Tag: etiology

The origin of autoimmune diseases: is there a role for ancestral HLA-II haplotypes in immune hyperactivity

Abstract:

The prevalence of autoimmune diseases in contemporary human populations poses a challenge for both medicine and evolutionary biology. This review explores how the ancestral human leukocyte antigen class II (HLA-II) haplotypes DR2-DQ6, DR4-DQ8 and DR3-DQ2 could play a central role in susceptibility to these diseases.

We propose that these haplotypes, selected in historical contexts of high infectious pressure, may have been maintained because of their ability to elicit strong T-cell responses against pathogens; however, that antigenic promiscuity may be associated with an increased tendency toward immune hyperreactivity in modern environments. This hyperreactivity, involving proinflammatory cytokines including interferon-gamma (IFN-γ), could contribute to the breakdown of tolerance and the emergence of autoimmunity and related clinical phenomena (e.g., Long COVID, myalgic encephalomyelitis/chronic fatigue syndrome and post-vaccination syndromes), although the evidence for the latter remains limited.

Finally, we discuss how chronic infections, immunotherapies, vaccination, obesity and chronic physical stressors may exacerbate this susceptibility and consider the therapeutic implications of integrating HLA-II profiling into clinical practice.

Source: Ruiz-Pablos M, Paiva B, Zabaleta A. The origin of autoimmune diseases: is there a role for ancestral HLA-II haplotypes in immune hyperactivity. Front Immunol. 2025 Dec 4;16:1710571. doi: 10.3389/fimmu.2025.1710571. PMID: 41425584; PMCID: PMC12711860. https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2025.1710571/full (Full text)

Virus-induced endothelial senescence as a cause and driving factor for ME/CFS and long COVID: mediated by a dysfunctional immune system

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long COVID are two post-viral diseases, which share many common symptoms and pathophysiological alterations. Yet a mechanistic explanation of disease induction and maintenance is lacking. This hinders the discovery and implementation of biomarkers and treatment options, and ultimately the establishment of effective clinical resolution. Here, we propose that acute viral infection results in (in)direct endothelial dysfunction and senescence, which at the blood-brain barrier, cerebral arteries, gastrointestinal tract, and skeletal muscle can explain symptoms.

The endothelial senescence-associated secretory phenotype (SASP) is proinflammatory, pro-oxidative, procoagulant, primed for vasoconstriction, and characterized by impaired regulation of tissue repair, but also leads to dysregulated inflammatory processes. Immune abnormalities in ME/CFS and long COVID can account for the persistence of endothelial senescence long past the acute infection by preventing their clearance, thereby providing a mechanism for the chronic nature of ME/CFS and long COVID.

The systemic and tissue-specific effects of endothelial senescence can thus explain the multisystem involvement in and subtypes of ME/CFS and long COVID, including dysregulated blood flow and perfusion deficits. This can occur in all tissues, but especially the brain as evidenced by findings of reduced cerebral blood flow and impaired perfusion of various brain regions, post-exertional malaise (PEM), gastrointestinal disturbances, and fatigue.

Paramount to this theory is the affected endothelium, and the bidirectional sustainment of immune abnormalities and endothelial senescence. The recognition of endothelial cell dysfunction and senescence as a core element in the aetiology of both ME/CFS and Long COVID should aid in the establishment of effective biomarkers and treatment regimens.

Source: Nunes M, Kell L, Slaghekke A, Wüst RC, Fielding BC, Kell DB, Pretorius E. Virus-induced endothelial senescence as a cause and driving factor for ME/CFS and long COVID: mediated by a dysfunctional immune system. Cell Death Dis. 2026 Jan 9;17(1):16. doi: 10.1038/s41419-025-08162-2. PMID: 41513611; PMCID: PMC12789617. https://pmc.ncbi.nlm.nih.gov/articles/PMC12789617/ (Full text)

ME/CFS as a sickness behaviour-like response to HSV-1 infection within the brain: A hypothesis

Highlights:

  • Subset of ME/CFS cases proposed to be caused by a ‘noisy’ latent HSV-1 infection within the brain.
  • HSV-1 proposed to cause local sickness behaviour-like response in the brain.
  • IL-1β, IL-6, TNF-α in the brain proposed to increase sensations of fatigue and pain.

Abstract:

This work presents the hypothesis that a Herpes Simplex Virus 1 (HSV-1) infection in the brain is a significant contributor to the symptoms experienced by a subset of ME/CFS patients. In these patients, an HSV-1 infection has spread from the trigeminal ganglia to the brain, leading to a sickness behaviour-like response that amplifies sensations such as fatigue, pain, and nausea. The hypothesis proposes that ME/CFS is a heterogeneous condition, with a ‘noisy’ latent HSV-1 infection of the brain, and an enduring sickness behaviour-style immune response, an underlying factor for a subset of patients.
Source: John Campbell. ME/CFS as a sickness behaviour-like response to HSV-1 infection within the brain: A hypothesis. Medical Hypotheses, Volume 204, 2025, 111788. ISSN 0306-9877 https://doi.org/10.1016/j.mehy.2025.111788. https://www.sciencedirect.com/science/article/abs/pii/S0306987725002270 (Full text)

HLA and pathogens in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and other post-infection conditions

Abstract:

Viral infections have been widely implicated in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) pathogenesis. Recent evidence has also identified certain Human Leukocyte Antigen (HLA) alleles that are significantly associated with ME/CFS risk/protection. Here we tested the hypothesis that ME/CFS risk or protection conferred from those HLA alleles is associated with binding affinity to antigens of HHV viruses, a critical step in initiating the adaptive immune system response to foreign antigens.

Specifically, we determined in silico the predicted binding affinity of two susceptibility alleles (C*07:04, DQB1*03:03) and two protective alleles (B*08:01, DPB1*02:01) to > 10,000 antigens of the 9 Human Herpes Viruses (HHV1, HHV2, HHV3, HHV4, HHV5, HHV6A, HHV6B, HHV7, HHV8) which have been implicated in the etiology of ME/CFS. We found that the binding affinity of all HHV antigens to the susceptibility alleles was significantly weaker than the binding affinity to the protective alleles (P < 0.001). In fact, none of the HHV antigens showed strong binding to the susceptibility alleles, in contrast to the strong bindings showed by the protective alleles. These findings are in keeping with the hypothesis that the effect of a putative HHV insult in contributing to ME/CFS is modulated by the host’s HLA immunogenetic makeup.

We speculate that strong HLA-antigen binding likely protects against ME/CFS via elimination of virus antigens; conversely, weak HLA-antigen binding may permit persistence of foreign antigens, contributing to ME/CFS and other chronic conditions. Finally, with respect to the latter, we determined the binding affinities to the 4 HLA alleles above to pathogens causing two chronic diseases with very similar symptomatology to ME/CFS, namely Long COVID and post-treatment Lyme disease syndrome (PTLDS).

We found that the 2 ME/CFS susceptibility HLA alleles above had very weak binding with SARS-CoV-2 virus glycoprotein (involved in Long COVID) and 5 proteins of Borrelia burgdorferi (involved in PTLDS), in contrast to the ME/CFS protective alleles that showed strong bindings. These findings support the hypothesis that ME/CFS, long COVID and PTLDS are caused by persistent pathogenic antigens that could not be eliminated due to inadequate protection by the patient’s HLA makeup.

Source: Georgopoulos AP, James LM, Peterson PK. HLA and pathogens in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and other post-infection conditions. Sci Rep. 2025 Oct 24;15(1):37303. doi: 10.1038/s41598-025-21230-z. PMID: 41136524. https://www.nature.com/articles/s41598-025-21230-z (Full text)

Functional and internalizing disorders co-aggregate with cardiometabolic and immune-related diseases within families: a population-based cohort study

Abstract:

Background: Functional disorders share familial risk with internalizing disorders such as generalized anxiety disorder and depression, and are comorbid with cardiometabolic and immune-related diseases. We investigated whether functional and internalizing disorders co-aggregate with these diseases in families to gain insight into the aetiology of functional and internalizing disorders.

Methods: We included 166,774 subjects (aged 3-94), from the population-based Lifelines Cohort Study, a Dutch general population cohort. We defined cases for three functional disorders (myalgic encephalomyelitis/chronic fatigue syndrome; ME/CFS, fibromyalgia, and irritable bowel syndrome; IBS), two internalizing disorders (major depressive disorder; MDD and generalized anxiety disorder; GAD), cardiometabolic diseases (obesity, metabolic associated steatotic liver disease, type 2 diabetes, hypertension and cardiovascular disease) and immune-related diseases (composite measures of auto-immune disease and atopy). We used logistic regression to model the prevalence of these disorders in the general population and in participants with affected relatives. Using these prevalence estimates, we assessed familial co-aggregation with (1) recurrence risk ratios (λR), and (2) familial correlations (rf).

Results: All functional and internalizing disorders co-aggregated with immune-related diseases (λR range 1.06-1.24). ME/CFS, FM, and MDD co-aggregated with most cardiometabolic diseases (λR range 1.00-1.23). MDD, fibromyalgia, and ME/CFS showed similar familial correlation patterns with both disease groups (rf range 0.12-0.44), while patterns of IBS and GAD were more variable.

Conclusions: Internalizing and functional disorders share familial risk with immune-related and cardiometabolic diseases. This suggests that risk factors relevant to immune-related and cardiometabolic diseases may also be relevant for FDs. Future studies should investigate such risk factors to identify novel treatment targets.

Source: Steen OD, Bos M, van Ockenburg SL, Zhou Y, Nolte IM, Snieder H, Kendler K, Rosmalen JGM, van Loo HM. Functional and internalizing disorders co-aggregate with cardiometabolic and immune-related diseases within families: a population-based cohort study. BMC Med. 2025 Aug 11;23(1):469. doi: 10.1186/s12916-025-04293-7. PMID: 40784894. https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-025-04293-7 (Full text)

Neurodevelopment Genes Encoding Olduvai Domains Link Myalgic Encephalomyelitis to Neuropsychiatric Disorders

Abstract:

Background/Objectives: The aetiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), a chronic and severe debilitating disease with a complex phenotype, remains elusive. Associations with infectious diseases and autoimmune and neuropsychiatric disorders have been observed, without the identification of mechanisms. Previous studies suggest that genetic predisposition plays a role, but results are difficult to replicate, with Genome-Wide Association Studies of ME/CFS being challenging due to the relative rareness and heterogeneity of the disorder.
Methods: We studied a well-defined Australian patient cohort diagnosed via the International Consensus Criteria, recruited by a specialist ME/CFS clinic. The whole-exome sequences of 77 patients were contrasted against genome variation in the 1000 Genome Project’s genome-matched population.
Results: Significant associations with ME/CFS were harboured in genes that belong to the Neuroblastoma Breakpoint Family encoding Olduvai (DUF1220) domains, namely NBPF1 (rs3897177, p-value = 3.15 × 10−8), NBPF10 (rs1553120233, p-value = 9.262 × 10−13), and NBPF16 (rs200632836, p-value = 1.04 × 10−6). Other significantly associated variants were detected in the ATR, RSPH10B, ADGRE5-CD97, and NTRK2 genes, among others. Replication of these results was attempted via a GWAS on raw data from a US cohort, which confirmed shared significant associations with variation identified in the PTPRD, CSMD3, RAPGEF5, DCC, ALDH18A1, GALNT16, UNC79, and NCOA3 genes.
Conclusions: These genes are involved in cortical neurogenesis, brain evolution, and neuroblastoma, and have been implicated by several studies in schizophrenia and autism. The sharing of these associations by the two cohorts supports their validity and grants the necessity of future studies to evaluate the implications for ME/CFS aetiology.
Source: Arcos-Burgos, M., Arcos-Holzinger, M., Mastronardi, C., Isaza-Ruget, M. A., Vélez, J. I., Lewis, D. P., Patel, H., & Lidbury, B. A. (2025). Neurodevelopment Genes Encoding Olduvai Domains Link Myalgic Encephalomyelitis to Neuropsychiatric Disorders. Diagnostics, 15(12), 1542. https://doi.org/10.3390/diagnostics15121542 https://www.mdpi.com/2075-4418/15/12/1542 (Full text)

A Mechanical Basis: Brainstem Dysfunction as a Potential Etiology of ME/CFS and Long COVID

Abstract:
The underlying pathologies driving post-acute infectious syndromes (e.g. myalgic encephalomyelitis / chronic fatigue syndrome, long COVID, etc) remain poorly understood. Given the extreme burden these illnesses impose on suffers, and the dramatic increase in cases following the COVID-19 pandemic, it is important to establish a deeper understanding of these pathologies.
We propose a model of how ME/CFS (and related illnesses), might emerge following a viral insult. Central to this hypothesis is the recognition that the core diagnostic features of ME/CFS involve bodily systems known to be governed by the brainstem. This is consistent with the growing literature suggesting that spinal and craniocervical pathologies are over-represented in people with ME/CFS and other post-infectious disorders.
We hypothesize that a non-trivial number of cases of ME/CFS and Long Covid (LC) may have a “mechanical basis.” We propose that an infectious insult may trigger an initial loss of connective tissue integrity in susceptible individuals (e.g. those with pre-existing hypermobility spectrum disorders), which in turn leads to instability at the craniocervical junction, and ultimately mechanical deformation of the brainstem. This ultimately causes widespread autonomic nervous system and immune system dysfunction due to aberrant signaling from the deformed nuclei.
This causal chain may also lead to a vicious cycle: if the dysregulation produced by the initial brainstem deformation leads to a deranged immune response or state of chronic hyper-inflammation, further expression of connective tissue degrading and remodeling factors such as MMPs and mast cells may be triggered. This could further degrade the connective tissues of the craniocervical junction and, in turn, increase mechanical deformation of the brainstem, leading to symptom exacerbation over time and leading to the chronic, lifelong presentation typical of ME/CFS.
Source: Wood, J., Varley, T., Hartman, J., Melia, N., Kaufman, D., & Falor, T. (2025). A Mechanical Basis: Brainstem Dysfunction as a Potential Etiology of ME/CFS and Long COVID. Preprints. https://doi.org/10.20944/preprints202506.0874.v1 https://www.preprints.org/manuscript/202506.0874/v1 (Full text)

Evaluation of viral infection as an etiology of ME/CFS: a systematic review and meta-analysis

Abstract:

Background: Myalgic encephalitis/chronic fatigue syndrome (ME/CFS) is a long-term disabling illness without a medically explained cause. Recently during COVID-19 pandemic, many studies have confirmed the symptoms similar to ME/CFS in the recovered individuals. To investigate the virus-related etiopathogenesis of ME/CFS, we conducted a systematic assessment of viral infection frequency in ME/CFS patients.

Methods: We conducted a comprehensive search of PubMed and the Cochrane Library from their inception through December 31, 2022, using selection criteria of viral infection prevalence in ME/CFS patients and controls. Subsequently, we performed a meta-analysis to assess the extent of viral infections’ contribution to ME/CFS by comparing the odds ratio between ME/CFS patients and controls (healthy and/or diseased).

Results: Finally, 64 studies met our eligibility criteria regarding 18 species of viruses, including a total of 4971 ME/CFS patients and 9221 control subjects. The participants included healthy subjects and individuals with one of 10 diseases, such as multiple sclerosis or fibromyalgia. Two DNA viruses (human herpes virus (HHV)-7 and parvovirus B19, including their co-infection) and 3 RNA viruses (borna disease virus (BDV), enterovirus and coxsackie B virus) showed odds ratios greater than 2.0 compared with healthy and/or diseased subjects. Specifically, BDV exceeded the cutoff with an odds ratio of ≥ 3.47 (indicating a “moderate association” by Cohen’s d test) compared to both healthy and diseased controls.

Conclusion: This study comprehensively evaluated the risk of viral infections associated with ME/CFS, and identified BDV. These results provide valuable reference data for future studies investigating the role of viruses in the causation of ME/CFS.

Source: Hwang, JH., Lee, JS., Oh, HM. et al. Evaluation of viral infection as an etiology of ME/CFS: a systematic review and meta-analysis. J Transl Med 21, 763 (2023). https://doi.org/10.1186/s12967-023-04635-0 https://translational-medicine.biomedcentral.com/articles/10.1186/s12967-023-04635-0 (Full text)

Long read sequencing characterises a novel structural variant, revealing underactive AKR1C1 with overactive AKR1C2 as a possible cause of unexplained severe fatigue

Abstract

Background: Causative genetic variants cannot yet be found for many disorders with a clear heritable component, including chronic fatigue disorders like myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). These conditions may involve genes in difficult-to-align genomic regions that are refractory to short read approaches. Structural variants in these regions can be particularly hard to detect or define with short reads, yet may account for a significant number of cases. Long read sequencing can overcome these difficulties but so far little data is available regarding the specific analytical challenges inherent in such regions, which need to be taken into account to ensure that variants are correctly identified.

Research into chronic fatigue disorders faces the additional challenge that the heterogeneous patient population likely encompasses multiple aetiologies with overlapping symptoms, rather than a single disease entity, such that each individual abnormality may lack statistical significance within a larger sample. Better delineation of patient subgroups is needed to target research and treatment.

Methods: We use nanopore sequencing in a case of unexplained severe fatigue to identify and fully characterise a large inversion in a highly homologous region spanning the AKR1C gene locus, which was indicated but could not be resolved by short-read sequencing. We then use GC-MS/MS serum steroid analysis to investigate the functional consequences.

Results: Several commonly used bioinformatics tools are confounded by the homology but a combined approach including visual inspection allows the variant to be accurately resolved. The DNA inversion appears to increase the expression of AKR1C2 while limiting AKR1C1 activity, resulting in a relative increase of inhibitory neurosteroids and impaired progesterone metabolism.

Conclusions: This study provides an example of how long read sequencing can improve diagnostic yield in research and clinical care, and highlights some of the analytical challenges presented by regions containing tandem arrays of genes. It also proposes a novel gene associated with a specific disease aetiology that may be an underlying cause of complex chronic fatigue and possibly other conditions too. It reveals biomarkers that could be assessed in a larger cohort, potentially identifying a subset of patients who might respond to treatments suggested by the aetiology.

Source: Julia Oakley, Martin Hill, Adam Giess, Mélanie Tanguy, Greg Elgar. Long read sequencing characterises a novel structural variant, revealing underactive AKR1C1 with overactive AKR1C2 as a possible cause of unexplained severe fatigue. ResearchSquare [Preprint] https://www.researchsquare.com/article/rs-3218228/v2 (Full text)

The microbiome in post-acute infection syndrome (PAIS)

Abstract:

Post-Acute Infection Syndrome (PAIS) is a relatively new medical terminology that represents prolonged sequelae symptoms after acute infection by numerous pathogenic agents. Imposing a substantial public health burden worldwide, PASC (post-acute sequelae of COVID-19 infection) and ME/CFS (myalgic encephalomyelitis/chronic fatigue syndrome) are two of the most recognized and prevalent PAIS conditions. The presences of prior infections and similar symptom profiles in PAIS reflect a plausible common etiopathogenesis. The human microbiome is known to play an essential role in health and disease.

In this review, we reviewed and summarized available research on oral and gut microbiota alterations in patients with different infections or PAIS conditions. We discussed key theories about the associations between microbiome dysbiosis and PAIS disease development, aiming to explore the mechanistic roles and potential functions the microbiome may have in the process. Additionally, we discuss the areas of knowledge gaps and propose the potential clinical applications of the microbiome for prevention and treatment of PAIS conditions.

Source: Guo C, Yi B, Wu J, Lu J. The microbiome in post-acute infection syndrome (PAIS). Comput Struct Biotechnol J. 2023 Aug 5;21:3904-3911. doi: 10.1016/j.csbj.2023.08.002. PMID: 37602232; PMCID: PMC10432703. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10432703/ (Full text)