Pathophysiology: Metabolic and Mitochondrial Dysfunction
1 Mitochondrial Dysfunction
Full Citation:: Holden S, Maksoud R, Eaton-Fitch N, et al. Mitochondrial Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Physiology. 2025;40(2):89–102. DOI:: 10.1152/physiol.00056.2024 PMCID:: PMC12151296 Key Topics:: Impaired oxidative phosphorylation, reduced ATP production, WASF3 dysregulation.
Wang et al. 2023 — WASF3 Disrupts Mitochondrial Respiration
Key Findings: This PNAS study identifies a specific molecular mechanism for mitochondrial dysfunction in ME/CFS. ER stress-induced WASF3 protein disrupts respiratory supercomplex assembly in mitochondria, leading to impaired oxygen consumption and exercise intolerance. Muscle biopsies from 14 ME/CFS patients showed elevated WASF3 and aberrant ER stress activation compared to 10 healthy controls. Critically, shRNA knockdown of WASF3 in patient cells restored respiratory capacity to normal levels, providing proof-of-principle for reversibility. Transgenic mice with elevated WASF3 recapitulated the human phenotype: reduced treadmill running capacity, elevated blood lactate at rest, and impaired respiratory supercomplex assembly.
Relevance: Establishes a mechanistic link from viral triggers (ER stress) through WASF3 to mitochondrial dysfunction and exercise intolerance. Provides molecular explanation for 2-day CPET findings (Keller 2024, Lim 2020) and ATP depletion observed in other studies (Heng 2025). Identifies WASF3 as a specific therapeutic target, though no inhibitors are currently available for human use.
Certainty Assessment:
- Quality: High (published in PNAS, rigorous methodology, multi-level validation)
- Sample: n=14 ME/CFS patients, n=10 controls (small but adequate for mechanistic study)
- Replication: Pending (published 2023, too recent for independent validation)
- Limitations: Unknown whether WASF3 elevation applies to all ME/CFS patients or specific subgroup; therapeutic compounds not yet developed
Full Citation:: Morris G, Maes M. Mitochondrial dysfunctions in myalgic encephalomyelitis/chronic fatigue syndrome explained by activated immuno-inflammatory, oxidative and nitrosative stress pathways. Metabolic Brain Disease. 2014;29(1):19–36. DOI:: 10.1007/s11011-013-9435-x PMID:: 24557875
Full Citation:: Myhill S, Booth NE, McLaren-Howard J. Chronic fatigue syndrome and mitochondrial dysfunction. International Journal of Clinical and Experimental Medicine. 2009;2(1):1–16. PMCID:: PMC2680051
Yamano et al. 2016 — TCA and Urea Cycle Dysfunction
Key Findings: Metabolomic study using capillary electrophoresis time-of-flight mass spectrometry identified significant dysfunction in both the tricarboxylic acid (TCA/Krebs) cycle and urea cycle in ME/CFS patients. Plasma concentrations of TCA cycle intermediates (citrate, isocitrate, malate) were significantly lower in patients than controls, indicating impaired energy production. Urea cycle showed decreased citrulline and elevated ornithine, suggesting a metabolic bottleneck in ammonia detoxification. The researchers developed a diagnostic model using two metabolite ratios: pyruvate/isocitrate and ornithine/citrulline, achieving discrimination accuracy suitable for clinical screening.
Relevance: Provides mechanistic basis for L-citrulline-malate supplementation in ME/CFS, as this combination directly addresses both documented deficiencies. The citrulline deficiency impairs both the urea cycle (ammonia clearance) and serves as a precursor for nitric oxide synthesis. The malate deficiency disrupts TCA cycle flux and mitochondrial ATP production. Together, these findings explain energy production impairment and may contribute to cognitive symptoms through impaired ammonia detoxification. Offers objective biomarkers (metabolite ratios) for diagnosis and treatment monitoring.
Certainty Assessment:
- Quality: High (rigorous metabolomic methodology, published in Nature Scientific Reports, peer-reviewed)
- Sample: Not specified in available abstract (typical metabolomic studies: n=30–50 per group)
- Replication: Consistent with other metabolomic studies showing TCA dysfunction; citrulline findings replicated
- Limitations: Cross-sectional design cannot establish causality; no intervention component; primary vs secondary dysfunction unclear
Shungu et al. 2012 — Cortical Glutathione Deficiency and Oxidative Stress
Key Findings: First magnetic resonance spectroscopy (MRS) documentation of significantly reduced cortical glutathione (GSH) in ME/CFS brain tissue compared to healthy controls. The study also replicated elevated ventricular lactate, indicating cellular energetic stress. Critically, GSH and lactate showed a strong negative correlation (r = -0.545, p = 0.001), suggesting linked mechanisms of oxidative stress and energy impairment. GSH levels correlated positively with physical functioning (\(\rho\) = 0.506, p = 0.001) and energy levels (\(\rho\) = 0.606, p < 0.001), while lactate correlated with fatigue severity (\(\rho\) = 0.581, p < 0.001). Pilot data from this research group showed that N-acetylcysteine (NAC) supplementation (1800 mg/day for 4 weeks) normalized brain GSH and lactate levels while improving symptoms.
Relevance: Establishes oxidative stress as a central, quantifiable pathophysiological mechanism in ME/CFS with direct clinical correlates. Provides strong rationale for NAC supplementation over direct glutathione supplementation, as NAC crosses the blood-brain barrier and stimulates in situ GSH synthesis where needed. The correlation between GSH deficiency and disability severity suggests that restoring antioxidant capacity may improve functional outcomes. A 2020 NINDS clinical trial (NCT04542161) is testing optimal NAC dosing (900 mg vs 3600 mg daily) for ME/CFS.
Certainty Assessment:
- Quality: High (rigorous MRS neuroimaging methodology, strong statistical correlations, peer-reviewed in NMR in Biomedicine)
- Sample: Size not specified in abstract; typical MRS studies: n=20–30 per group
- Replication: Confirmed by subsequent 7 Tesla MRI study (2021) showing reduced glutathione, creatine, myo-inositol
- NAC Evidence: Pilot data (medium certainty); formal RCT underway (NINDS 2020)
- Limitations: Cross-sectional design for correlational data; pilot NAC study small; awaiting RCT results for definitive dosing
Ogawa et al. 1998 — Impaired L-Arginine–Nitric Oxide–NK Cell Pathway
Key Findings: In vitro case-control study (n=20 CFS, n=21 controls) demonstrated that L-arginine treatment (24 hours) significantly enhanced natural killer cell activity in healthy controls but completely failed to produce any effect in CFS patients. Even direct nitric oxide (NO) donor compounds, which bypass the L-arginine conversion step, did not activate NK cells in patients. Critically, inducible NO synthase (iNOS) gene expression was normal in both groups, indicating that the dysfunction is not at the transcriptional level but rather in the functional pathway from L-arginine \(\to\) NO \(\to\) NK activation.
Relevance: Critical negative finding: Demonstrates that L-arginine supplementation alone is insufficient for restoring immune function in ME/CFS. The pathway dysfunction suggests that simply providing substrate (L-arginine) cannot overcome downstream impairments. This implies that successful intervention requires either: (1) L-citrulline (superior bioavailability, bypasses hepatic metabolism), (2) essential cofactors for NOS enzymes (e.g., tetrahydrobiopterin/BH4), or (3) combination therapy addressing multiple steps in NO synthesis. Explains why comprehensive metabolic support protocols (Myhill 2012) succeed where single amino acid interventions fail. Important caveat for interpreting patient reports of amino acid benefits—success likely reflects combination approaches, not isolated arginine supplementation.
Certainty Assessment:
- Quality: Medium (well-designed in vitro study, clear methodology, published in European Journal of Clinical Investigation)
- Sample: n=20 CFS (small but adequate for proof-of-concept)
- Replication: Findings consistent with later endothelial dysfunction research; supported by BH4 metabolism studies (2025)
- Limitations: In vitro (may not reflect in vivo conditions); no in vivo supplementation trial; mechanism of downstream dysfunction not fully elucidated; study from 1998 predates much current ME/CFS research
Myhill et al. 2012 — Clinical Audit of Comprehensive Mitochondrial Support
(Myhill, Booth, and McLaren-Howard 2012)
Key Findings: Clinical audit of comprehensive mitochondrial support protocol in 138 ME/CFS patients, with 34 (25%) receiving follow-up ATP profile testing. All 30 patients with good protocol adherence showed improvements in mitochondrial function: average increase of 4.14-fold in Mitochondrial Energy Score (MESinh), 100% improved in oxidative phosphorylation efficiency, and 93% (28/30) improved in ATP availability. Cell-free DNA (tissue damage marker) decreased in compliant patients. Four patients with poor adherence showed minimal improvement or deterioration, demonstrating the requirement for sustained commitment. The protocol included four foundational components: (1) stone-age diet (low-carb, high-fat, whole foods), (2) sleep optimization, (3) comprehensive nutritional supplementation (L-carnitine, glutathione, CoQ10, niacinamide, B12, D-ribose, magnesium), and (4) pacing (appropriate work-rest balance).
Relevance: Provides clinical validation that mitochondrial dysfunction in ME/CFS is amenable to treatment through comprehensive metabolic support. The 4-fold improvement in objective biomarkers (ATP profile) is clinically significant and suggests that addressing multiple metabolic deficiencies simultaneously is necessary for optimal outcomes. Critical insight: The non-compliant patient data (internal control group) demonstrates that partial adherence is insufficient—all four components appear necessary. However, the audit does not establish which specific supplements are essential versus adjunctive. The lack of specific dosages is a major limitation for clinical replication.
Certainty Assessment:
- Quality: Medium (prospective clinical audit with objective biomarkers, but not RCT—no randomization, placebo, or blinding)
- Sample: n=30 compliant patients with follow-up testing (moderate sample size; 75% of initial cohort lacked follow-up)
- Effect Size: Large (4-fold improvement in MESinh)
- Replication: Same research group as Myhill 2009; needs independent replication
- Limitations: Not RCT; specific dosages not provided; treatment duration not specified; no component analysis (factorial design); selection bias (compliant patients may be more motivated); internal validity concerns
Conflict of Interest Disclosure:
The lead author (Dr. Sarah Myhill) operates a clinical practice specializing in ME/CFS treatment and sells nutritional supplements mentioned in the protocol through associated businesses. While this does not invalidate the findings, it creates potential for:
- Publication bias: Increased likelihood of publishing positive results while negative or null findings remain unreported
- Optimistic interpretation: Financial incentive may unconsciously influence interpretation of ambiguous data
- Selection bias: Patients willing to pay for comprehensive supplement protocols may differ systematically from general ME/CFS population
- Replication challenges: Independent researchers without financial stake are essential for validation
The objective biomarker data (ATP profiles) provides some protection against subjective bias, but the lack of blinding and placebo control means that both patient expectations and investigator interpretation could influence results. Independent replication by researchers without financial conflicts is critically needed before these findings can be considered established.
2 Methylation Cycle and Homocysteine in ME/CFS
Key Findings: Comprehensive review documenting that hyperhomocysteinemia (HHcy) inhibits mitochondrial electron transport chain complexes I through V in cardiac and neural tissue, generates reactive oxygen species through dual routes (homocysteine auto-oxidation and ETC impairment), depletes antioxidant defenses (mitochondrial SOD, catalase), and disrupts mitochondrial dynamics via DRP1/Mfn2/Opa1 imbalance. Brain-specific complex I inhibition is persistent. N-homocysteinylation of cytochrome c directly disrupts electron transport.
Relevance: Provides biochemical mechanism linking elevated homocysteine to the mitochondrial dysfunction documented in ME/CFS. The ETC complex inhibition and ROS generation pathways overlap with independently documented ME/CFS mitochondrial abnormalities. NOTE: this review covers cardiovascular and neurological models; direct ME/CFS patient data are absent.
Certainty Assessment:
Quality: Medium (comprehensive narrative review of multiple independent studies)
Sample: N/A (review of animal and in vitro models)
Replication: Individual mechanisms replicated across independent groups in cardiovascular/neurological literature
Limitations: No ME/CFS patient data; predominantly animal and in vitro; dose-response quantification inconsistent across studies
Key Findings: All 12 female FM/CFS patients showed elevated cerebrospinal fluid (CSF) homocysteine; serum homocysteine was not elevated. Significant positive correlation between CSF homocysteine and fatiguability (CPRS). CSF vitamin B12 was generally low; CSF B12 correlated with mental fatigue severity. Authors conclude that CNS-localized B12 deficiency impairs homocysteine remethylation.
Relevance: Foundational study establishing a CNS-compartment-specific homocysteine elevation in CFS, and directly correlating it with fatigue severity. Motivates the hypothesis that standard serum homocysteine testing may miss CNS-localized methylation failure in ME/CFS patients.
Certainty Assessment:
Quality: Low-Medium (clinical biochemical study with psychopathological rating)
Sample: n=12 (very small)
Replication: Not independently replicated; same group provided supportive but not independent follow-up
Limitations: Very small sample; combined FM+CFS cohort; all female; no matched healthy control group; pre-ICC/CCC diagnostic criteria; single academic group
Key Findings: Cross-sectional survey of 38 ME/FM patients receiving B12 injections. Good responders (n=15, Fibro Fatigue score \(\leq\) 24) used more frequent injections, higher doses, longer duration, and higher folic acid doses matched to MTHFR genotype compared to mild responders (n=23). Methylcobalamin appeared more effective than hydroxycobalamin. Dose-response relationship observed. Daily analgesic use was a strong negative predictor of good response.
Relevance: Provides clinical evidence that MTHFR-guided B12/folate supplementation at therapeutic doses may improve ME/FM outcomes. Establishes that methylcobalamin form and MTHFR genotyping may be clinically relevant. Cannot establish causality given observational design.
Certainty Assessment:
- Quality: Low-Medium (cross-sectional observational study, no placebo control)
- Sample: n=38
- Replication: Not independently replicated by separate group; RCT absent
- Limitations: Combined ME+FM cohort; open-label design; same research group as Regland 1997; potential confounding by analgesic use and disease severity
Campen, Riepma, and Visser (2019)
Key Findings: Open trial of intranasal hydroxocobalamin (B12) in 51 ME/CFS adults over 3 months. Serum B12 rose from median 328 to 973 pmol/L. In 34/51 responders (67%), step count (actigraphy), RAND-36 physical activity, and B12 levels all increased significantly. Non-responders (33%) showed no change. Authors call for placebo-controlled RCT.
Relevance: Supports biological plausibility of B12 supplementation in ME/CFS via an objective functional outcome (step count). Intranasal route achieves CNS-accessible delivery relevant to the Regland 1997 hypothesis of CNS B12 deficiency. The 33% non-responder rate suggests patient stratification is needed.
Certainty Assessment:
- Quality: Low-Medium (open-label pilot trial, no placebo control)
- Sample: n=51
- Replication: Not replicated; pilot study only
- Limitations: No blinding; single center; potential placebo effect; seasonal confound for step count over 3 months
(Zarembska, Ślusarczyk, and Wrzosek 2023)
Key Findings: Review documents that MTHFR C677T polymorphism reduces enzyme activity to 67% (heterozygotes) and 25% (TT homozygotes). Reduced activity impairs 5-methyltetrahydrofolate production, directly impairing homocysteine remethylation. Elevated homocysteine from MTHFR dysfunction increases oxidative stress. One-carbon metabolism disruptions affect both nuclear and mitochondrial DNA methylation.
Relevance: Provides mechanistic foundation for why a substantial fraction of ME/CFS patients may be predisposed to homocysteine elevation via MTHFR polymorphisms, even with adequate dietary folate. The mitochondrial DNA methylation implications provide a direct mechanistic bridge from MTHFR deficiency to OXPHOS gene expression alteration.
Certainty Assessment:
Quality: Medium-High (comprehensive narrative review of replicated biochemistry)
Sample: N/A (review)
Replication: MTHFR-HHcy association is among the most replicated findings in human genetics
Limitations: Not ME/CFS-specific; MTHFR prevalence in ME/CFS relative to general population not established; narrative review subject to selection bias
Key Findings: Hypothesis paper proposing that SARS-CoV-2 simultaneously depletes methyl groups (by consuming them for viral RNA modification via m6A and capping) and impairs their resupply (by oxidative inactivation of methionine synthase). Authors predict this elevates homocysteine and depletes SAM. Long-COVID fatigue (87%) and memory complaints (78%) overlap with pernicious anemia at similar rates, suggesting a shared methylation-deficiency phenomenology. Cites Regland 1997 to connect ME/CFS to the same pathway.
Relevance: Provides a mechanistic hypothesis for how viral triggers (including those causing post-viral fatigue/ME/CFS) could initiate methylation cycle depletion. Relevant to post-viral ME/CFS onset pathophysiology. Requires empirical confirmation.
Certainty Assessment:
- Quality: Low (hypothesis paper; Medical Hypotheses journal; no primary data)
- Sample: N/A
- Replication: Mechanism unconfirmed; testable predictions not yet validated
- Limitations: Speculative by design; Medical Hypotheses does not apply standard empirical peer review; requires in vivo confirmation
Key Findings: Case report of an adolescent with comorbid ME/CFS, postural tachycardia syndrome (POTS), and narcolepsy found to carry compound heterozygous MTHFR mutations with markedly elevated serum homocysteine (86 \(\mu\)mol/L). Symptoms improved with targeted methylation support. Documents extreme end of the MTHFR–homocysteine–ME/CFS spectrum.
Relevance: While a single case report cannot establish causation, the co-occurrence of MTHFR mutations, severe hyperhomocysteinemia, and ME/CFS+POTS+narcolepsy in one patient illustrates the potential clinical significance of the methylation pathway in predisposed individuals.
Certainty Assessment:
- Quality: Very Low (single case report)
- Sample: n=1
- Replication: Not applicable (case report)
- Limitations: Single patient; compound heterozygous genotype is rare; improvement could reflect natural course or other interventions
Key Findings: Systematic review of 101 ME/CFS biomarker studies. Identified immunological, metabolomic, and autonomic biomarker candidates. Homocysteine was not identified among validated biomarker candidates, reflecting the absence of large-scale validation studies rather than confirmed negative findings.
Relevance: Provides context for the CSF homocysteine findings of Regland et al. (Regland et al. 1997): homocysteine has not been systematically evaluated as a biomarker in ME/CFS despite the suggestive small-sample CSF data. The absence from this systematic review highlights a research gap rather than refuting the biomarker hypothesis.
Certainty Assessment:
- Quality: High (systematic review with comprehensive search strategy)
- Sample: 101 studies reviewed
- Replication: N/A (systematic review)
- Limitations: Heterogeneous study quality across reviewed papers; publication bias possible; homocysteine absence may reflect search terms rather than deliberate exclusion
3 Metabolomics and Metabolic Traps
Phair et al. 2019 — The IDO Metabolic Trap Hypothesis
(Phair, Davis, and Kashi 2019)
Key Findings: Mathematical model proposing bistability in tryptophan metabolism as an etiological mechanism for ME/CFS. The model combines IDO2 loss-of-function mutations (observed in all patients in the Severely Ill Big Data Study) with well-established IDO1 substrate inhibition and LAT1 transporter asymmetry. The system exhibits two stable steady-states: physiological (normal tryptophan/kynurenine) and pathological (elevated tryptophan, reduced kynurenine due to IDO1 inhibition). A critical cytosolic tryptophan threshold determines irreversible transition to the trapped state. Hysteresis effect explains chronicity: different thresholds for entering versus escaping the trap.
Relevance: Provides theoretical framework for understanding chronic ME/CFS and suggests testable therapeutic interventions (reducing cytosolic tryptophan below critical threshold). However, the model’s predictions show mixed empirical support: IDO2 mutations have not been replicated in other cohorts, and metabolomics studies show variable tryptophan/kynurenine patterns. Critical contradiction: Guo et al. 2023 found opposite mechanism in long COVID (IDO2 gain-of-function with low tryptophan, high kynurenine), suggesting different mechanisms may operate in different patient subgroups or diseases.
Certainty Assessment:
- Quality: High (rigorous mathematical modeling)
- Empirical Support: Low-Moderate (genetic findings not replicated; metabolomics inconsistent)
- Validation: Pending (therapeutic predictions untested; contradicted by Guo 2023)
- Limitations: Theoretical model with limited validation; IDO2 mutation ubiquity not confirmed in independent cohorts; use as speculative hypothesis for subset of patients
Full Citation:: Baraniuk JN, Kern G, Engel S, Engel G. Cerebrospinal fluid metabolomics, lipidomics and serine pathway dysfunction in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Scientific Reports. 2025;15(1):6789. DOI:: 10.1038/s41598-025-91324-1 PMCID:: PMC11873053 Key Findings:: Elevated serine, reduced 5-MTHF in CSF; altered phospholipid synthesis.
Full Citation:: Naviaux RK, Naviaux JC, Li K, et al. Metabolic features of chronic fatigue syndrome. Proceedings of the National Academy of Sciences. 2016;113(37):E5472–E5480. DOI:: 10.1073/pnas.1607571113 Key Findings:: Chemical signature with approximately 40 metabolic abnormalities; hypometabolic state.
Full Citation:: Germain A, Barupal DK, Levine SM. Comprehensive Circulatory Metabolomics in ME/CFS Reveals Disrupted Metabolism of Acyl Lipids and Steroids. Metabolites. 2020;10(1):34. DOI:: 10.3390/metabo10010034 PMID:: 31947545 Key Findings:: Acyl cholines consistently reduced across cohorts.