**Background:** Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating illness characterized by persistent fatigue and a constellation of symptoms including rhinitis, dry eyes, and sore throat. Approximately 75–80% of ME/CFS subjects have irritant rhinitis with increased mucin production, and sicca symptoms occur in about 70% of patients. Non-exudative pharyngitis is reported in up to 80% of patients. The etiology of ME/CFS remains unclear, but genetic studies have identified abnormal variants in mucin genes (MUC16, MUC19, MUC22) in 70–80% of ME/CFS subjects at 1.60 to 3.75 times the reference population. Mucin proteins form protective mucosal barriers in the eyes, respiratory tract, and otolaryngological pathways. This paper hypothesizes that dysfunctional mucin proteins compromise these barriers, leading to chronic low-grade inflammation and symptom exacerbation in ME/CFS.
**Methods:** The authors present a hypothesis based on genetic analysis and computational modeling. They cite a pilot genome-wide SNP study of 383 ME/CFS subjects (Perez et al. 2019) showing variants in MUC16, MUC19, and MUC22. For example, MUC19 SNP rs10784618 (stop-gained, CADD score 36) is predicted to be among the 0.03% most deleterious substitutions, causing a severely truncated mucin-19 protein. MUC19 SNP rs11564109 (missense C>Y, CADD 24.7) affects disulfide bond formation. MUC16 and MUC22 variants result in amino acid changes in extracellular domains. To provide a theoretical framework, the authors constructed a discrete ternary logic model of the ocular and otolaryngological mucosal-innate immune signaling system based on literature (Repentigny et al. 2015; Ohradanova-Repic et al. 2023; and others). The model includes nodes for immune cells, cytokines, and environmental pathogens, with three discrete states (−1 suppressed, 0 normal, +1 increased). The system was updated asynchronously to identify steady states. The model predicted three stable states: SS0 (healthy), SS1 (increased Th1 pro-inflammatory profile), and SS2 (mixed inflammatory state with increased Th1 and decreased Th2/Th17/Treg). To test applicability to ME/CFS, the authors compared model predictions to plasma cytokine data from 65 female subjects (29 ME/CFS, 36 healthy controls) and 53 male subjects (25 ME/CFS, 28 healthy controls) from the Institute for Neuroimmune Medicine at Nova Southeastern University. Cytokines (IL1β, IL2, IL4, IL6, IL8, IL10, IL12p70, IL13, IL17, IL23, IFNγ, TNFα) were measured via Q-Plex multiplex ELISA. A meta-analysis using Brown's theoretical approximation of Fisher's statistics was used to calculate the significance of similarity between cytokine profiles and model-predicted steady states. Multidimensional scaling projected the comparisons into 2D space.
**Key Results:** The logic model identified three stable states: SS0 (healthy), SS1 (inflammatory with increased pro-inflammatory cytokines and Th1 shift), and SS2 (mixed inflammatory with increased Th1 and decreased Th2/Th17/Treg). For female ME/CFS subjects, the cytokine profile was most closely aligned with SS1 (inflammatory state), characterized by increased IL1β, IL2, IL6, IL12, IL17, IL23, IFNγ, TNFα, and activation of innate immune cells. The next nearest state was SS2. Female ME/CFS profiles were furthest from the healthy state SS0. For male ME/CFS subjects, the cytokine profile was near equidistant from SS0 and SS1, with SS1 slightly more favorable, but closest to SS2 (mixed inflammatory state). No significant differences were found in male cytokine comparisons (p<0.05 for two-tailed heteroscedastic t-test in females; no significant differences in males). The authors note that the model predicts that pathogen influx with deficient mucus protection can force the system into these alternate stable states, perpetuating chronic low-grade inflammation.
**Clinical Implications:** The hypothesis suggests that genetic variants in mucin proteins (MUC16, MUC19, MUC22) may cause a compromised mucosal barrier in the eyes, nose, throat, and airways, leading to increased epithelial irritation and chronic low-grade inflammation. This aligns with the high prevalence of rhinitis, dry eyes, and sore throat in ME/CFS. The computational model indicates that once the immune system enters an alternate stable state (SS1 or SS2), it becomes self-perpetuating and resistant to change, potentially explaining the chronic nature of ME/CFS. The sex differences observed (females aligning more with SS1, males with SS2) are consistent with known sex differences in ME/CFS symptomatology and immune measures. The hypothesis also links mucin dysfunction to other ME/CFS features: chemical sensitivities (due to a sensitive epithelium), increased susceptibility to infections (e.g., EBV, HHV-6, SARS-CoV-2), and reduced NK cell function (mucin-16 can inhibit NK cell cytotoxicity). The authors note that MUC16 SNPs are associated with lower T-cell responses and changes in brain grey matter volumes, while MUC19 SNPs are linked to asthma and acute lymphocytic leukemia, and MUC22 SNPs to ankylosing spondylitis and multiple sclerosis. Future work is needed to directly investigate the functional consequences of these mucin variants and the role of the ocular and otolaryngological mucus layer in ME/CFS.