total T cells and a significant reduction in NKs, monocytes, cDCs and pDCs. Further investigation revealed even more complex changes in the proportions of cell subpopulations within each subpopulation. Gene expression patterns revealed upregulated transcription factors related to immune regulation, as well as genes associated with viral infections and neurodegenerative diseases.

CD4+ and CD8+ T cells in ME/CFS patients show different differentiation states and altered trajectories, indicating a possible suppression of differentiation. Memory B cells in ME/CFS patients are found early in the pseudotime, indicating a unique subtype specific to ME/CFS, with increased differentiation to plasma cells suggesting B cell overactivity. NK cells in ME/CFS patients exhibit reduced cytotoxicity and impaired responses, with reduced expression of perforin and CD107a upon stimulation. Pseudotime analysis showed abnormal development of adaptive immune cells and an enhanced cell-cell communication network converging on monocytes in particular.

Our analysis also identified the estrogen-related receptor alpha (ESRRA)-APP-CD74 signaling pathway as a potential biomarker for ME/CFS in peripheral blood. In addition, data from the GSE214284 database confirmed higher ESRRA expression in the monocyte cell types of male ME/CFS patients. These results suggest a link between immune and neurological symptoms.

The results support a disease model of immune dysfunction ranging from autoimmunity to immunodeficiency and point to amyloidotic neurodegenerative signaling pathways in the pathogenesis of ME/CFS. While the study provides important insights, limitations include the modest sample size and the evaluation of peripheral blood only.

These findings highlight potential targets for diagnostic biomarkers and therapeutic interventions. Further research is needed to validate these biomarkers and explore their clinical applications in managing ME/CFS.

Source: Sun Y, Zhang Z, Qiao Q, Zou Y, Wang L, Wang T, Lou B, Li G, Xu M, Wang Y, Zhang Z, Hou X, Chen L, Zhao R. Immunometabolic changes and potential biomarkers in CFS peripheral immune cells revealed by single-cell RNA sequencing. J Transl Med. 2024 Oct 11;22(1):925. doi: 10.1186/s12967-024-05710-w. PMID: 39394558. https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-024-05710-w (Full text)

Identifying microRNAs Possibly Implicated in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Fibromyalgia: A Review

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and fibromyalgia (FM) are chronic syndromes of unknown etiology, accompanied by numerous symptoms affecting neurological and physical conditions. Despite frequent revisions of the diagnostic criteria, clinical practice guidelines are often outdated, leading to underdiagnosis and ineffective treatment. Our aim was to identify microRNA (miRNA) biomarkers implicated in pathological mechanisms underlying these diseases.
A comprehensive literature review using publicly accessible databases was conducted. Interesting miRNAs were extracted from relevant publications on ME/CFS and/or FM, and were then linked to pathophysiological processes possibly manifesting these chronic diseases. Dysregulated miRNAs in ME/CFS and FM may serve as promising biomarkers for these diseases.
Key identified miRNAs, such as miR-29c, miR-99b, miR-128, miR-374b, and miR-766, were frequently mentioned for their roles in immune response, mitochondrial dysfunction, oxidative stress, and central sensitization, while miR-23a, miR-103, miR-152, and miR-320 were implicated in multiple crucial pathological processes for FM and/or ME/CFS.
In summary, both ME/CFS and FM seem to share many dysregulated biological or molecular processes, which may contribute to their commonly shared symptoms. This miRNA-based approach offers new angles for discovering molecular markers urgently needed for early diagnosis or therapeutics to tackle the pathology of these medically unexplained chronic diseases.
Source: Tsamou M, Kremers FAC, Samaritakis KA, Roggen EL. Identifying microRNAs Possibly Implicated in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Fibromyalgia: A Review. International Journal of Molecular Sciences. 2024; 25(17):9551. https://doi.org/10.3390/ijms25179551 https://www.mdpi.com/1422-0067/25/17/9551 (Full text)

Replicated blood-based biomarkers for Myalgic Encephalomyelitis not explicable by inactivity

Abstract:

Myalgic Encephalomyelitis (ME; sometimes referred to as chronic fatigue syndrome) is a relatively common and female-biased disease of unknown pathogenesis that profoundly decreases patients’ health-related quality-of-life. ME diagnosis is hindered by the absence of robustly-defined and specific biomarkers that are easily measured from available sources such as blood, and unaffected by ME patients’ low level of physical activity.

Previous studies of blood biomarkers have not yielded replicated results, perhaps due to low study sample sizes (n<100). Here, we use UK Biobank (UKB) data for up to 1,455 ME cases and 131,303 population controls to discover hundreds of molecular and cellular blood traits that differ significantly between cases and controls. Importantly, 116 of these traits are replicated, as they are significant for both female and male cohorts.

Our analysis used semi-parametric efficient estimators, an initial Super Learner fit followed by a one-step correction, three types of mediators, and natural direct and indirect estimands, to decompose the average effect of ME status on molecular and cellular traits. Strikingly, these trait differences cannot be explained by ME cases’ restricted activity.

Of 3,237 traits considered, ME status had a significant effect on only one, via the “Duration of walk” (UKB field 874) mediator. By contrast, ME status had a significant direct effect on 290 traits (9%). As expected, these effects became more significant with increased stringency of case and control definition.

Significant female and male traits were indicative of chronic inflammation, insulin resistance and liver disease. Individually, significant effects on blood traits, however, were not sufficient to cleanly distinguish cases from controls. Nevertheless, their large number, lack of sex-bias, and strong significance, despite the ‘healthy volunteer’ selection bias of UKB participants, keep alive the future ambition of a blood-based biomarker panel for accurate ME diagnosis.

Source: Sjoerd V Beentjes, Julia Kaczmarczyk, Amanda Cassar, Gemma Louise Samms, Nima S Hejazi, Ava Khamseh, Chris P Ponting. Replicated blood-based biomarkers for Myalgic Encephalomyelitis not explicable by inactivity. medRxiv 2024.08.26.24312606; doi: https://doi.org/10.1101/2024.08.26.24312606 https://www.medrxiv.org/content/10.1101/2024.08.26.24312606v1 (Full text available as PDF file)

Fast Targeted Metabolomics for Analyzing Metabolic Diversity of Bacterial Indole Derivatives in ME/CFS Gut Microbiome

Abstract:

Disruptions in microbial metabolite interactions due to gut microbiome dysbiosis and metabolomic shifts may contribute to Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and other immune-related conditions. The aryl hydrocarbon receptor (AhR), activated upon binding various tryptophan metabolites, modulates host immune responses. This study investigates whether the metabolic diversity-the concentration distribution-of bacterial indole pathway metabolites can differentiate bacterial strains and classify ME/CFS samples.

A fast targeted liquid chromatography-parallel reaction monitoring method at a rate of 4 minutes per sample was developed for large-scale analysis. This method revealed significant metabolic differences in indole derivatives among B. uniformis strains cultured from human isolates. Principal component analysis identified two major components (PC1, 68.9%; PC2, 18.7%), accounting for 87.6% of the variance and distinguishing two distinct B. uniformis clusters. The metabolic difference between clusters was particularly evident in the relative contributions of indole-3-acrylate and indole-3-aldehyde.

We further measured concentration distributions of indole derivatives in ME/CFS by analyzing fecal samples from 10 patients and 10 healthy controls using the fast targeted metabolomics method. An AdaBoost-LOOCV model achieved moderate classification success with a mean LOOCV accuracy of 0.65 (Control: precision of 0.67, recall of 0.60, F1-score of 0.63; ME/CFS: precision of 0.64, recall of 0.7000, F1-score of 0.67).

These results suggest that the metabolic diversity of indole derivatives from tryptophan degradation, facilitated by the fast targeted metabolomics and machine learning, is a potential biomarker for differentiating bacterial strains and classifying ME/CFS samples.

Mass spectrometry datasets are accessible at the National Metabolomics Data Repository (ST002308, DOI: 10.21228/M8G13Q; ST003344, DOI: 10.21228/M8RJ9N; ST003346, DOI: 10.21228/M8RJ9N).

Source: Tian H, Wang L, Aiken E, Ortega RJV, Hardy R, Placek L, Kozhaya L, Unutmaz D, Oh J, Yao X. Fast Targeted Metabolomics for Analyzing Metabolic Diversity of Bacterial Indole Derivatives in ME/CFS Gut Microbiome. bioRxiv [Preprint]. 2024 Jul 29:2024.07.29.605643. doi: 10.1101/2024.07.29.605643. PMID: 39131327; PMCID: PMC11312560. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11312560/ (Full text)

The role of clinical neurophysiology in the definition and assessment of fatigue and fatigability

Highlights:

  • Though a common symptom, fatigue is difficult to define and investigate, and occurs in a wide variety of disorders, with differing pathological causes.
  • This review aims to guide clinicians in how to approach fatigue and to suggest that neurophysiological tests may allow an understanding of its origin and severity.
  • The effectiveness of neurophysiological tests as cost-effective objective biomarkers for the assessment of fatigue has been summarised.

Abstract

Though a common symptom, fatigue is difficult to define and investigate, occurs in a wide variety of neurological and systemic disorders, with differing pathological causes. It is also often accompanied by a psychological component. As a symptom of long-term COVID-19 it has gained more attention.

In this review, we begin by differentiating fatigue, a perception, from fatigability, quantifiable through biomarkers. Central and peripheral nervous system and muscle disorders associated with these are summarised. We provide a comprehensive and objective framework to help identify potential causes of fatigue and fatigability in a given disease condition. It also considers the effectiveness of neurophysiological tests as objective biomarkers for its assessment. Among these, twitch interpolation, motor cortex stimulation, electroencephalography and magnetencephalography, and readiness potentials will be described for the assessment of central fatigability, and surface and needle electromyography (EMG), single fibre EMG and nerve conduction studies for the assessment of peripheral fatigability.

The purpose of this review is to guide clinicians in how to approach fatigue, and fatigability, and to suggest that neurophysiological tests may allow an understanding of their origin and interactions. In this way, their differing types and origins, and hence their possible differing treatments, may also be defined more clearly.

Source: Tankisi H, Versace V, Kuppuswamy A, Cole J. The role of clinical neurophysiology in the definition and assessment of fatigue and fatigability. Clin Neurophysiol Pract. 2023 Dec 18;9:39-50. doi: 10.1016/j.cnp.2023.12.004. PMID: 38274859; PMCID: PMC10808861. https://www.sciencedirect.com/science/article/pii/S2467981X23000367 (Full text)

Identification of CD8 T-cell dysfunction associated with symptoms in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and Long COVID and treatment with a nebulized antioxidant/anti-pathogen agent in a retrospective case series

Highlights:

• Both Long COVID and ME/CFS are characterized by dysfunctional CD8 T-cells with severe deficiencies in their abilities to produce IFNγ and TNFα.

• In a small Long COVID and ME/CFS case series, patients’ immune deficiency and health improve during treatment period with a nebulized antioxidant, anti-pathogen and immune-modulatory pharmacological agent.

• This work provides evidence of a useful biomarker, CD8 T-cell dysfunction reminiscent of T cell exhaustion, that may assist diagnosis and have utility for tracking disease outcome during therapy, including response to a potential new treatment.

Abstract:

Background: Patients with post-acute sequelae of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection (PASC, i.e., Long COVID) have a symptom complex highly analogous to many features of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), suggesting they may share some aspects of pathogenesis in these similar disorders. ME/CFS is a complex disease affecting numerous organ systems and biological processes and is often preceded by an infection-like episode. It is postulated that the chronic manifestations of illness may result from an altered host response to infection or inability to resolve inflammation, as is being reported in Long COVID. The immunopathogenesis of both disorders is still poorly understood. Here, we show data that suggest Long COVID and ME/CFS may be due to an aberrant response to an immunological trigger-like infection, resulting in a dysregulated immune system with CD8 T-cell dysfunction reminiscent of some aspects of T-cell clonal exhaustion, a phenomenon associated with oxidative stress. As there is an urgent need for diagnostic tools and treatment strategies for these two related disabling disorders, here, in a retrospective case series, we have also identified a potential nebulized antioxidant/anti-pathogen treatment that has evidence of a good safety profile. This nebulized agent is comprised of five ingredients previously reported individually to relieve oxidative stress, attenuate NF-κB signaling, and/or to act directly to inhibit pathogens, including viruses. Administration of this treatment by nebulizer results in rapid access of small doses of well-studied antioxidants and agents with anti-pathogen potential to the lungs; components of this nebulized agent are also likely to be distributed systemically, with potential to enter the central nervous system.

Methods and Findings: We conducted an analysis of CD8 T-cell function and severity of symptoms by self-report questionnaires in ME/CFS, Long COVID and healthy controls. We developed a CD8 T-cell functional assay, assessing CD8 T-cell dysfunction by intracellular cytokine staining (ICS) in a group of ME/CFS (n = 12) and Long COVID patients (n = 8), comparing to healthy controls (HC) with similar age and sex (n = 10). Magnet-enriched fresh CD8 T-cells in both patient groups had a significantly diminished capacity to produce both cytokines, IFNγ or TNFα, after PMA stimulation when compared to HC. The symptom severity questionnaire showed similar symptom profiles for the two disorders. Fortuitously, through a retrospective case series, we were able to examine the ICS and questionnaire data of 4 ME/CFS and 4 Long COVID patients in conjunction with their treatment (3–15 months). In parallel with the treatment pursued electively by participants in this retrospective case series, there was an increase in CD8 T-cell IFNγ and TNFα production and a decrease in overall self-reported symptom severity score by 54%. No serious treatment-associated side effects or laboratory anomalies were noted in these patients.

Conclusions: Here, in this small study, we present two observations that appear potentially fundamental to the pathogenesis and treatment of Long COVID and ME/CFS. The first is that both disorders appear to be characterized by dysfunctional CD8 T-cells with severe deficiencies in their abilities to produce IFNγ and TNFα. The second is that in a small retrospective Long COVID and ME/CFS case series, this immune dysfunction and patient health improved in parallel with treatment with an immunomodulatory, antioxidant pharmacological treatment with anticipated anti-pathogen activity. This work provides evidence of the potential utility of a biomarker, CD8 T-cell dysfunction, and suggests the potential for benefit from a new nebulized antioxidant/anti-pathogen treatment. These immune biomarker data may help build capacity for improved diagnosis and tracking of treatment outcomes during clinical trials for both Long COVID and ME/CFS while providing clues to new treatment avenues that suggest potential efficacy for both conditions.

Source: Gil, A., Hoag, G.E., Salerno, J.P., Hornig, M., Klimas, N., Selin, L.K. Identification of CD8 T-cell dysfunction associated with symptoms in myalgic encephalomyelitis/ chronic fatigue syndrome (ME/CFS) and Long COVID and treatment with a nebulized antioxidant/antipathogen agent in a retrospective case series. Brain, Behavior, & Immunity – Health (2024), doi: https://doi.org/10.1016/j.bbih.2023.100720 https://www.sciencedirect.com/science/article/pii/S2666354623001345 (Full text)

Role of pharmacological activity of autoantibodies in ME/CFS

Abstract:

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a condition characterised by extreme fatigue, memory impairment, pain and other symptoms that vary from patient to patient. It affects about 0.9% of the population and is often triggered by an acute viral or bacterial infection, such as Epstein-Barr virus. The underlying physiological and molecular basis of ME/CFS is unknown, and no effective treatments exist.

One proposed mechanism is that the blood flow is altered by autoantibodies against receptors involved in blood flow regulation. Antibodies are generated by the immune system to recognise intruders and under normal conditions, our immune system is trained not to attack our own tissues. However, during a severe infection, the immune system adopts an “all hands on deck” approach, which results in some of the newly-produced antibodies escaping quality control and targeting our own tissues, autoantibodies. Receptors regulation blood flow are located in walls of blood vessels and cause a blood vessel to dilate or contract as the demand for oxygen and nutrients to tissues such as the brain or muscles changes. Research has found increased levels of these autoantibodies in ME/CFS patients and initial trials removing these autoantibodies from the blood using a technique called immunoadsorption have shown improvement in symptoms.

In this project, we will test the hypothesis that autoantibodies can activate or inhibit the receptors responsible for the blood flow regulation, in a similar way medical drugs are used to regulate blood pressure.
We aim to profile serum samples from 325 ME/CFS patients and 130 healthy individuals to determine the presence of autoantibodies against all thirty receptors involved in blood pressure regulation. Importantly, we will study the ability of autoantibodies detected in each sample to activate or inhibit these receptors in order to test the hypothesis that the activity of these autoantibodies is a decisive factor in the disease.
If our hypothesis is correct, we will be able to develop an accurate blood test that may be able to detect ME/CFS earlier or to independently confirm the diagnosis. Ultimately, we hope that these results may also indicate a possible route for therapeutic intervention to counteract the effects of autoantibodies and alleviate the ME/CFS symptoms using a combination of already existing drugs, specific for each individual case.

 

Technical Summary:

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a condition of extreme tiredness and brain fog, often triggered by an acute infection. Its prevalence is ca 0.9% and here is no effective treatment. Competing theories for the root cause of ME/CFS include metabolic or redox homeostasis disruption, and presence of autoantibodies (AABs) against G protein coupled receptors (GPCRs) involved in regulation of blood flow.
Triggered by acute infection, autoimmunity is a result of reduced immuno-vigilance during severe infections, when an “all hands on deck” approach confers survival advantage. About 30% of ME/CFS patients show increased titre of autoantibodies against beta2-adrenoceptor and M3/4 muscarinic receptors controlling vasodilation/vasoconstriction, but this could become higher if all 30 receptors controlling blood flow would be taken into account.
In this project, we will test a hypothesis that the pharmacological activity of AABs against GPCRs is the key to their involvement in ME/CFS. Similar to medical drugs, AABs can be stimulatory (agonistic) or inhibitory (antagonistic) and induce a therapeutic or an undesired side effect.
We will profile 325 patient samples and 130 control plasma samples for AABs and their pharmacological activity using a state-of-the art GPCR drug screening pipeline we have established, against all 30 GPCRs involved in blood pressure regulation. We also have machine learning expertise that would allow us to interpret this extensive dataset, extract the most salient features. This will advance the understanding of the molecular basis of ME/CFS and could form the basis of a robust diagnostic blood test for ME/CFS. Ultimately, our findings may point in the direction of developing combination therapy using repurposed drugs to counteract the effects of autoantibodies and mitigate ME/CFS symptoms and stimulate the development of specific B-cell elimination strategy to cure ME/CFS.
Source: Lead Research Organisation: University of Nottingham, Department Name: School of Life Sciences. https://gtr.ukri.org/projects?ref=MR%2FY003667%2F1&pn=0&fetchSize=25&selectedSortableField=date&selectedSortOrder=ASC

Characterization of subgroups of myalgic encephalomyelitis/chronic fatigue syndrome based on disease onset, symptoms and biomarkers

Abstract:

Myalgic encephalomyelitis, also called chronic fatigue syndrome (ME/CFS), is an acquired multisystem disease. The core symptoms include fatigue, exercise intolerance and pain as well as cognitive, autonomic and immunological manifestations. The diagnosis of ME/CFS is based on clinical criteria. Specific biomarkers do not currently exist, but studies suggest a role for soluble cluster of differentiation 26 (sCD26) and autoantibodies (AAK) against G protein-coupled receptors (GPCR). In many cases, the disease begins as a result of infections. 

The aim of this work was to determine the pathophysiological significance of potential biomarkers, assuming different development mechanisms in patients with infection-associated disease onset compared to those with other triggers. In a first study, sCD26, also called dipeptidyl peptidase-4 (DPP-4) due to its enzymatic activity, was analyzed and compared in the serum of 205 ME/CFS patients and 98 controls. This was followed by a comprehensive correlation analysis between sCD26 and clinical and laboratory parameters for ME/CFS patients, separated by type of disease onset. In addition, CD26 expression on lymphocyte subpopulations was determined for 12 patients and 12 controls. 

In another study, a correlation analysis was carried out between AAK against vasoregulatory GPCR and symptoms in 116 ME/CFS patients, separated by type of disease onset. It was shown that in ME/CFS patients with infection-associated disease onset, sCD26 correlated with numerous immunological and metabolic parameters, the changes of which have also been described in connection with DPP-4 inhibitors. In addition, there were inverse correlations with AAK against alpha1-adrenergic and M3-acetylcholine receptors. 

In this subgroup, the second study found correlations between numerous GPCR-AAK and the severity of fatigue, muscle pain and cognitive symptoms as well as greater functional impairment relevant to everyday life. None of these correlations were found in patients without infection-associated disease onset. 

Here, sCD26 correlated inversely with orthostatically induced heart rate increases and AAK against alpha- and beta-adrenergic receptors with the severity of orthostatic symptoms. Different correlation patterns between AAK against GPCR and symptoms allow us to assume that in patients with ME/CFS, an altered function of the AAK or its receptors or signaling pathways has occurred as a result of an infection. The association of sCD26 and GPCR-AAK also indicates the dysregulation of other parts of the immune system with potentially pathological consequences. The differences presented compared to patients with non-infectious genesis suggest two definable subgroups.

Source: Szklarski, Marvin. Characterization of subgroups of myalgic encephalomyelitis/chronic fatigue syndrome based on disease onset, symptoms and biomarkers. Charité – University Medicine Berlin, dissertation. https://refubium.fu-berlin.de/handle/fub188/40276