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Skeie G, Bartoccioni E, Evoli A, Aarli J, Gilhus N. Ryanodine receptor antibodies are associated with severe myasthenia gravis. Eur J Neurol 2011. [DOI: 10.1111/j.1468-1331.1996.tb00205.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Vrolix K, Fraussen J, Molenaar PC, Losen M, Somers V, Stinissen P, De Baets MH, Martínez-Martínez P. The auto-antigen repertoire in myasthenia gravis. Autoimmunity 2010; 43:380-400. [PMID: 20380581 DOI: 10.3109/08916930903518073] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Myasthenia Gravis (MG) is an antibody-mediated autoimmune disorder affecting the postsynaptic membrane of the neuromuscular junction (NMJ). MG is characterized by an impaired signal transmission between the motor neuron and the skeletal muscle cell, caused by auto-antibodies directed against NMJ proteins. The auto-antibodies target the nicotinic acetylcholine receptor (nAChR) in about 90% of MG patients. In approximately 5% of MG patients, the muscle specific kinase (MuSK) is the auto-antigen. In the remaining 5% of MG patients, however, antibodies against the nAChR or MuSK are not detectable (idiopathic MG, iMG). Although only the anti-nAChR and anti-MuSK auto-antibodies have been demonstrated to be pathogenic, several other antibodies recognizing self-antigens can also be found in MG patients. Various auto-antibodies associated with thymic abnormalities have been reported, as well as many non-MG-specific auto-antibodies. However, their contribution to the cause, pathology and severity of the disease is still poorly understood. Here, we comprehensively review the reported auto-antibodies in MG patients and discuss their role in the pathology of this autoimmune disease.
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Affiliation(s)
- Kathleen Vrolix
- Division of Neuroscience, School of Mental Health and Neuroscience, Faculty of Health, Medicine and Life Sciences, Maastricht University, Maastricht, The Netherlands
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Lee EH. Ca2+ channels and skeletal muscle diseases. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2010; 103:35-43. [DOI: 10.1016/j.pbiomolbio.2010.05.003] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Revised: 03/09/2010] [Accepted: 05/19/2010] [Indexed: 11/29/2022]
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Thymoma-associated myasthenia gravis: Outcome, clinical and pathological correlations in 197 patients on a 20-year experience. J Neuroimmunol 2008; 201-202:237-44. [DOI: 10.1016/j.jneuroim.2008.07.012] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2008] [Revised: 07/17/2008] [Accepted: 07/17/2008] [Indexed: 11/17/2022]
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Romi F, Aarli JA, Gilhus NE. Myasthenia gravis patients with ryanodine receptor antibodies have distinctive clinical features. Eur J Neurol 2007; 14:617-20. [PMID: 17539937 DOI: 10.1111/j.1468-1331.2007.01785.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Myasthenia gravis (MG) is an autoimmune disease caused in 85% of the patients by acetylcholine receptor (AChR) antibodies. Non-AChR muscle antibodies, against titin and ryanodine receptor (RyR) are mainly found in sera of patients with thymoma or late-onset MG. The occurrence of RyR antibodies increases the risk for severe MG and should lead to active immunomodulating treatment already at MG onset. The aim in this study was to describe the association between symptoms at MG onset and antibody profile in 152 patients. Patients with RyR antibodies had the highest rate of bulbar, respiratory and neck involvement at MG onset. They also had the highest frequency of non-limb MG symptoms. Neck weakness occurred in 40%. Respiratory difficulties at MG onset occurred in patients with titin antibodies, with and without RyR antibodies. Patients with RyR antibodies have a distinctive non-limb MG symptom profile, with bulbar, ocular, neck, and respiratory symptoms. These features, identified as early as at the first examination by a neurologist, characterize the RyR antibody positive subgroup at MG onset.
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Affiliation(s)
- F Romi
- Department of Neurology, Haukeland University Hospital, Bergen, Norway.
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Luckman SP, Skeie GO, Helgeland G, Gilhus NE. Morphological effects of myasthenia gravis patient sera on human muscle cells. Muscle Nerve 2006; 33:93-103. [PMID: 16228972 DOI: 10.1002/mus.20443] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Myasthenia gravis (MG) is caused primarily by autoantibodies against the nicotinic acetylcholine receptor (AChR), but autoantibodies to other muscle proteins may be present. Many of these proteins have structural or signalling functions, the disruption of which may affect muscle cell morphology or viability. In order to investigate the role of such autoantibodies in MG, we examined the effect of MG patient sera, of different autoantibody composition and obtained at different stages of disease severity, on primary human muscle cells. Sera from MG patients induced changes in cell morphology from typical elongated cells to an irregular phenotype, caused the formation of inclusion bodies and intracellular vesicles, and led to a disordered arrangement of actin microfilaments. Sera from the most severely affected patients also induced cell death, which did not occur via classic apoptosis. The effects were not complement-mediated and were dose- and time-dependent. As the effects observed in the cell culture system correlated with disease severity, a greater understanding of the individual factors responsible for these effects may improve our understanding of MG pathogenesis and be of value in the assessment of disease in individual patients.
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Affiliation(s)
- Steven Paul Luckman
- Institute of Clinical Medicine, Section for Neurology, University of Bergen and Haukeland University Hospital, N5021 Bergen, Norway.
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Romi F, Kristoffersen EK, Aarli JA, Gilhus NE. The role of complement in myasthenia gravis: serological evidence of complement consumption in vivo. J Neuroimmunol 2005; 158:191-4. [PMID: 15589053 DOI: 10.1016/j.jneuroim.2004.08.002] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2004] [Revised: 08/05/2004] [Accepted: 08/05/2004] [Indexed: 12/01/2022]
Abstract
BACKGROUND Antibodies to the acetylcholine receptor (AChR) titin and the ryanodine receptor (RyR) occur in myasthenia gravis (MG). These antibodies are capable of complement activation in vitro. The involvement of the complement system should cause consumption of complement components such as C3 and C4 in vivo. MATERIALS AND METHODS Complement components C3 and C4 were assayed in sera from 78 AChR antibody-positive MG patients and 52 healthy controls. Forty-eight of the patient sera contained titin antibodies as well, and 20 were also RyR antibody-positive. RESULTS MG patients with AChR antibody concentrations above the median (11.2 nmol/l) had significantly lower mean C3 and C4 concentrations in serum compared to those with AChR antibody concentrations below the median. Titin antibody-positive MG patients, titin antibody-negative early-onset MG patients, titin antibody-negative late-onset MG patients, and controls had similar C3 and C4 concentrations. Nor did mean C3 and C4 concentrations differ in MG patients with RyR antibodies. Patients with severe MG (grades 4 and 5) had similar C3 and similar C4 levels compared to those with mild MG (grades 1 and 2). CONCLUSION An increased in vivo complement consumption was detected in MG patients with high AChR antibody concentrations, unrelated to MG severity and non-AChR muscle antibodies.
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Affiliation(s)
- Fredrik Romi
- Department of Neurology, Haukeland University Hospital, Bergen N-5021, Norway.
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Romi F, Gilhus NE, Varhaug JE, Myking A, Skeie GO, Aarli JA. Thymectomy and antimuscle antibodies in nonthymomatous myasthenia gravis. Ann N Y Acad Sci 2003; 998:481-90. [PMID: 14592917 DOI: 10.1196/annals.1254.062] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The clinical effect of thymectomy in early- and late-onset myasthenia gravis (MG) and the correlation to MG severity, pharmacological treatment, and antimuscle antibodies were examined in two series of consecutive acetylcholine receptor (AChR) antibody-positive nonthymoma MG patients. The results indicate a benefit of thymectomy in early-onset MG, but no obvious clinical benefit in late-onset MG. The presence of muscle autoantibodies did not influence the outcome of thymectomy in early-onset MG. In late-onset MG, improvement is least likely in patients with titin and/or RyR antibodies. Thymectomy should always be considered shortly after MG onset in early-onset MG patients and might only be considered in late-onset patients who have early-onset-like immunological characteristics.
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Affiliation(s)
- Fredrik Romi
- Department of Neurology, Haukeland University Hospital, N-5021 Bergen, Norway.
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Romi F, Gilhus NE, Varhaug JE, Myking A, Aarli JA. Thymectomy in nonthymoma early-onset myasthenia gravis in correlation with disease severity and muscle autoantibodies. Eur Neurol 2003; 49:210-7. [PMID: 12736536 DOI: 10.1159/000070185] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2002] [Accepted: 12/12/2002] [Indexed: 11/19/2022]
Abstract
OBJECTIVE To study the clinical effect of thymectomy in a well-defined early-onset MG subgroup and to correlate it to MG severity, the presence of circulating muscle autoantibodies, and the need for pharmacological treatment in a long-term setting. METHODS Fifty-two consecutive AChR antibody-positive early-onset MG patients (34 thymectomized and 18 nonthymectomized) were included. Severity was assessed and the pharmacological treatment monitored on a yearly basis, starting from the year of MG onset, for 5, 10, 15, and 20 consecutive years; AChR, titin, and RyR antibodies were assayed. RESULTS In the four follow-up groups, MG severity was significantly higher in nonthymectomized compared to thymectomized MG patients. The postthymectomy MG improvement was significant and persistent. There were 21/34 remissions in thymectomized patients and only 4/18 in the nonthymectomized group. Patients with initially high or low AChR antibody concentration had a similar thymectomy outcome. Only 6 patients had titin antibodies, and none had RyR antibodies. CONCLUSION The present study indicates a benefit of thymectomy in early-onset MG. The muscle autoantibody concentration does not influence the outcome of thymectomy in early-onset MG.
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Affiliation(s)
- F Romi
- Department of Neurology, Haukeland University Hospital, Bergen, Norway.
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Skeie GO, Mygland A, Treves S, Gilhus NE, Aarli JA, Zorzato F. Ryanodine receptor antibodies in myasthenia gravis: epitope mapping and effect on calcium release in vitro. Muscle Nerve 2003; 27:81-9. [PMID: 12508299 DOI: 10.1002/mus.10294] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Patients with myasthenia gravis can have antibodies against skeletal muscle ryanodine receptor (Ry1), the sarcoplasmic reticulum calcium-release channel, which plays a crucial role in excitation-contraction coupling. We have screened a panel of overlapping Ry1 fusion proteins with Ry1 antibody-containing myasthenia gravis sera to identify the main immunogenic region. The pc2 Ry1 fusion protein representing a Ry1 region close to the N-terminus (residues 799-1172) was identified as the main immunogenic region for the antibodies. The binding kinetics of the Ry1 antibodies to the pc2 Ry1 fusion protein were tested using an optical biosensor. Ry1 antibodies in the IgG fraction from sera of patients with myasthenia gravis bound with high affinity and with a stoichiometry of 1:1. The functional effect of these Ry1 antibodies was tested in an in vitro Ca2+-release assay. The Ry1 antibodies induced a twofold increase of the half-maximal concentration for 4-Cl-m-cresol-induced Ca2+ release from terminal cisternae vesicles but had no effect on V(max). The effect on 4-Cl-m-cresol-induced Ca2+ release was specific, as preincubation of the active IgG fraction with the pc2 Ry1 fusion protein abolished the inhibition. These data suggest that the Ry1 sequence defined by residues 799-1172 is involved in the regulation of Ry1 function, and that this regulation could be functionally affected in vivo in patients with myasthenia gravis.
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Affiliation(s)
- Geir Olve Skeie
- Department of Neurology, University of Bergen, N-5021 Bergen, Norway.
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Romi F, Gilhus NE, Varhaug JE, Myking A, Skeie GO, Aarli JA. Thymectomy and anti-muscle autoantibodies in late-onset myasthenia gravis. Eur J Neurol 2002; 9:55-61. [PMID: 11784377 DOI: 10.1046/j.1468-1331.2002.00352.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Thymectomy is still widely carried out in myasthenia gravis (MG) patients, but its role, especially in late-onset MG patients, is not established. These patients are immunologically heterogeneous, some with thymoma-like and others with early onset-like features. We evaluated whether any therapeutic effects of thymectomy correlate with the presence of non-acetylcholine receptor (AChR) muscle antibodies. The severity of MG, and titin and ryanodine receptor (RyR) antibodies, were assessed yearly starting from MG onset in 21 thymectomized and 22 non-thymectomized AChR antibody positive late-onset MG patients, who were followed for 2, 3 and 5 years. Clinical or pharmacological remission were seen in six of 11 titin antibody negative but none of the 10 titin antibody positive thymectomized patients, however, the non-thymectomized cases showed an opposite trend. The three MG-related deaths were all in patients with titin antibodies. There was no significant difference in MG severity between thymectomized and non-thymectomized patients; 2 years after MG onset, both groups were significantly improved. This study showed no dramatic benefit from thymectomy in late-onset MG in general. Any limited improvement appeared less likely in cases with titin and/or RyR antibodies.
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Affiliation(s)
- F Romi
- Department of Neurology, Haukeland University Hospital, Bergen, Norway.
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Skeie GO, Lunde PK, Sejersted OM, Mygland A, Aarli JA, Gilhus NE. Autoimmunity against the ryanodine receptor in myasthenia gravis. ACTA PHYSIOLOGICA SCANDINAVICA 2001; 171:379-84. [PMID: 11412151 DOI: 10.1046/j.1365-201x.2001.00841.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Some myasthenia gravis (MG) patients have antibodies against skeletal muscle antigens in addition to the acetylcholine receptor (AChR). A major antigen for these antibodies is the Ca2+ release channel of the sarcoplasmic reticulum the ryanodine receptor (RyR). These antibodies are found mainly in MG patients with a thymoma MG and correlate with severe MG symptoms. The antibodies recognize a region near the N-terminus on the RyR, which seems to be of importance for RyR regulation. The antibodies cause allosteric inhibition of RyR function in vitro, inhibiting Ca2+ release from sarcoplasmic reticulum.
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Affiliation(s)
- G O Skeie
- Department of Neurology, University of Bergen, Bergen, Norway
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Romi F, Skeie GO, Vedeler C, Aarli JA, Zorzato F, Gilhus NE. Complement activation by titin and ryanodine receptor autoantibodies in myasthenia gravis. A study of IgG subclasses and clinical correlations. J Neuroimmunol 2000; 111:169-76. [PMID: 11063835 DOI: 10.1016/s0165-5728(00)00394-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
To elucidate the mechanism of immune damage caused by titin and ryanodine receptor (RyR) autoantibodies in myasthenia gravis (MG), we studied the complement-activating capacity and the IgG subclass distribution of these autoantibodies in sera from 49 MG patients. Complement activation occurred in 38 out of 49 titin antibody positive sera, and in 14 out of 21 RyR antibody positive sera. The titin antibodies occurred only in the IgG 1 and IgG 4 subclasses, whereas the RyR antibodies occurred in all four IgG subclasses but with IgG 1 predominance. Complement-activating RyR antibodies occurred with higher frequency in sera of thymoma MG than of late-onset MG. RyR IgG 1 antibodies occurred more often in severe MG than in mild and moderate disease groups. Mean total IgG and IgG 1 titin and RyR antibody titers fell during long-time patient observation together with an improvement of the MG symptoms.
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Affiliation(s)
- F Romi
- Department of Neurology, Haukeland University Hospital, N-5021, Bergen, Norway.
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Baggi F, Andreetta F, Antozzi C, Simoncini O, Confalonieri P, Labeit S, Cornelio F, Mantegazza R. Anti-titin and antiryanodine receptor antibodies in myasthenia gravis patients with thymoma. Ann N Y Acad Sci 1998; 841:538-41. [PMID: 9668290 DOI: 10.1111/j.1749-6632.1998.tb10978.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- F Baggi
- Department of Neuromuscular Diseases, National Neurological Institute C. Besta, Milan, Italy
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Aarli JA, Skeie GO, Mygland A, Gilhus NE. Muscle striation antibodies in myasthenia gravis. Diagnostic and functional significance. Ann N Y Acad Sci 1998; 841:505-15. [PMID: 9668283 DOI: 10.1111/j.1749-6632.1998.tb10971.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- J A Aarli
- Department of Neurology, Haukeland Hospital, University of Bergen, Norway
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Skeie GO, Pandey JP, Aarli JA, Gilhus NE. Autoimmunity to ryanodine receptor and titin in myasthenia gravis is associated with GM allotypes. Autoimmunity 1998; 26:111-6. [PMID: 9546812 DOI: 10.3109/08916939709003854] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Myasthenia gravis (MG) is mediated by autoantibodies against the acetylcholine receptor at the muscle endplate. Some MG patients have in addition antibodies (Ab) to the skeletal muscle proteins ryanodine receptor (RyR) and titin. We have examined GM and KM allotypes, RyR and titin Ab in 44 MG patients (37 thymoma patients and 7 non-thymoma, late-onset patients) and 292 non-MG controls to see if GM/KM allotypes associate with differences in autoantibody production. All patients had titin Ab, and 15 thymoma patients had also RyR Ab. The phenotype GM 1, 2, 3 23 5, 21 was significantly increased in the patients with titin Ab compared with the non-MG controls (chi2 = 4.93, p < 0.05). Thymoma patients with RyR Ab had a higher frequency of the GM 3 23 5 phenotype compared with RyR Ab negative patients and controls (chi2 = 7.1, p < 0.05). KM allotypes did not differ between RyR Ab positive or titin Ab positive patients and controls. GM phenotypes may thus be associated with an autoimmune response against the muscle proteins titin and RyR in MG patients.
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Affiliation(s)
- G O Skeie
- Department of Neurology, University of Bergen, Norway
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Skeie GO, Lunde PK, Sejersted OM, Mygland A, Aarli JA, Gilhus NE. Myasthenia gravis sera containing antiryanodine receptor antibodies inhibit binding of [3H]-ryanodine to sarcoplasmic reticulum. Muscle Nerve 1998; 21:329-35. [PMID: 9486861 DOI: 10.1002/(sici)1097-4598(199803)21:3<329::aid-mus6>3.0.co;2-c] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Myasthenia gravis (MG) patients with thymoma often have antibodies against the calcium-release channel of the sarcoplasmic reticulum (SR) in striated muscle, the ryanodine receptor (RyR). RyR function can be tested in vitro by measuring the degree of [3H]-ryanodine binding to SR. In this study, sera from 9 out of 14 MG patients containing RyR antibodies inhibited [3H]-ryanodine binding to SR membranes from rat skeletal muscle. The 9 patients with antibodies inhibiting ryanodine binding had more severe MG than those with noninhibiting antibodies (P = 0.006). Sera from MG patients with acetylcholine receptor and titin muscle antibodies but no antibodies against RyR and blood-donor sera did not have an inhibiting effect in the [3H]-ryanodine binding assay. The results show that RyR antibodies in MG patients have high affinity for the RyR, and that the binding of antibodies probably affects calcium release from SR by locking the RyR ion channel in a closed position.
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Affiliation(s)
- G O Skeie
- Department of Neurology, University of Bergen, Norway
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Abstract
Calcium signalling in cells is dependent on a communication between channels/ transporters in two membrane structures: the cell membrane and the membranes of endo- and sarcoplasmic reticula (ER/SR). In general, cytosolic Ca2+ can be raised by influx of calcium over the cell membrane through three types of channels: voltage-, receptor-, and store-operated channels (VOCs, ROCs and SOCs). This small Ca2+ influx is most often amplified by a Ca2+ release from the ER/SR through two types of channels: the IP3-receptor and the ryanodine receptor (RyR), which are huge proteins identified and cloned in recent years. We focus on the 'synaptic' connection between VOCs (L-type calcium channels) and RyRs of the SR in heart and skeletal muscle. Depolarization of the cell membrane (an action potential) opens the VOC and moves it in the membrane. One VOC triggers opening of a certain number of underlying RyRs that together release a quantum of calcium from the SR, a calcium spark. The communication between the VOC and RyRs is probably achieved primarily by a mechanical link in skeletal muscle (voltage-controlled calcium release), and by the small inward calcium flux through the VOC in the heart (calcium-induced calcium release, CICR). Conditions as different as heart failure, myasthenia gravis, malignant hyperthermia, and skeletal muscle fatigue, may be examples of deteriorated control or function of the RyR.
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Affiliation(s)
- P K Lunde
- University of Oslo, Ullevaal Hospital, Norway
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Hoedemaekers AC, van Breda Vriesman PJ, De Baets MH. Myasthenia gravis as a prototype autoimmune receptor disease. Immunol Res 1997; 16:341-54. [PMID: 9439759 DOI: 10.1007/bf02786398] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Myasthenia gravis (MG) is an organ-specific autoimmune disease in which autoantibodies against nicotinic acetylcholine receptors (AChR) at the postsynaptic membrane cause loss of functional AChR and disturbed neuromuscular transmission. The immunopathogenic mechanisms responsible for loss of functional AChR include antigenic modulation by anti-AChR antibodies, complement-mediated focal lysis of the postsynaptic membrane, and direct interference with binding of acetylcholine to the AChR or with ion channel function. The loss of AChR and subsequent defective neuromuscular transmission is accompanied by increased expression of the different AChR subunit genes, suggesting a role for the target organ itself in determining susceptibility and severity of disease. Experimental autoimmune myasthenia gravis (EAMG) is an animal model for the disease MG, and is very suitable to study the immunopathogenic mechanisms leading to AChR loss and the response of the AChR to this attack. In this article the current concepts of the structure and function of the AChR and the immunopathological mechanisms in MG and EAMG are reviewed.
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Affiliation(s)
- A C Hoedemaekers
- Department of Immunology, Maastricht University, Maastricht, The Netherlands
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Gigliotti D, Lefvert AK, Jeddi-Tehrani M, Esin S, Hodara V, Pirskanen R, Wigzell H, Andersson R. Overexpression of Select T Cell Receptor Vβ Gene Families within CD4+ and CD8+ T Cell Subsets of Myasthenia Gravis Patients: A Role for Superantigen(s)? Mol Med 1996. [DOI: 10.1007/bf03401904] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
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Mygland A, Kuwajima G, Mikoshiba K, Tysnes OB, Aarli JA, Gilhus NE. Thymomas express epitopes shared by the ryanodine receptor. J Neuroimmunol 1995; 62:79-83. [PMID: 7499495 DOI: 10.1016/0165-5728(95)00106-c] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Myasthenia gravis (MG) patients with thymoma have antibodies against ryanodine receptor (RyR) of skeletal and heart muscle. In this study, thymomas were examined for reactivity with a panel of polyclonal rabbit antibodies against various short peptides of RyR. An antibody against peptide C2 in the transmembrane region of RyR stained thymoma epithelial cells in cryosections of 17/23 thymomas, and detected a 40-kDa peptide in Western blotting of a thymoma membrane fraction. The other RyR antibodies did not react with thymoma tissue. The anti-C2 RyR antibody did not react with normal thymus, tonsil or carcinoma of colon. The results strongly indicate that epithelial thymoma cells express an epitope shared by the transmembrane region of skeletal and cardiac muscle RyR.
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Affiliation(s)
- A Mygland
- Department of Neurology, University of Bergen, Norway
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Skeie GO, Mygland A, Aarli JA, Gilhus NE. Titin antibodies in patients with late onset myasthenia gravis: clinical correlations. Autoimmunity 1995; 20:99-104. [PMID: 7578874 DOI: 10.3109/08916939509001933] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We have tested sera from 21 thymectomized patients with onset of MG after 40 years of age and without thymoma for antibodies against titin, using ELISA with the titin peptide MGT-30. Titin is a myofibrillar protein unique to striated muscle and important for the elastic recoil of muscle cells. Titin antibodies were detected in 9 of the 21 sera. MG symptoms as assessed by a 6 point disability score (0-5) were significantly more severe in the titin antibody positive patients both at peak of illness; 3.7 vs. 3.1 (p < 0.02) and at latest follow up; 2.1 vs. 0.8 (p < 0.01). All titin antibody positive patients were on immunosuppressive drug treatment at least follow-up, whereas only 3 of 12 patients without titin antibodies used immunosuppressive drugs. The presence of circulating titin antibodies in late-onset non-thymoma MG patients indicates a more severe disease.
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Affiliation(s)
- G O Skeie
- Department of Neurology, University of Bergen, Norway
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25
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Mygland A, Aarli JA, Matre R, Gilhus NE. Ryanodine receptor antibodies related to severity of thymoma associated myasthenia gravis. J Neurol Neurosurg Psychiatry 1994; 57:843-6. [PMID: 8021674 PMCID: PMC1073029 DOI: 10.1136/jnnp.57.7.843] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Ryanodine receptor (RyR) antibodies are detected in about 50% of patients with myasthenia gravis who have a thymoma. The RyR is a calcium release channel involved in the mechanism of excitation-contraction coupling in striated muscle. In this study the severity of myasthenia gravis assessed by a five point disability score was compared between 12 patients with myasthenia gravis, a thymoma, and RyR antibodies and 10 patients with myasthenia gravis and a thymoma but without such antibodies. Symptoms of myasthenia gravis were significantly more severe in patients with RyR antibodies. The mean (SD) disability scores were 3.7(0.5) in patients with antibodies and 2.7 (0.9) in those without at peak of illness, (p = 0.01) and 3.4(1.4) v 1.6(0.7) at the end of an average observation period of five years (p = 0.002). The number of deaths due to myasthenia gravis was five of 12 RyR antibody positive patients, and none of 10 RyR antibody negative patients (p = 0.04). RyR antibody levels correlated positively with severity of myasthenia gravis. The presence of circulating RyR antibodies seems to be associated with a severe form of thymoma associated myasthenia gravis.
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Affiliation(s)
- A Mygland
- Department of Neurology, Gade Institute, University of Bergen, Norway
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26
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Mygland A, Tysnes OB, Matre R, Aarli JA, Gilhus NE. Anti-cardiac ryanodine receptor antibodies in thymoma-associated myasthenia gravis. Autoimmunity 1994; 17:327-31. [PMID: 7948615 DOI: 10.3109/08916939409010673] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Sera from myasthenia gravis (MG) patients with thymoma were examined in Western blot for the presence of antibodies to proteins in the sarcoplasmic reticulum (SR) of cardiac muscle. Fourteen of 30 MG thymoma sera had IgG antibodies to a protein with the same electrophoretic mobility as cardiac muscle ryanodine receptor (RyR). Anti-cardiac RyR antibodies were not detected in any of the 45 sera from MG patients without thymoma. The same 14 MG thymoma sera, but none of the others, bound to RyR from skeletal muscle as well. Neutralization experiments showed that the anti-RyR antibodies in MG patient cross-reacted with cardiac and skeletal muscle RyR. Since skeletal and cardiac muscle RyRs are antigenically different, our findings may indicate that autoantibodies to RyR in MG originate by sensitization to a peptide shared by cardiac and skeletal muscle RyR, rather than to the complete native RyR.
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Affiliation(s)
- A Mygland
- Department of Neurology, Gade Institute, University of Bergen, Norway
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27
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Conti-Tronconi BM, McLane KE, Raftery MA, Grando SA, Protti MP. The nicotinic acetylcholine receptor: structure and autoimmune pathology. Crit Rev Biochem Mol Biol 1994; 29:69-123. [PMID: 8026215 DOI: 10.3109/10409239409086798] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The nicotinic acetylcholine receptors (AChR) are presently the best-characterized neurotransmitter receptors. They are pentamers of homologous or identical subunits, symmetrically arranged to form a transmembrane cation channel. The AChR subunits form a family of homologous proteins, derived from a common ancestor. An autoimmune response to muscle AChR causes the disease myasthenia gravis. This review summarizes recent developments in the understanding of the AChR structure and its molecular recognition by the immune system in myasthenia.
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Affiliation(s)
- B M Conti-Tronconi
- Department of Biochemistry, College of Biological Sciences, University of Minnesota, St. Paul 55108
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28
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Protti MP, Manfredi AA, Horton RM, Bellone M, Conti-Tronconi BM. Myasthenia gravis: recognition of a human autoantigen at the molecular level. IMMUNOLOGY TODAY 1993; 14:363-8. [PMID: 8363727 DOI: 10.1016/0167-5699(93)90237-f] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The symptoms of myasthenia gravis are primarily or exclusively due to an autoimmune response against the muscle nicotinic acetylcholine receptor (AChR) and this has been the object of intensive investigations for almost 20 years. A detailed picture at the molecular level of the interaction of this autoantigen with the key elements involved in the autoimmune response, such as anti-AChR antibodies, the T-cell receptor and restricting major histocompatibility complex molecules, is now emerging for both human myasthenia gravis and its experimental model, experimental autoimmune myasthenia gravis. Here, Maria Pia Protti and colleagues focus on the molecular interactions occurring in human myasthenia gravis and summarize recent information on pathogenic mechanisms of the autoimmune response, and the structure of epitopes recognized by B cells and CD4+ T cells of myasthenic patients on the AChR molecule.
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Affiliation(s)
- M P Protti
- Medicina II Department, Scientific Institute San Raffaele, Milano, Italy
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29
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Mygland A, Tysnes OB, Matre R, Volpe P, Aarli JA, Gilhus NE. Ryanodine receptor autoantibodies in myasthenia gravis patients with a thymoma. Ann Neurol 1992; 32:589-91. [PMID: 1333745 DOI: 10.1002/ana.410320419] [Citation(s) in RCA: 111] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Sera from patients with myasthenia gravis were examined by Western blot for the presence of antibodies to proteins of the sarcoplasmic reticulum from rabbit skeletal muscle. Fourteen of 30 patients with myasthenia gravis and a thymoma had IgG autoantibodies to the calcium release channel of the sarcoplasmic reticulum (the ryanodine receptor), which plays a crucial role in the mechanism of excitation-contraction coupling in striated muscle. Ryanodine receptor autoantibodies were not detected in any of the 45 sera from patients with myasthenia gravis without a thymoma. Ryanodine receptor autoantibodies may have pathogenetic relevance in thymoma-associated myasthenia gravis.
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Affiliation(s)
- A Mygland
- Department of Neurology, University of Bergen, Norway
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