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.
"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, but large, prospective studies addressing the correlation of antiAChR antibody titers and disease severity are lacking. "
[Show abstract][Hide abstract] ABSTRACT: THIS IS NOT THE FINAL POST-PRINT VERSION. To get full post-print version, please, go to http://journals.lww.com/co-neurology/pages/articleviewer.aspx?year=2013&issue=10000&article=00003&type=abstract
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
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: The differences in the characteristics of thymus histology, coexisting autoimmune diseases and related autoantibodies between anti-muscle-specific receptor tyrosine kinase (MuSK)-antibody (Ab)-positive myasthenia gravis (MG) patients, and anti-acetylcholine receptor (AChR)-Ab-positive MG patients are not clearly defined.
The types of thymus histology, coexisting autoimmune diseases and associated Abs in 83 MuSK-Ab-positive patients nationwide were investigated and were compared with those in AChR-Ab-positive patients followed at our institute (n = 83). As for the autoantibodies associated with thymoma, titin Abs were measured.
Thymoma was not present in any of the MuSK-Ab-positive patients but presented in 21 patients (25.3%) amongst the AChR-Ab-positive patients. Titin Abs were absent in MuSK-Ab-positive patients but positive in 25 (30.1%) of the AChR-Ab-positive patients. Concomitant autoimmune diseases were present in eight MuSK-Ab-positive patients (9.6%) amongst whom Hashimoto's thyroiditis and rheumatoid arthritis predominated, whereas 22 AChR-Ab-positive patients (26.5%) had one or more concomitant autoimmune diseases of which Graves' disease predominated.
Differences in frequency of thymoma and thymic hyperplasia, coexisting autoimmune diseases and autoantibody positivity between MuSK-Ab-positive and AChR-Ab-positive MG were indicated, suggesting that, in contrast with AChR-Ab-positive MG, thymus does not seem to be involved in the pathogenic mechanisms of MuSK-Ab-positive MG.
European Journal of Neurology 05/2013; 20(9). DOI:10.1111/ene.12169 · 4.06 Impact Factor
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