Antibodies against the main immunogenic region of the acetylcholine receptor correlate with disease severity in myasthenia gravis

Department of Clinical Neuroscience and Neurology, Graduate School of Biomedical Sciences, Nagasaki University, Japan.
Journal of neurology, neurosurgery, and psychiatry (Impact Factor: 6.81). 07/2012; 83(9):935-40. DOI: 10.1136/jnnp-2012-302705
Source: PubMed


We developed an assay that detects autoantibodies against the main immunogenic region (MIR) located at the extracellular end of the nicotinic acetylcholine receptor (AChR) α subunit, and investigated its clinical relevance in myasthenia gravis (MG).
In this retrospective cohort study, we measured MIR antibody (Ab) titres in sera obtained before treatment and analysed their associations with clinical parameters in 102 MG patients from two neurological centres. MIR Ab titres were determined using a modified competition immunoprecipitation assay in the presence or absence of monoclonal antibody 35.
11 of 23 (47.8%) ocular type and 66 of 72 (91.7%) generalised type MG patients were positive for the presence of MIR Abs, defined as a titre >16.8% (3 SDs above the mean for 70 healthy controls). A significantly higher MIR Ab titre (p<0.001) was shown in generalised type (47.9±19.2%) rather than in ocular type MG patients (16.4±8.4%). Bivariate regression analysis using both titre levels of MIR Ab and routine AChR binding Ab as variables revealed MIR Abs to be an exclusive indicator positively associated with disease severity (Myasthenia Gravis Foundation of America classification, p<0.0001; Quantitative MG score, p=0.008), the presence of bulbar symptoms (p<0.0001) and thymoma (p=0.016), and negatively associated with ocular MG (p<0.0001).
MIR Ab titre levels show much better correlations with factors related to disease severity compared with AChR binding Ab titres. The MIR Ab assay may be useful for predicting MG symptom severity, especially for discriminating between ocular and generalised types of MG.

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    • "However, no studies have correlated antiAChR antibody titers with MG severity. A retrospective study showed that antibodies against the main immunogenic region of AChR differentiate between ocular and generalized MG[58], but large, prospective studies addressing the correlation of antiAChR antibody titers and disease severity are lacking. "
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    ABSTRACT: THIS IS NOT THE FINAL POST-PRINT VERSION. To get full post-print version, please, go to Myasthenic disorders are a well characterized group of diseases of the neuromuscular junction. Their pathogenesis is diverse, including genetic and autoimmune mechanisms. We review recent findings on risk factors, pathogenesis and treatment of autoimmune myasthenia gravis. Better knowledge of congenital myasthenia has led to the development of efficient diagnostic algorithms that have therapeutic implications. New epidemiological and genetic risk factors have been identified and are considered to play a role in the development of myasthenia gravis. The study of the role of innate immunity in myasthenia gravis has identified relevant pathways to explain myasthenia gravis causes. The description of the pathogenic role of IgG4 anti-MuSK antibodies has revealed heterogeneous immune mechanisms that should lead to more specific therapies. Rituximab seems to be particularly effective in MuSK myasthenia gravis, and eculizumab arises as an option in refractory AChR myasthenia gravis. Therapeutic algorithms need to be tailored to each myasthenia subtype. Increasing knowledge about the environmental and genetic risk factors and basic immunopathogenesis of myasthenia gravis, including the role of innate immunity, regulatory T cell impairment and autoantibody heterogeneity, is providing a rationale for treatment with new biological agents. Current immunotherapies in myasthenia gravis undoubtedly provide benefits, but also cause side-effects. Controlled trials are, therefore, needed to confirm initial results from pilot studies.
    Current opinion in neurology 08/2013; DOI:10.1097/WCO.0b013e328364c079 · 5.31 Impact Factor
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    ABSTRACT: Myasthenia gravis is caused by antibodies to the acetylcholine receptor, muscle-specific kinase, low-density lipoprotein receptor-related protein 4, or possibly yet unidentified antibodies. The mechanisms by which these antibodies interfere with the function of postsynaptic proteins include complement activation, antigenic modulation by crosslinking of the target proteins, competition with ligand binding sites, or steric hindrance which inhibits conformational changes or binding to associated proteins. Screening for auto-antibodies to different postsynaptic targets, and also for low-affinity antibodies, is contributing to a more accurate diagnosis of MG patients. Further studies into the specific pathophysiological pathways of the several MG subforms might help to develop new, more antigen specific, therapies.
    Autoimmunity reviews 03/2013; 12(9). DOI:10.1016/j.autrev.2013.03.001 · 7.93 Impact Factor
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    ABSTRACT: Abstract Myasthenia gravis (MG) is caused by the failure of neuromuscular transmission mediated by pathogenic autoantibodies (Abs). Generally, patients with MG are divided into 3 groups: (1) nicotinic acetylcholine receptor antibody-positive MG (AChR-MG: 80%), (2) muscle-specific receptor tyrosine kinase antibody-positive MG (MuSK-MG: 5-10%), which are AChR-associated transmembrane post-synaptic proteins involved in AChR aggregation, and (3) double-seronegative MG. In 2011, autoantibodies against low-density lipoprotein receptor-related protein 4 (Lrp4) were identified in Japanese MG patients, and thereafter, have been reported in Germany and USA. We developed a simple technique termed Gaussia luciferase immunoprecipitation (GLIP) for detecting the antibodies to Lrp4. Our results showed that 9 generalized MG patients out of 300 without AChR Ab were positive for Lrp4 antibodies. These antibodies inhibit the binding of Lrp4 to its ligand and predominantly belong to the IgG1 subclass. In other studies, Lrp4 Ab-positive sera inhibited agrin-induced aggregation of AChRs in cultured myotubes, suggesting a pathogenic role in the dysfunction of the neuromuscular endplate. Further understanding of the structure and function of neuromuscular junction (NMJ) through newly discovered autoantibodies may provide specific clinical information and treatment for MG.
    Brain and nerve = Shinkei kenkyū no shinpo 04/2013; 65(4):433-9.
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