Myasthenia gravis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Fahimeh Shojaei, M.D., Keanu Ngo[2]
Overview
Myasthenia gravis (MG) is an antibody-mediated autoimmune disorder of the postsynaptic neuromuscular junction (NMJ) in which pathogenic IgG autoantibodies reduce the number or function of postsynaptic proteins, lowering the safety factor for neuromuscular transmission and producing fluctuating, fatigable weakness. The principal antigenic targets are the nicotinic acetylcholine receptor (AChR, ~80–85%), muscle-specific kinase (MuSK, ~5–8%), and lipoprotein receptor-related protein 4 (LRP4, ~1–5%). AChR antibodies (complement-fixing IgG1/IgG3) act through complement-mediated membrane destruction, antigenic modulation, and functional blockade, whereas MuSK antibodies (predominantly non-complement-fixing IgG4) block the LRP4–MuSK interaction and disperse AChR clusters. Loss of immune self-tolerance—centered on the thymus in early-onset AChR-MG—drives autoantibody production, and susceptibility is strongly influenced by subtype-specific HLA and non-HLA immunogenetic loci.
Pathophysiology
Normal Neuromuscular Transmission
- A nerve action potential opens presynaptic voltage-gated calcium channels, triggering vesicular release of acetylcholine (ACh) into the synaptic cleft.[1]
- ACh binds the postsynaptic AChR—a pentamer of two α1, one β1, one δ, and one ε (adult) or γ (fetal) subunit—generating an endplate potential that, when above threshold, triggers a muscle action potential; acetylcholinesterase terminates the signal.[1][2]
- Postsynaptic AChR density is maintained by the agrin–LRP4–MuSK–Dok7 clustering pathway: nerve-derived agrin binds LRP4, which complexes with and dimerizes MuSK; activated MuSK recruits Dok7 and rapsyn to cluster AChRs opposite ACh release sites. Normal transmission carries a large "safety factor," and MG pathology reduces this margin so that weakness worsens with repetitive activity.[3][4]
AChR Antibody-Positive MG
AChR antibodies are predominantly complement-fixing IgG1/IgG3 directed at the extracellular α1 main immunogenic region and reduce AChR number and function by three mechanisms:[1][5]
- Complement activation (dominant effector): Bound antibody fixes C1q, driving the classical cascade to membrane attack complex (MAC) formation, which destroys the postsynaptic membrane, causes loss of AChRs and simplification of junctional folds (widening the cleft), and reduces voltage-gated sodium channels—raising the firing threshold. Complement-deficient (C3/C4/C5/C6) animals resist experimental autoimmune MG, and human NMJs show IgG, C3, and C9 deposits with complement consumption during exacerbations.[2][6]
- Antigenic modulation: Divalent antibody cross-links AChRs, accelerating internalization and lysosomal degradation faster than resynthesis.[5][7]
- Functional blockade: Some antibodies sterically block the ACh binding site.[5][8]
Individual monoclonal AChR autoantibody clones can execute more than one of these mechanisms simultaneously, so complement, modulation, and blockade are not mediated by separate antibody populations.[9]
MuSK Antibody-Positive MG
- MuSK antibodies are predominantly IgG4, which cannot fix complement and bind Fc receptors weakly. Pathogenic IgG4 becomes functionally monovalent through Fab-arm exchange and blocks the LRP4–MuSK interaction, abolishing MuSK activation, dispersing existing AChR clusters, and causing synaptic disintegration—without complement-mediated destruction.[10][11]
- IgG1–3 MuSK antibodies can also disperse preformed (Dok7-driven) AChR clusters and contribute to pathology.[12]
- Because MuSK also anchors acetylcholinesterase via collagen Q, MuSK antibodies may delocalize acetylcholinesterase, helping to explain the frequent intolerance of acetylcholinesterase inhibitors in MuSK-MG. The thymus is generally normal and thymectomy is not beneficial in this subtype.[10][13]
LRP4 and Seronegative MG
- LRP4 antibodies are predominantly IgG1 (often with IgG2/IgG3), obstruct the agrin–LRP4 interaction, reduce agrin-induced MuSK activation and AChR clustering, and can also activate complement; passive transfer of patient IgG reproduces myasthenic weakness with fragmented AChR clusters in mice.[14][15]
- In seronegative MG (no AChR/MuSK antibodies on standard radioimmunoassay), cell-based assays detect clustered-AChR or MuSK antibodies in a substantial fraction, implying the same postsynaptic mechanisms with antibodies below conventional detection.[16]
- Striational and cytoplasmic antibodies (titin, ryanodine receptor, striated muscle) are biomarkers of thymoma or disease severity rather than primary pathogenic effectors and are addressed under Myasthenia gravis laboratory findings.[17]
Immunologic Dysregulation and the Thymus
- MG reflects a breakdown of self-tolerance driving CD4+ T cell–dependent B cell production of high-affinity autoantibodies in germinal centers of the thymus and lymph nodes.[18][19]
- In early-onset AChR-MG, the thymus is the site of autosensitization, showing follicular hyperplasia with ectopic germinal centers, neoangiogenesis, and chemokine overexpression (features of a tertiary lymphoid organ); thymic epithelial and myoid cells express AChR, autoreactive T and B cells and plasma cells are present, and a persistent type I interferon signature is detected. Thymoma-associated MG is nearly always AChR-positive.[20][21]
Immunogenetics
- Heritability and monozygotic concordance are approximately 35%, with HLA the strongest signal and subtype-specific associations: early-onset AChR-MG with HLA-B*08:01 (ancestral haplotype AH8.1); late-onset with HLA-DRB1*15:01/DR2/B7 and DQA1; MuSK-MG with HLA-DR14–DQ5.[22][23]
- Genome-wide association studies confirm non-HLA loci including PTPN22, CTLA4, TNIP1, and TNFRSF11A, plus the MG-specific CHRNA1 (encoding the AChR α-subunit). HLA associations differ in Asian populations (e.g., HLA-DRB1*08:03 with late-onset MG in Japanese cohorts).[23][24][25]
Associated Conditions
- Thymic abnormalities (follicular hyperplasia in early-onset AChR-MG; thymoma in ~10–15%) are strongly associated with MG; other autoimmune diseases (e.g., autoimmune thyroid disease) co-occur, particularly in early-onset disease (see Myasthenia gravis causes and Myasthenia gravis classification).[20][21]
References
- ↑ 1.0 1.1 1.2 Oved K, Denkberg G, Pinzur L, et al. (October 2025). "Subunit-Specific Immunodominance in Clinically Distinct Populations With AChR+ Myasthenia Gravis". Neurology. 105 (7). doi:10.1212/WNL.0000000000214135.
- ↑ 2.0 2.1 Huijbers MG, Marx A, Plomp JJ, Le Panse R, Phillips WD (February 2022). "Advances in the understanding of disease mechanisms of autoimmune neuromuscular junction disorders". Lancet Neurol. 21 (2): 163–175. doi:10.1016/S1474-4422(21)00357-4.
- ↑ Huijbers MG, Marx A, Plomp JJ, Le Panse R, Phillips WD (February 2022). "Advances in the understanding of disease mechanisms of autoimmune neuromuscular junction disorders". Lancet Neurol. 21 (2). doi:10.1016/S1474-4422(21)00357-4.
- ↑ Iorio R (February 2024). "Myasthenia gravis: the changing treatment landscape in the era of molecular therapies". Nat Rev Neurol. 20 (2): 84–98. doi:10.1038/s41582-023-00916-w.
- ↑ 5.0 5.1 5.2 Chamberlain JL, Huda S, Whittam DH, et al. (May 2021). "Role of complement and potential of complement inhibitors in myasthenia gravis and neuromyelitis optica spectrum disorders: a brief review". J Neurol. 268 (5): 1643–1664. doi:10.1007/s00415-020-10022-2.
- ↑ Dalakas MC, Alexopoulos H, Spaeth PJ (November 2020). "Complement in neurological disorders and emerging complement-targeted therapeutics". Nat Rev Neurol. 16 (11): 601–617. doi:10.1038/s41582-020-0400-0.
- ↑ Alfaidi N, Karmastaji S, Matic A, Bril V (June 2024). "FcRn Inhibitor Therapies in Neurologic Diseases". CNS Drugs. 38 (6): 425–441. doi:10.1007/s40263-024-01090-3.
- ↑ Yu Z, Zhang M, Jing H, et al. (September 2021). "Characterization of LRP4/Agrin Antibodies From a Patient With Myasthenia Gravis". Neurology. 97 (10): e975–e987. doi:10.1212/WNL.0000000000012463.
- ↑ Pham MC, Masi G, Patzina R, et al. (August 2023). "Individual myasthenia gravis autoantibody clones can efficiently mediate multiple mechanisms of pathology". Acta Neuropathol. 146 (2): 319–336. doi:10.1007/s00401-023-02603-y.
- ↑ 10.0 10.1 Huijbers MG, Marx A, Plomp JJ, Le Panse R, Phillips WD (February 2022). "Advances in the understanding of disease mechanisms of autoimmune neuromuscular junction disorders". Lancet Neurol. 21 (2). doi:10.1016/S1474-4422(21)00357-4.
- ↑ Keritam O, Vincent A, Zimprich F, Cetin H (2024). "A clinical perspective on muscle specific kinase antibody positive myasthenia gravis". Front Immunol. 15: 1502480. doi:10.3389/fimmu.2024.1502480. PMID 39703505 Check
|pmid=value (help). - ↑ Koneczny I, Cossins J, Waters P, Beeson D, Vincent A (2013). "MuSK myasthenia gravis IgG4 disrupts the interaction of LRP4 with MuSK but both IgG4 and IgG1-3 can disperse preformed agrin-independent AChR clusters". PLoS One. 8 (11): e80695. doi:10.1371/journal.pone.0080695. PMID 24244707.
- ↑ Kaminski HJ, Sikorski P, Coronel SI, Kusner LL (June 2024). "Myasthenia gravis: the future is here". J Clin Invest. 134 (12). doi:10.1172/JCI179742.
- ↑ Huijbers MG, Marx A, Plomp JJ, Le Panse R, Phillips WD (February 2022). "Advances in the understanding of disease mechanisms of autoimmune neuromuscular junction disorders". Lancet Neurol. 21 (2). doi:10.1016/S1474-4422(21)00357-4.
- ↑ Yu Z, Zhang M, Jing H, et al. (September 2021). "Characterization of LRP4/Agrin Antibodies From a Patient With Myasthenia Gravis". Neurology. 97 (10). doi:10.1212/WNL.0000000000012463.
- ↑ White LM, Clay FJ, Forbes AM, et al. (July 2025). "Complement inhibitors for myasthenia gravis in adults". Cochrane Database Syst Rev. 7: CD016098. doi:10.1002/14651858.CD016098.
- ↑ Truffault F, Auger L, Dragin N, et al. (June 2024). "Comparison of juvenile and adult myasthenia gravis in a French cohort with focus on thymic histology". Sci Rep. 14. doi:10.1038/s41598-024-64567-7.
- ↑ Melzer N, Ruck T, Fuhr P, et al. (August 2016). "Clinical features, pathogenesis, and treatment of myasthenia gravis: a supplement to the Guidelines of the German Neurological Society". J Neurol. 263 (8): 1473–1494. doi:10.1007/s00415-016-8045-z.
- ↑ Iorio R (February 2024). "Myasthenia gravis: the changing treatment landscape in the era of molecular therapies". Nat Rev Neurol. 20 (2). doi:10.1038/s41582-023-00916-w.
- ↑ 20.0 20.1 Huijbers MG, Marx A, Plomp JJ, Le Panse R, Phillips WD (February 2022). "Advances in the understanding of disease mechanisms of autoimmune neuromuscular junction disorders". Lancet Neurol. 21 (2). doi:10.1016/S1474-4422(21)00357-4.
- ↑ 21.0 21.1 Payet CA, You A, Fayet OM, et al. (April 2023). "Central Role of Macrophages and Nucleic Acid Release in Myasthenia Gravis Thymus". Ann Neurol. 93 (4): 643–654. doi:10.1002/ana.26551.
- ↑ Petersson M, Jons D, Feresiadou A, et al. (July 2025). "Nicotine, Alcohol Consumption, and Risk of Myasthenia Gravis". Neurology. 105 (2). doi:10.1212/WNL.0000000000213851.
- ↑ 23.0 23.1 Braun A, Shekhar S, Levey DF, et al. (November 2024). "Genome-wide meta-analysis of myasthenia gravis uncovers new loci and provides insights into polygenic prediction". Nat Commun. 15. doi:10.1038/s41467-024-53595-6.
- ↑ Ueda H, Kubota T, Goto R, et al. (March 2026). "Elucidating genetic backgrounds of myasthenia gravis in Japanese by genome-wide association studies and multi-omics analyses of thymoma". Nat Commun. 17. doi:10.1038/s41467-026-00000-0.
- ↑ Meriggioli MN, Sanders DB (May 2009). "Autoimmune myasthenia gravis: emerging clinical and biological heterogeneity". Lancet Neurol. 8 (5): 475–490. doi:10.1016/S1474-4422(09)70063-8.