A Shared Biology of Chronic Fatigue May Span Five Diseases

Chronic fatigue is one of medicine's most stubborn mysteries: a bone-deep exhaustion that sleep cannot fix, arriving after viral infections, psychological trauma, and autoimmune flare-ups alike. Now a team of researchers in the United Kingdom says that the shared misery may have a shared mechanism, as reported by Medical Xpress.

The analysis, published in September 2026 in the Journal of Translational Medicine, was led by Professor Dmitry Pshezhetskiy at the University of East Anglia's Norwich Medical School together with Oxford BioDynamics. It looked across five conditions long treated as unrelated: myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), long Covid, post-traumatic stress disorder, rheumatoid arthritis, and multiple sclerosis. The goal was to explain why chronic fatigue looks so similar across such different diagnoses.

A shared pattern of chronic fatigue across five illnesses

At the level of individual genes, the five illnesses barely resembled each other, according to a summary from Labcompare. But when the team analyzed how those genes interact inside larger biological networks, a different picture emerged: genes tied to each illness fed into the same core systems, including immune and inflammatory signaling, mitochondrial energy production, metabolic regulation, stress-response pathways, and communication between the brain and hormone systems. "This is not something you can see by reading the genetic sequence alone," Pshezhetskiy said.

The symptom overlap is what made the comparison worth attempting. The condition often follows a viral infection, long Covid develops after SARS-CoV-2, PTSD emerges from traumatic experiences, rheumatoid arthritis attacks the joints, and multiple sclerosis attacks the nervous system, according to the UEA announcement. Yet patients across all five groups report strikingly similar symptoms: overwhelming fatigue, brain fog, poor concentration, disturbed sleep, and a dramatic reduction in everyday functioning. Pshezhetskiy described the finding as "something approaching a biological unifying theory of fatigue."

The finding marks a sharp break from how chronic fatigue has historically been studied. For decades, each condition was investigated in isolation, and patients with the syndrome in particular have spent years cycling between doctors, partly because no lab test can confirm the diagnosis. Earlier work using the same EpiSwitch technology had already produced a blood-based test for the condition with high diagnostic accuracy, though it still needs clinical validation, according to reporting from Bright Surf. The new study extends that approach across disease borders, using Oxford BioDynamics' EpiSwitch Orion platform to read the three-dimensional architecture of the genome — how DNA folds inside the nucleus — instead of just the sequence of genes.

The method also sets this work apart from earlier single-disease studies, which tended to hunt for one gene or one pathway at a time. Here, the researchers combined existing genome-wide association data on long Covid, PTSD, rheumatoid arthritis, and multiple sclerosis with three-dimensional genomic data from an earlier chronic fatigue syndrome study, without collecting any new patient samples. The result is less a single "fatigue gene" and more a fatigue map: a framework showing how very different triggers can disturb the same regulatory networks that govern energy and stress.

What T-cell exhaustion actually means

One of the most concrete leads involves LAG3, a gene flagged as a "hub" sitting at a busy intersection of the shared networks. It is linked to T-cell exhaustion, a state in which immune T cells become worn out and less effective after prolonged activation. Picture a security team that stays on high alert for so long it can no longer respond properly to real threats — that is essentially what happens to immune cells that never get to stand down, and one plausible reason chronic fatigue persists long after the original trigger is gone.

That lead matters because it could eventually support real diagnostic tools. ME/CFS and long Covid currently lack a universally accepted laboratory test, a major reason so many patients go undiagnosed, as reported by Knowridge. The research team hopes the shared pathways could eventually guide blood markers that identify biological signatures instead of relying only on symptoms patients report. Pshezhetskiy said the work could eventually support objective blood tests.

What the chronic fatigue study does not prove yet

The scale of the problem makes that prospect tantalizing. The U.S. Centers for Disease Control and Prevention estimates that up to 3.3 million people in the United States live with the condition, and more than nine in ten of them have never received a diagnosis, according to the CDC. Global estimates put the worldwide figure at 17 to 24 million people, according to a peer-reviewed review citing CDC figures, while long Covid is estimated to have affected more than 400 million people as of 2024, as reported by The Sick Times.

Still, caution is warranted. The study was a computational analysis of existing data, not a laboratory experiment, and it does not prove that all five illnesses share a single cause or that the shared pathways directly cause fatigue, as reported by Knowridge. Laboratory studies and research involving more patients will be needed to confirm the proposed connections. For now, the work is best understood as its authors describe it: a framework for studying chronic fatigue across diseases that were traditionally investigated separately — and a new starting point for research that has lagged for decades.

For young people living with unexplained exhaustion, the shift from dismissed symptom to shared biology could change how doctors approach these conditions. Until blood markers arrive, the nearer-term answers sit in sleep and energy science — explored in more Health coverage, including a deep dive into the 95,000-person sleep study linking REM sleep to dozens of diseases.