11th International Conference on Myasthenia Gravis and Related Disorders
Posted September 06, 2007
Myasthenia gravis (MG) is a neuromuscular disease characterized by fluctuating muscle weakness with fatigability. This weakness chiefly affects the oculofacial muscles and the proximal skeletal muscles. MG is marked by exacerbations and remission, and some patients experience severe, life-threatening weakness that can require intubation with mechanical ventilation. Myasthenia gravis is among the best understood autoimmune diseases and is one of the only ones—if not the only one—that fulfills strict criteria for autoimmunity.
Since 1954 the New York Academy of Sciences has been cosponsoring international conferences on MG as a way for researchers in this field to stay current with new developments and to exchange ideas. At the 2007 meeting researchers presented findings on a broad range of basic and clinical topics. This was a particularly dynamic conference, since many important advances have been made in the last several years regarding both pathogenesis and therapy.
Use the tabs above to find a meeting report and multimedia from this event.
Slide and audio presentations available from:
Chien-Ping Ko (University of Southern California)
Gil I. Wolfe (University of Texas Southwestern Medical Center)
Amelia Evoli (Catholic University, Rome)
Bruno Kyewski (German Cancer Research Center, Heidelberg)
Henry J. Kaminski (Saint Louis University)
Richard J. Barohn (University of Kansas Medical Center)
Johan A. Aarli (University of Bergen, Norway)
Donald B. Sanders (Duke University Medical Center)
Jon Sussman (Greater Manchester Neuroscience Centre)
Myasthenia Gravis Foundation of America
The only national volunteer health agency dedicated solely to the fight against myasthenia gravis. Learn more about myasthenia gravis, or see information for patients and healthcare professionals.
Links to additional information about MG from the National Library of Medicine.
National Institute of Neurological Disorders and Stroke
Fact sheet on myasthenia gravis.
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Structure of neuromuscular junction and acetylcholine receptor
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Muscle-specific kinase (MuSK) myasthenia
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Hatanaka Y, Hemmi S, Morgan MB, et al. 2005. Nonresponsiveness to anticholinesterase agents in patients with MuSK-antibody-positive MG. Neurology 65: 1508-1509.
Hoch W, McConville J, Helms S, et al. 2001. Auto-antibodies to the receptor tyrosine kinase MuSK in patients with myasthenia gravis without acetylcholine receptor antibodies. Nat. Med. 7: 365-368.
Lin PT, Martin BA, Weinacker AB, So YT. 2006. High-dose cyclophosphamide in refractory myasthenia gravis with MuSK antibodies. Muscle Nerve 33: 433-435.
Liyanage Y, Hoch W, Beeson D, Vincent A. 2002. The agrin/muscle-specific kinase pathway: new targets for autoimmune and genetic disorders at the neuromuscular junction. Muscle Nerve 25: 4-16.
Sanders DB, El-Salem K, Massey JM, et al. 2003. Clinical aspects of MuSK antibody positive seronegative MG. Neurology 60: 1978-1980.
Shigemoto K, Kubo S, Maruyama N, et al. 2006. Induction of myasthenia by immunization against muscle-specific kinase. J. Clin. Invest. 116: 1016-1024. Full Text
Congenital myasthenic syndromes
Burke G, Cossins J, Maxwell S, et al. 2004. Distinct phenotypes of congenital acetylcholine receptor deficiency. Neuromuscul. Disord. 14: 356-364.
Engel AG, Sine SM. 2005. Current understanding of congenital myasthenic syndromes. Curr. Opin. Pharmacol. 5: 308-321.
Müller JS, Herczegfalvi A, Vilchez JJ, et al. 2007. Phenotypical spectrum of DOK7 mutations in congenital myasthenic syndromes. Brain 130: 1497-1506.
Slater CR, Fawcett PR, Walls TJ, et al. 2006. Pre- and post-synaptic abnormalities associated with impaired neuromuscular transmission in a group of patients with 'limb-girdle myasthenia'. Brain 129: 2061-2076.
Irish JM, Hovland R, Krutzik PO, et al. 2004. Single cell profiling of potentiated phospho-protein networks in cancer cells. Cell 118: 217-228.
Krutzik PO, Hale MB, Nolan GP. 2005. Characterization of the murine immunological signaling network with phosphospecific flow cytometry. J. Immunol. 175: 2366-2373. Full Text
Krutzik PO, Nolan GP. 2006. Fluorescent cell barcoding in flow cytometry allows high-throughput drug screening and signaling profiling. Nat. Methods 3: 361-368.
Sachs K, Perez O, Pe'er D, et al. 2005. Causal protein-signaling networks derived from multiparameter single-cell data. Science 308: 523-529.
Immunology of AIDs involving neuronal and glial channel proteins
Lennon VA, Ermilov LG, Szurszewski JH, Vernino S. 2003. Immunization with neuronal nicotinic acetylcholine receptor induces neurological autoimmune disease. J. Clin. Invest. 111: 907-913. Full Text
Schroeder C, Vernino S, Birkenfeld AL, et al. 2005. Plasma exchange for primary autoimmune autonomic failure. N. Engl. J. Med. 353: 1585-1590.
Vernino S, Cheshire WP, Lennon VA. 2001. Myasthenia gravis with autoimmune autonomic neuropathy. Auton. Neurosci. 88: 187-192.
Vernino S, Ermilov LG, Sha L, et al. 2004. Passive transfer of autoimmune autonomic neuropathy to mice. J. Neurosci. 24: 7037-7042. Full Text
Vernino S, Low PA, Fealey RD, et al. 2000. Autoantibodies to ganglionic acetylcholine receptors in autoimmune autonomic neuropathies. N. Engl. J. Med. 343: 847-855.
Verschuuren JJ, Wirtz PW, Titulaer MJ, et al. 2006. Available treatment options for the management of Lambert-Eaton myasthenic syndrome. Expert Opin. Pharmacother. 7: 1323-1336.
Wirtz PW, Willcox N, van der Slik AR, et al. 2005. HLA and smoking in prediction and prognosis of small cell lung cancer in autoimmune Lambert-Eaton myasthenic syndrome. J. Neuroimmunol. 159: 230-237.
Wirtz PW, Wintzen AR, Verschuuren JJ. 2005. Lambert-Eaton myasthenic syndrome has a more progressive course in patients with lung cancer. Muscle Nerve 32: 226-229.
Autoimmune pathogenesis of MG: current concepts
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DeVoss J, Jou Y, Johannes K, et al. 2006. Spontaneous autoimmunity prevented by thymic expression of a single self-antigen. J. Exp. Med. 203: 2727-2735. Full Text
Klamp T, Sahin U, Kyewski B, et al. 2006. Expression profiling of autoimmune regulator AIRE mRNA in a comprehensive set of human normal and neoplastic tissues. Immunol. Lett. 106: 172-179.
Klein L, Kyewski B. 2006. A central role for central tolerance. Annu. Rev. Immunol. 24: 571-606.
Kaminski JH, Li Z, Richmonds C, et al. 2004. Complement regulators in extraocular muscle and experimental autoimmune myasthenia gravis. Exp. Neurol. 189: 333-342.
Kaminski HJ, Kusner LL, Richmonds C, et al. 2006. Deficiency of decay accelerating factor and CD59 leads to crisis in experimental myasthenia. Exp. Neurol. 202: 287-293.
Karachunski PI, Ostlie NS, Monfardini C, Conti-Fine BM. 2000. Absence of IFN-γ or IL-12 has different effects on experimental myasthenia gravis in C57BL/6 mice. J. Immunol. 164: 5236-5244. Full Text
Ostlie N, Milani M, Wang W, et al. 2003. Absence of IL-4 facilitates the development of chronic autoimmune myasthenia gravis in C57BL/6 mice. J. Immunol. 170: 604-612. Full Text
Tüzün E, Li J, Saini SS, et al. 2007. Pros and cons of treating murine myasthenia gravis with anti-C1q antibody. J. Neuroimmunol. 182: 167-176.
Tüzün E, Scott BG, Goluszko E, et al. 2003. Genetic evidence for involvement of classical complement pathway in induction of experimental autoimmune myasthenia gravis. J. Immunol. 171: 3847-3854. Full Text
Wang W, Milani M, Ostlie N, et al. 2007. C57BL/6 mice genetically deficient in IL-12/IL-23 and IFN-gamma are susceptible to experimental autoimmune myasthenia gravis, suggesting a pathogenic role of non-Th1 cells. J. Immunol. 178: 7072-7080.
Gronseth GS, Barohn RJ. 2000. Practice parameter: thymectomy for autoimmune myasthenia gravis (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology 55: 7-15.
Matsuda M, Dohi-Iijima N, Nakamura A, et al. 2005. Increase in incidence of elderly-onset patients with myasthenia gravis in Nagano Prefecture, Japan. Intern. Med. 44: 572-577. Full Text
Palace J, Newsom-Davis J, Lecky B. 1998. A randomized double-blind trial of prednisolone alone or with azathioprine in myasthenia gravis. Myasthenia Gravis Study Group. Neurology 50: 1778-1783.
Tindall RS, Rollins JA, Phillips JT, et al. 1987. Preliminary results of a double-blind, randomized, placebo-controlled trial of cyclosporine in myasthenia gravis. N. Engl. J. Med. 316: 719-724.
Somnier FE, Keiding N, Paulson OB. 1991. Epidemiology of myasthenia gravis in Denmark. A longitudinal and comprehensive population survey. Arch. Neurol. 48: 733-739.
Completed clinical trials
Dalakas MC. 2004. Intravenous immunoglobulin in autoimmune neuromuscular diseases. JAMA 291: 2367-2375.
Gajdos P, Chevret S, Clair B, et al. 1997. Clinical trial of plasma exchange and high-dose intravenous immunoglobulin in myasthenia gravis. Myasthenia Gravis Clinical Study Group. Ann. Neurol. 41: 789-796.
Qureshi AI, Choudhry MA, Akbar MS, et al. 1999. Plasma exchange versus intravenous immunoglobulin treatment in myasthenic crisis. Neurology 52: 629-632.
Zinman L, Ng E, Bril V. 2007. IV immunoglobulin in patients with myasthenia gravis: a randomized controlled trial. Neurology 68: 837-841.
Clinical trials in progress
Brenner T, Hamra-Amitay Y, Evron T, et al. 2003. The role of readthrough acetylcholinesterase in the pathophysiology of myasthenia gravis. FASEB J. 17: 214-222. Full Text
Desai SB, Furst DE. 2006. Problems encountered during anti-tumor necrosis factor therapy. Best Pract. Res. Clin. Rheumatol. 20: 757-790.
Drachman DB, Brodsky RA. 2005. High-dose therapy for autoimmune neurologic diseases. Curr. Opin. Oncol. 17: 83-88.
Drachman DB, Jones RJ, Brodsky RA. 2003. Treatment of refractory myasthenia: "rebooting" with high-dose cyclophosphamide. Ann. Neurol. 53: 29-34.
Monsul NT, Patwa HS, Knorr AM, et al. 2004. The effect of prednisone on the progression from ocular to generalized myasthenia gravis. J. Neurol. Sci. 217: 131-133.
Rowin J, Meriggioli MN, Tüzün E, et al. 2004. Etanercept treatment in corticosteroid-dependent myasthenia gravis. Neurology 63: 2390-2392.
Sommer N, Sigg B, Melms A, et al. 1997. Ocular myasthenia gravis: response to long-term immunosuppressive treatment. J. Neurol. Neurosurg. Psychiatry 62: 156-162.
Thymectomy for MG
Jaretzki A, Steinglass KM, Sonett JR. 2004. Thymectomy in the management of myasthenia gravis. Semin. Neurol. 24: 49-62.
Zielinski M, Kuzdzal J, Szlubowski A, Soja J. 2004. Comparison of late results of basic transsternal and extended transsternal thymectomies in the treatment of myasthenia gravis. Ann. Thorac. Surg. 78: 253-258.
Treatments on the horizon for MG
Christadoss P, Goluszko E. 2002. Treatment of experimental autoimmune myasthenia gravis with recombinant human tumor necrosis factor receptor Fc protein. J. Neuroimmunol. 122: 186-190.
Gangi E, Vasu C, Cheatem D, Prabhakar BS. 2005. IL-10-producing CD4+CD25+ regulatory T cells play a critical role in granulocyte-macrophage colony-stimulating factor-induced suppression of experimental autoimmune thyroiditis. J. Immunol. 174: 7006-7013. Full Text
Guo CY, Li ZY, Xu MQ, Yuan JM. 2005. Preparation of an immunoadsorbent coupled with a recombinant antigen to remove anti-acetylcholine receptor antibodies in abnormal serum. J. Immunol. Methods 303: 142-147.
Psaridi-Linardaki L, Trakas N, Mamalaki A, Tzartos SJ. 2005. Specific immunoadsorption of the autoantibodies from myasthenic patients using the extracellular domain of the human muscle acetylcholine receptor alpha-subunit. Development of an antigen-specific therapeutic strategy. J. Neuroimmunol. 159: 183-191.
Sheng JR, Li L, Ganesh BB, et al. 2006. Suppression of experimental autoimmune myasthenia gravis by granulocyte-macrophage colony-stimulating factor is associated with an expansion of FoxP3+ regulatory T cells. J. Immunol. 177: 5296-5306.
Zhu KY, Feferman T, Maiti PK, et al. 2006. Intravenous immunoglobulin suppresses experimental myasthenia gravis: immunological mechanisms. J. Neuroimmunol. 176: 187-197.
Organizers & Keynote
Henry J. Kaminski, MD
Henry J. Kaminski is chair of the Department of Neurology and Psychiatry at Saint Louis University. Until June 2007 he was vice chair and professor of neurology and professor of neurosciences at Case Western Reserve University. While there, he also served as chief of the Neurology Service at the Louis Stokes Cleveland VA Medical Center.
Kaminski is a nationally recognized expert in care of patients with myasthenia gravis and serves as secretary on the medical/scientific advisory board and is a member of the Committee for Clinical Research Standards at the Myasthenia Gravis Foundation of America. His research program, which has received continuous sponsorship by the National Institutes of Health since 1993, is working to understand of the biology of extraocular muscle and the pathogenesis of myasthenia gravis, in particular its preferential involvement of extraocular muscle. He has recently extended his work to development of complement inhibitor-based treatment of myasthenia gravis and muscular dystrophy.
Kaminski is a member of the executive committee of an NIH-sponsored trial to evaluate the role of thymectomy in management of patients with myasthenia gravis and is principal investigator of an ancillary study of biomarkers in myasthenia gravis.
Richard J. Barohn, MD
Richard Barohn is chair of the Department of Neurology at the University of Kansas Medical Center. He is the Gertrude and Dewey Ziegler Professor of Neurology. Among his research topics are myasthenia gravis, inflammatory myopathies, muscular dystrophy, motor neuron disease, and peripheral neuropathies. He has served on the editorial board for Neurology. He is currently chair of the Medical and Scientific Advisory Board of the Myasthenia Gravis Foundation of America, Inc. He also is chair of the Medical Advisory Committee for The Myositis Association. He was the founding chair and is now past chair of the Section of Neuromuscular Disease in the American Academy of Neurology.
Barohn completed a neurology residency at Wilford Hall USAF Medical Center and then a neuromuscular disease fellowship at Ohio State University. He started his academic career in the University of Texas system, first in San Antonio and then at University of Texas Southwestern in Dallas. At the University of Kansas Medical Center, he also serves as program director of the General Clinical Research Center and institute director for the Heartland Institute for Clinical and Translational Research.
Garry P. Nolan, PhD
Garry Nolan is an associate professor of genetics at the Stanford University School of Medicine. He leads a laboratory whose work focuses on signaling in the immune system and the host processes exploited by the HIV-1 virus. His lab is particularly interested in control of apoptosis, autoimmunity, angiogenesis, retrovirology, and blockade of HIV-1 infection. He has worked to develop methods of advanced flow cytometric analysis (FACS) of phosphoproteins in single cells and dominant effector genetics. He has developed a range of FACS assays, cDNA and peptide expression systems using viruses, and single-cell genetic selections to study pathways of interest.
Nolan completed his graduate studies at Stanford, where he studied with Leonard and Leonore Herzenberg. He later worked as a postdoctoral fellow in the laboratory of David Baltimore at MIT and the Rockefeller University.
Johan A. Aarli, MD
David Beeson, PhD
Sonia Berrih-Aknin, PhD
Jean-Pierre Changeux, PhD
Premkumar Christadoss, MD
Bianca Conti-Fine, MD
Judith A. Cossins, PhD
Gary Cutter, PhD
Marc De Baets, MD, PhD
Daniel Drachman, MD
Andrew G. Engel, MD
Amelia Evoli, MD
Sara Fuchs, PhD
Philippe Gajdos, MD
Henri-Jean Garchon, MD, PhD
Janet M. Golden
Chien-Ping Ko, PhD
Mark J. Kupersmith, MD
Bruno Kyewski, PhD
Daniel Lashley, MA, MBBChir, MRCP
Vanda A. Lennon, MD, PhD
Jon Lindstrom, PhD
Jie Luo, PhD
University of Pennsylvania Medical School
Renato Mantegazza, MD
Neurology IV, Neurological Institute "Carlo Besta"
Alexander Marx, MD
Ricardo A. Maselli, MD
Matthew N. Meriggioli, MD
John Newsom-Davis, MD
Robert M. Pascuzzi, MD
Jose M. Ponseti, MD, PhD, FACS
John D. Porter, PhD
Julie Rowin, MD
Jens C. Rückert, MD, PhD
Robert Ruff, MD
Donald Sanders, MD
Kazuhiro Shigemoto, MD, PhD
Joseph B. Shrager, MD
Steven M. Sine, PhD
Clarke Slater, PhD
Josh Sonett, MD
Jon Sussman, MD, PhD, FRCP
Russell Teichert, PhD
Socrates Tzartos, PhD
Steven Vernino, MD
Jan Verschuuren, MD, PhD
Angela Vincent, MD
Michael Werle, PhD
Nicholas Willcox, MD, PhD
Hugh J. Willison, MD, PhD
Gil Wolfe, MD
Lorne Zinman, MD
William Check is a science and medical writer based in Wilmette, IL.
Thank you to the following sponsors for their support.
David Beeson, University of Oxford
Judith Ann Cossins, University of Oxford
Daniel Lashley, University of Oxford
Ricardo A. Maselli, University of California at Davis
Garry Nolan, Stanford University
Many families with a hereditary form of MG have been described. Study of a large number of these kindreds has revealed a variety of genetic defects and a range of clinical profiles.
Genetic changes underlying CMS
Another discovery made since the 2003 conference, one equal in importance to the finding of MuSK MG, was the recognition of congenital myasthenic syndromes (CMS). This class of genetically based diseases is characterized by fatiguable muscle weakness caused by heterogeneous genetic defects.
Since the initial discovery of CMS, David Beeson and his colleagues at the University of Oxford have studied 189 CMS kinships, of which the vast majority have had a deficiency of AChR. Next most common was CMS with proximal weakness (limb girdle myasthenia) due to mutations in DOK7.
In many kindreds the defect in AChR was due to a mutation in RAPSN, the gene that codes for rapsyn, a protein that clusters and anchors AChR in the membrane of the muscle fiber of the NMJ. Clinically, CMS due to RAPSN defects results in life-threatening episodic respiratory crises precipitated by minor upper respiratory infection (URI).
To pursue the mechanism by which these gene defects cause CMS, the Oxford group devised an in vitro assay. By adding agrin, they induced myoblasts to differentiate into myotubes, and activated AChRs to cluster. They found that myoblasts from mice mutant in RAPSN still form AChR clusters, but the clusters are unstable. Beeson hypothesized that instability of clusters from RAPSN-mutant myoblasts might lead to vulnerability to fever-induced respiratory crises.
AChR clusters can also be induced in myotubes by adding Dok-7 instead of agrin. Mutations in DOK7 underlie CMS with proximal limb girdle muscle weakness, as described in an earlier talk by Slater. In this condition, there may be an initial response to AChEIs, but the condition later becomes unresponsive and deteriorates. It is frequently misdiagnosed.
Dok-7 binds to MuSK (muscle-specific receptor tyrosine kinase), accumulates at the NMJ, and colocalizes with AChRs. Both wild-type and mutant Dok-7 proteins bind MuSK. But in the myotube model Beeson's team found that AChR clusters induced by mutant Dok-7 are smaller than those induced by wild-type Dok-7 and are abnormally shaped. This could provide a clue to explain how CMS due to DOK7 mutations arises.
Using the same myotube model, Judith Ann Cossins of Oxford showed that plasma from myasthenia gravis patient with MuSK antibodies disrupts AChR clusters, This provides an additional tool for dissecting the pathogenic mechanism of MuSK antibodies.
DOK7 clinical case studies
Daniel Lashley of the Oxford group presented the clinical features of 18 patients with CMS due to DOK7 mutations. Most (72%) were diagnosed in the first three years of life. However, despite early problems (hypotonia, respiratory and bulbar weakness, ptosis, walking and postural difficulties), all had normal initial motor milestones. Subsequently they all developed mobility problems.
Common motor problems included eyelid ptosis, face/jaw weakness, tongue wasting, and neck weakness. All had limb weakness, with a proximal predominant (limb-girdle) weakness in two-thirds.
Consistent with other reports, efficacy of AChEIs was low: only one of 14 patients improved on pyridostigmine.
Ricardo A. Maselli of the University of California at Davis added descriptions of six cases of CMS due to DOK7 mutations. All patients had ptosis and proximal weakness; three required insertion of a gastrointestinal tube and two also needed mechanical ventilation.
Such cases are often misdiagnosed, Maselli said. Two patients' symptoms had been attributed to muscular dystrophy, another to Becker dystrophy, and a fourth to tracheomalacia. Once it became evident that these patients had congenital myasthenic syndrome, all were treated with pyridostigmine and three responded.
On muscle biopsy, post/presynaptic length was decreased by about half in the DOK7 patients. Postsynaptic clefts and folds decreased but the change was variable and "not dramatic," Maselli said. Electron microscopic abnormalities did not appear to correlate with the severity of symptoms. Maselli concluded that there is at this time no explanation for the clinical and pathogenic variation among these patients, even those with the same mutation.
Unraveling signaling networks with single-cell studies
In his keynote address Garry Nolan of Stanford University argued that "it's time to move beyond cell lines and mouse models" to patient samples. He described an approach to gaining information about signaling mechanisms from single cells using "barcoded" cells scanned by a flow cytometer.
Nolan "pokes and prods" immune system cells with signaling proteins like interferon (IFN) and interleukin (IL). He then uses antibodies to eight to ten intracellular molecules, including phosphorylated signaling proteins, to generate 2640 two-dimensional signaling plots or 5280 histograms, which are analyzed as arrays. With this technique, he is able to detect a change in response in a 1% subset of a cell population.
In a mouse model of systemic lupus erythematosus (SLE), this approach showed that CD4-positive cells lose their Stat 1 response to IL-6 over 5 to 20 weeks of disease progression. Real-time PCR analysis verified that loss of responsiveness was due to loss of gene activation.
Analysis of immune cells from human SLE patients showed broad suppression of responses to IFN-α. Moreover, unresponsiveness predicts disease score. Nolan called SLE "a disease of progressive unresponsiveness" that affects both T and B lymphocytes.
Nolan has also looked at cytokine responses of tumor cells from acute myelogenous leukemia patients. Increases in phosphorylation of Stat and other signaling molecules vary among patients. These patterns of internal phosphorylation can be used to characterize a negative prognosis group of patients.
Nolan also analyzed internal signaling responses of tumor-infiltrating immune cells in solid tumors. In one instance, the method showed a "massive" defect in signaling response in CD8-positive cells.
To add high-throughput capacity to flow cytometry, Nolan developed a method he calls "fluorescent cell barcoding" (FCB). In FCB, each sample is labeled with a different signature, or barcode, of fluorescence intensity and emission wavelengths, and mixed with other samples before antibody staining and analysis by flow cytometry. In FCB, results are obtained with much less reagent and more rapid turnaround time. This technique is ideal for drug screening.
Nolan predicted that these techniques would provide a form of personalized molecular medicine for determining the extent of progression of disease and of the efficacy of drug treatments. They could possibly offer insights into the roles of cytokines in MG as well.
Steven Vernino, University of Texas Southwestern Medical Center
Jan Verschuuren, Leiden University Medical Center
In this session, speakers provided insights into the pathogenesis of autoimmune autonomic neuropathy and the relationship of Lambert-Eaton myasthenic syndrome to small cell lung cancer.
Autoimmune autonomic neuropathy
The prototypic autoimmune disorder of synaptic transmission is myasthenia gravis, which features autoantibodies against muscle AChR. Acetylcholine is also an important neurotransmitter in both the central and peripheral nervous systems. Steven Vernino of the University of Texas Southwestern Medical Center discussed autoimmune conditions in which there are autoantibodies against ganglionic nicotinic AChR (nAChR).
Vernino and his colleagues have been studying a particularly dramatic form of dysautonomia that they call autoimmune autonomic neuropathy (AAN). AAN often has a subacute onset and leads to panautonomic failure, including both sympathetic failure (orthostatic hypotension and loss of sweating) and parasympathetic failure (dry eyes, dry mouth, bladder dysfunction, loss of heart rate regulation, and loss of pupillary light reflex). Patients often have prominent GI symptoms, typically gastroparesis, pseudoobstruction, or severe constipation.
Improvement in AAN has been seen in patients treated with either plasma exchange or intravenous immunoglobulin, suggesting an autoimmune basis. In 2000 Vernino's team found autoantibodies to ganglionic acetylcholine receptors in 19 of 46 (41%) patients with idiopathic or paraneoplastic autonomic neuropathy.
At this point Vernino and others had fulfilled two criteria that would establish AAN as an autoimmune disease: first, a relevant specific antibody had been identified in patients with the disease that binds in situ; second, it had been demonstrated that treatments to remove antibody are beneficial. More recently Vernino and his colleagues fulfilled criteria 3 and 4 by developing a rabbit model of experimental autoimmune autonomic ganglionopathy. Using active immunization with a subunit of ganglionic AChR they passively transferred the disease to mice using rabbit IgG containing antibodies against ganglionic AChR.
Remaining questions, Vernino said, include accounting for the 50% of patients with typical features of AAN but no antibodies, and establishing an effective therapy. He said that PLEX was "quite effective" in six patients in whom it was tried.
Relationship of Lambert-Eaton myasthenic syndrome to small cell lung cancer
Antibodies against the voltage-gated calcium channel (VGCC) cause Lambert-Eaton myasthenic syndrome (LEMS). To avoid confusing LEMS with classic MG, said Jan Verschuuren of Leiden University Medical Center, it is important to emphasize that there are only mild oculo-bulbar symptoms in LEMS, although these are accompanied with profound lower limb weakness.
An association between LEMS and small cell lung cancer (SCLC) has been known for many years: about half of LEMS patients eventually get a diagnosis of SCLC. In many cases diagnosis of the two conditions is simultaneous, but some SCLC cases are detected up to six months after diagnosis of LEMS. In 51 of 98 patients with LEMS diagnosed between 1990 and 2006, said Verschuuren, SCLC was found—92% within three months and 98% in one year.
Of significant clinical concern is how to detect lung tumors earlier in newly diagnosed LEMS patients. One indicator is smoking status: all 51 LEMS patients with SCLC had a positive smoking history; 86% were still smoking at diagnosis. Among the 47 LEMS patients who did not have SCLC diagnosed from 1.5 to 26 years after diagnosis, 71% were not smokers at diagnosis.
Patients with LEMS who do not develop SCLC are clinically indistinguishable from those who do. All develop proximal leg weakness within a year of LEMS diagnosis. Verschuuren evaluated 12 other symptoms. For the few symptoms that showed a difference between LEMS patients who did and did not develop SCLC (constipation, diplopia, dry mouth, impotence), symptoms developed sooner in tumor-related LEMS, implying more rapid disease progression for SCLC-associated LEMS.
Development of SCLC after a LEMS diagnosis is also more likely in individuals who are positive for anti-glial nuclear antibody (AGNA, identical with Sox-1).
In both English and Dutch cohorts, SCLC patients who also have LEMS live longer than those who don't; median survival is 24 vs. 7 months. This is not explained by lead time bias, said Verschuuren, since data were adjusted for stage of progression of SCLC. There is no correlation between presence of VGCC antibodies and survival; the presence of clinical signs and symptoms is necessary for survival advantage.
Study of a larger cohort should help to "refine the model for predicting SCLC in newly diagnosed LEMS patients," Verschuuren said.
Richard Barohn, University of Kansas Medical Center
Johan A. Aarli, University of Bergen, Norway
Donald Sanders, Duke University Medical Center
Robert Pascuzzi, Myasthenia Gravis Foundation of America
Lorne H. Zinman, Sunnybrook Health Sciences Center, Toronto, Canada
Philippe Gajdos, Hospital Raymond Poincaré, Paris, France
Over the decades since the discovery of MG, clinicians have brought a wide range of therapies to bear on this disease. Two traditional treatments—mycophenolate mofetil and IVIG—have recently been subjected to rigorous testing.
Progress in treatment and clinical research for MG
In his overview of treatment and clinical research in MG, Richard Barohn, of the University of Kansas Medical Center, noted that effective therapy started with physostigmine and neostigmine in the 1930s and progressed over the ensuing decades with the addition of thymectomy, mechanical ventilation, pyridostigmine, corticosteroids, and plasma exchange (PLEX). Azathioprine and cyclosporine were introduced in the 1970s and 1980s, followed by intravenous immunoglobulin (IVIG) and mycophenolate mofetil (MMF). With better management options, MG changed from being a "very grave" disease, with > 30% mortality before 1960, to < 5% mortality today. "We now expect most patients to improve and some to go into remission," Barohn said.
Published studies of treatments in MG have been mostly uncontrolled, nonrandomized and unblinded, Barohn said. He listed 13 randomized controlled trials (RCTs) performed since 1976, of which eight—all done since 1987—were positive.
MG is no longer a "very grave" disease, but results in < 5% mortality today.
For instance, reports in 1987 and 1993 showed that cyclosporine is more effective than placebo in both naive patients and steroid-dependent patients. In 1998 Jacqueline Palace and colleagues at the University of Oxford reported that azathioprine added to prednisolone produced a higher remission rate at 24 months and allowed a lower steroid dose than prednisolone plus placebo.
Many open trials with MMF got good results; however, three randomized clinical trials (RCTs) (also reported at this session) found no significant difference. Another trial to be reported at this session found a significant benefit with IVIG in acute exacerbation of MG. Barohn noted that the benefit has been called "modest" and that IVIG is very expensive—around $90,000 for a 2.0 gm/kg total dose.
Emerging therapies now being evaluated include EN101, an antisense ODN; etanercept, a TNF-α inhibitor; and high-dose cyclophosphamide. Some pioneering clinicians have also tried rituximab, a monoclonal antibody to B-cells, in difficult cases.
Barohn offered several reasons why RCTs in MG have shown no or only modest benefit, including the observation that MG is a difficult disease in which to measure improvement. Clinicians have noticed that it fluctuates in severity of its symptoms and some patients improve on placebo alone.
Barohn's therapy recommendations have changed somewhat as a result of new evidence. Mestinon, prednisone, and thymectomy remain first-line choices, with IVIG moved up to second line to join azathioprine and cyclosporine; MMF has dropped to his third line. Added in fourth and fifth place are newer investigational agents, including methotrexate, tacrolimus, rituximab, and cyclophosphamide. However, he stressed these are his personal treatment options, and physicians and patients need to make their own choices based on the available evidence.
MG in the elderly: is it different?
An important question for both therapeutic and clinical research is whether age influences presentation of MG. Johan A. Aarli of the University of Bergen pointed out that the threshold for "old" has risen over the past 25 years from 40 years of age to 50 years to 60.
One consideration of age is that typical MG symptoms—ptosis, diplopia, weakness of facial muscles—are easier to detect in younger persons, since aging brings on sagging of the lower eyelids, weakening of the small muscles around the eyes, and pouches under the eyes. "It may be difficult to identify ptosis in older persons," Aarli said.
Aarli looked at symptoms and antibodies to AChR, titin, and Ryanodine receptor (RyR) in 152 persons. He found that individuals who had either all three antibodies or anti-AChR and anti-titin were older at symptom onset (57 and 59 years) than those with only anti-AchR or no antibodies (35 and 38 years). In addition, a higher proportion of anti-RyR patients had marked non-limb pathology (ocular, bulbar, neck, or respiratory).
Myasthenia gravis has become more common in the elderly over time. In 1900 the average age at onset was 24 years for women and 35 for men, while in 1966 only 49% of female patients and 23% of males had onset of MG before the age of 30. Men had a second peak at 60–70 years. An increased incidence of elderly-onset MG patients was reported in 2005 in Nagano Prefecture, Japan. Aarli noted that this change in MG demographics has tracked with a more general increase in elderly persons in modern populations.
He concluded that MG in the elderly is basically the same disorder as in those with early onset of the disease. There is an additional immune response against other muscle proteins (titin, RyR) which is also seen in younger patients with thymoma and which may be tumor-related. "The combination of these factors contributes to the heterogeneity of the disease and makes myasthenia gravis in the elderly a special challenge to treatment and to research," Aarli said.
Trials of MMF for myasthenia gravis
Donald Sanders of Duke University Medical Center reported results on two trials of MMF in MG, one initiated by clinical researchers and one organized by Aspreva Pharmaceuticals.
Investigators in the first trial hypothesized that MMF with low-dose prednisone would be more effective than prednisone alone as initial immunotherapy for immunosuppression-naïve patients. In an initial blinded phase, 80 patients were treated for three months with 20 mg/day prednisone plus either 2.5 g/day MMF or placebo followed by a six-month open-label phase in which prednisone was tapered.
A study failed to demonstrate a difference between treatment with MMF and placebo.
No difference was seen in the primary outcome measure (mean decrease in QMG score at 12 weeks, ~30%) or in improvement in ADL. Nor did the extent of tapering of prednisone in the open-label phase differ (mean dose at 36 weeks). Sanders noted that there was a higher-than-expected response to prednisone alone and that patients had relatively mild disease at baseline (QMG, ~13).
Fewer details were available from the MMF trial sponsored by the pharmaceutical company. Sanders said that it used a unique steroid-sparing protocol designed to match clinical practice. In 176 patients at 43 international centers, prednisone was given at ≥ 20mg/day for ≥ 4 weeks, then MMF 2g/day or placebo was added for 36 weeks. After reaching minimal manifestations, prednisone was tapered to a target dose of 7.5mg/day.
This study also failed to demonstrate a difference between treatment with MMF and placebo, either in measures of signs and symptoms or in the ability to decrease steroid dose. In this trial, too, the benefit from steroids alone was greater than expected.
Following Sanders' talk, Robert Pascuzzi, president of the medical scientific board of the Myasthenia Gravis Foundation of America (MGFA), said that the board had decided to encourage a trial of MMF with a different protocol. The MGFA has agreed to fund a planning grant for an optimal protocol. Investigators are invited to submit proposals.
Trials of IVIG for myasthenia gravis
A 2004 review recommended IVIG as second-line therapy for MG but a 1997 RCT found no difference in efficacy between IVIG and PLEX, noted Lorne H. Zinman of Sunnybrook Health Sciences Center in Toronto. Zinman described an RCT of IVIG for exacerbation of MG that he and his colleagues carried out that had a positive outcome.
Zinman and colleagues randomized 50 MG patients with clinically apparent worsening of weakness to either 2.0 gm/kg of IVIG or an equivalent volume of D5W. Change in QMG at day 14 was significantly greater with IVIG and exceeded the clinically significant level of 3.5 units among more severe patients (baseline QMG > 10.5).
Effectiveness of IVIG for the treatment of moderate to severe MG exacerbations is established by two RCTs.
Philippe Gajdos of the Hospital Raymond Poincaré in Paris reviewed the data on the efficacy of IVIG for acute exacerbations of MG. Initially three uncontrolled open studies showed a benefit for IVIG. Subsequently four RCTs were performed, starting in 1997. One showed equivalence between IVIG and PLEX. Taking this study together with Zinman's work, Gajdos concluded that the effectiveness of IVIG for the treatment of moderate to severe MG exacerbations has been validated by two RCTs. He cautioned that few patients in true crisis were included in either trial and suggested that further trials are required to assess the efficacy of IVIG for treatment of MG crisis.
Matthew Meriggioli, University of Illinois Medical Center
Socrates Tzartos, Hellenic Pasteur Institute, Athens, Greece
Sara Fuchs, Weizmann Institute of Science
Jie Luo, University of Pennsylvania Medical School
Jon Lindstrom, University of Pennsylvania Medical School
Several investigators reported work in animal models of MG that could give rise to innovative, more effective therapies in the near future.
A number of experimental approaches to treating MG are being worked out in animal models, including the following:
- To target upstream steps in immune pathogenesis, Matthew Meriggioli of the University of Illinois Medical Center is generating ways to manipulate dendritic cells (DC), which are a type of antigen-presenting cells. Depending on their maturation status, DCs can also induce the production of regulatory T cells rather than effector T cells. One cytokine that promotes a Th2 response is GM-CSF. In an animal model, GM-CSF suppressed induction of EAMG while reducing levels of pro-inflammatory molecules and reducing mortality. Meriggioli suggested that GM-CSF may alter the balance between autoimmunity and tolerance, possibly acting through DCs.
- To make PLEX more selective, Socrates Tzartos of the Hellenic Pasteur Institute, Athens, is devising immunoadsorbent columns that carry recombinant human AChR fragments produced in either yeast or E. coli. Such columns have been shown to remove variable amounts of anti-AChR antibody from human MG serums. Depleted serum produces substantially less AChR antigenic modulation in cultured cells and does not induce EAMG.
- Treatment with IVIG ameliorates EAMG and MG. Perhaps only a subfraction of IVIG is needed to do this, reasoned Sara Fuchs of the Weizmann Institute of Science. She fractionated IVIG on an EAMG-specific column, one containing anti-AChR, anti-idiotype IgG. Specifically depleted material lost its ability to protect against EAMG. A similar effect occurred when IVIG was fractionated on a column containing IgG from MG patients. The therapeutic effect of IVIG is mediated by minute amounts of disease-specific anti-immunoglobulin activity, Fuchs concluded. Such anti-immunoglobulin activities can be isolated from IVIG and become preferential therapeutic reagents.
- Autoimmunity in MG is primarily directed against extracellular (EC) domains of AChR subunits. Jie Luo and Jon Lindstrom of the University of Pennsylvania Medical School made mixtures of fragments of AChR subunits and showed that, administered intraperitoneally, they suppressed induction of EAMG; using a mixture of only intracellular (cytoplasmic) domains proved equally effective as a mixture of EC and IC domains. Subunit mixtures diverted the autoimmune response from pathologically significant (EC) to insignificant (IC) epitopes. Such mixtures may provide a safer and more robust strategy for antigen-specific immunotherapy of MG, Luo and Lindstrom said.
What is the molecular basis of the 'size and shape' of the neuromuscular junction?
Genetic factors may account for only 10% of the risk of developing MG. What are the other risk factors and triggers?
Is there general inflammation in MG?
Is there a role for immunosuppressive drugs from other diseases, such as etanercept, in treating myasthenia gravis?
Can early prednisone therapy change the disease progression of MG?
What is the value of thymectomy? Is extensive resection superior?
What is the place of intravenous immunoglobulin in treating MG exacerbations? What is the optimal dose?
Is there a place for mycophenolate mofetil in treating MG?
How do antibodies to muscle-specific kinase cause disease? Should MuSK MG be treated differently? What are its disease triggers?
For the ~5% of MG patients lacking both anti-AChR and anti-MuSK antibodies, is there yet another antibody?
How can plasma cells that produce AChR antibody be eliminated?
Donald Sanders, Duke University
Gil Wolfe, University of Texas Southwestern Medical Center
Amelia Evoli, Catholic University, Rome
Angela Vincent, University of Oxford
Kazuhiro Shigemoto, Ehime University in Japan
Over the past several years several investigators contributed to the discovery and understanding of a new form of MG, one caused by antibodies to the muscle specific tyrosine kinase receptor (MuSK). Speakers provided detailed information about the clinical picture and therapeutic response of MuSK MG.
The clinical profile of MuSK MG
According to Donald Sanders of Duke University, the realization that myasthenia can be caused by antibodies to MuSK protein offers "an exciting new medical scenario." Considerable new information about this disease entity has come out since the 2003 MG conference, and at this year's event Gil Wolfe of the University of Texas Southwestern Medical Center described the clinical phenotype of MuSK antibody-positive MG based on his own work and that of several other teams of clinicians.
The first report of MuSK MG, which was published by the Oxford group in 2001, found antibodies against MuSK in 71% of seronegative generalized MG cases. Later studies by Wolfe and his colleagues and by other groups of investigators found a lower incidence; currently it is accepted that MuSK antibodies account for between 35% and 40% of cases of generalized MG that are negative for antibodies to the AChR, with a heavily female predominance. Ocular MG is less frequent in MuSK MG, but does occur.
When MuSK antibodies are present, MG is generally more severe and refractory to conventional therapy. For instance one study found significantly higher quantitative myasthenia gravis (QMG) scores at diagnosis in MuSK patients (12.9) than in MG patients with antibodies to the AChR (9.2). In another study, the MGFA severity class was higher in MuSK patients.
A severe oculobulbar pattern involving the face and tongue is most often seen in MuSK patients. Neck and shoulder muscles are affected and patients often have respiratory weakness. Relative ocular sparing is also common. A "classic" MG phenotype occurs as well.
Among 46 MuSK patients studied by Wolfe and other clinicians at eight U.S. centers, only 15% responded to AChE inhibitors (AChEI), much lower than with the anti-AChR type of MG, suggesting "an exaggerated cholinergic effect." About half of MuSK-antibody-positive patients had a response to corticosteroids and 37% to immunosuppressive agents. Efficacy for intravenous immunoglobulin (IVIG) was 19% and plasma exchange (PLEX) helped in 56% of cases. Overall, complete stable remission was achieved in 2% of patients and pharmacological remission in 15%.
Therapeutic response in MuSK MG patients
Amelia Evoli of Catholic University in Rome gave a detailed accounting of therapeutic response in MuSK MG patients. Evoli studied 57 patients, 79% of them women. Most patients had prevalent bulbar symptoms, with a high rate of respiratory crisis. "Myasthenia with anti-MuSK antibodies is often a severe disease requiring aggressive treatment," Evoli said.
In agreement with Wolfe's data, Evoli found the response to AChE inhibitors, including pyridostigmine, "generally unsatisfactory"—only about 20% of patients had a good response. She saw reduced tolerance to AChEI in MuSK-positive patients, with about a 10% risk of worsening symptoms, especially when starting treatment in patients with bulbar symptoms or impending respiratory crisis. She thus advised caution when initiating AChEI therapy in these patients.
Evoli also looked for clinical benefit in use of thymectomy and found no significant improvement. "It is controversial whether thymectomy has a role in treatment" of MuSK antibody-positive-MG, Evoli said.
Results show the need for caution when initiating AChEI therapy in MuSK MG patients.
In other cases, because of disease severity and poor response to AChEIs, 90%–100% of MuSK-positive patients require immunosuppression (IS). Treatment typically involves use of corticosteroids (generally prednisone) in conjunction with other drugs in intolerant or unresponsive patients, or as steroid-sparing agents. In published reports, Evoli and other clinical investigators have found that MuSK-positive MG responds less well to conventional immunosuppressive medications including prednisone, azathioprine (Azasan, Salix), and cyclosporine A (Sandimmum, Novartis). Evoli managed most of her patients with a combination of high-dose corticosteroids and cyclosporine or azathioprine. In a group of 13 refractory patients, good results were obtained with prednisone plus mycophenolate mofetil (MMF), high-dose cyclophosphamide (Cytoxan, Neosar) or, in a few patients, rituximab (Rituxan, Genentech and Biogen Idec).
In short-term therapy, MuSK MG responds as well to plasma exchange and intravenous immunoglobulin as standard MG. Most patients (58%) required at least one course of PLEX. In some cases, in spite of concomitant immunosuppression, the effect of PLEX tended to become shorter.
Even with optimal therapy, the remission rate in MuSK-antibody-positive MG is lower than in AChR-antibody-positive MG. Among Evoli's 57 MuSK MG patients, the response rate was 22%, significantly lower than the 39% rate in a large series of unselected MG cases. Only 18% of MuSK-positive patients have had complete withdrawal of therapy.
Finally, Evoli showed that a number of these patients developed permanent facial and bulbar weakness with facial and tongue atrophy, suggesting a myopathic process that could be related to the high-dose steroids or perhaps to MuSK antibody activity itself.
Observations on anti-MuSK and anti-AChR antibodies
Angela Vincent of the University of Oxford was one of the principal investigators in the initial discovery of MuSK MG. She gave an update on MuSK antibodies, which are found in about 40% of AChR-antibody-negative MG cases generally but in almost no cases of seronegative MG in Norway or Taiwan. Vincent showed that the variation in MuSK antibody prevalence is related to geography. In surveys done in Northern or Southern Europe, the United States, and Canada, prevalence ranges from zero at 60 degrees North to 40% at 20 degrees North. This pattern implies an environmental cause of the condition.
Proof that MuSK MG is truly an autoimmune disease (AID) has further illuminated the etiology of this condition. Persons working in this field have suspected that MuSK MG is an AID because an antibody of defined specificity was identified and because the condition responds to PLEX. Now Vincent and her coworkers, and Kazuhiro Shigemoto of Ehime University in Japan, have provided the final two pieces of evidence: active immunization with MuSK protein reproduces the disease in animals and passive transfer of human anti-MuSK antibodies produces defective transmission.
At the present time it is not clear how MuSK antibodies cause disease. In both human MuSK MG and a mouse model there is a definite neuromuscular transmission defect, yet the number of AChRs is not reduced and complement is not deposited at the NMJ. Early in vitro research suggests that MuSK antibodies may perturb intracellular pathways with downstream functional effects on AChRs and muscle, Vincent said, particularly atrophy-related genes. Consistent with this observation, MRI studies by Maria Elena Farrugia of the Oxford group showed that face and tongue muscles of MuSK MG patients have decreased volume and decreased force, consistent with muscle atrophy and fatty replacement.
Vincent next related work with MG patients who were apparently negative for both anti-AChR and anti-MuSK antibodies (seronegative MG, SNMG). Clinically and pathophysiologically, SNMG behaves like AChR MG, yet anti-AChR antibodies have not been found in these patients.
One possible hypothesis for this anomaly is that IgG antibodies to AChR are present in SNMG but that they bind weakly and get washed off during tissue preparation. To investigate this idea, Isabel Leite of the Oxford group studied binding of serum from SNMG patients in cultured cells in which AChRs were made to cluster using rapsyn. Under this condition binding to AChR was seen with serum from about half of SNMG patients, suggesting that at least some SNMG patients do have circulating anti-AChR antibodies.
Further work showed that SNMG antibodies are predominantly IgG1, like AChR-MG antibodies, and can activate complement, providing the beginnings of an explanation for SNMG disease.
Bruno Kyewski, German Cancer Research Center, Heidelberg
Henri-Jean Garchon, Inserm and the University Paris Descartes
Henry Kaminski,St. Louis University School of Medicine
Premkumar Christadoss, University of Texas Medical Branch, Galveston
Bianca Conti-Fine, University of Minnesota, Minneapolis
An up-to-date review sketched out our current understanding of how tolerance develops and how its breakdown might allow the rise of autoimmune diseases such as MG. In addition, data were presented of the important roles that complement and cytokines play in the development of MG and in experimental autoimmune myasthenia gravis.
A central role for central tolerance
All autoimmune diseases raise the question, Why is the immune system making antibodies to a self-antigen? Bruno Kyewski of the German Cancer Research Center, Heidelberg, addressed this conundrum, asking, How is self-tolerance to tissue-restricted antigens like AChR imposed and maintained?
To appreciate the magnitude of the task of imposing immunological tolerance, we can look at the basis of humoral immunity. As a consequence of random recombination among the V(D)J regions of Ig genes, an enormous number of antibody types is generated, creating a need for the body to screen antibodies against self-antigens. It is now accepted that this screening takes place in the thymus, with the key step being promiscuous expression of tissue-restricted self-antigens by medullary thymic epithelial cells (mTECs).
Self-antigen expression in mTECs mirrors virtually all tissues of the body, irrespective of developmental or spatiotemporal expression patterns. The pool of promiscuously expressed genes in mTECs might encompass up to 10% of the whole genome. Fetal antigens continue to be expressed postnatally (for example, α-fetoprotein and AChR-γ), which may preserve tolerance to fetal antigens. The bulk of promiscuous gene expression is in mature mTECs, which are short-lived and constantly renewed; the more these cells differentiate, the more genes they express.
To demonstrate unequivocally a link between specific thymic self-antigens and a single autoimmune phenotype, researchers at the University of California, San Francisco showed that lack of thymic expression of a single auto-antigen—interphotoreceptor retinoid-binding protein (IRBP)—can lead to a spontaneous organ-specific autoimmune syndrome in mice.
Two key findings help to explain expression of all self-antigens by mTECs: First, promiscuously expressed genes are highly clustered in the genome. Second, there is a specific transcription regulator, called the Autoimmune regulator gene (AIRE).
Kyewski and his colleagues showed that mTEC cells in thymic stroma don't mimic mammary gland cells: all mammary gland cells express all casein genes, while most mTEC cells express one or two. The complexity of regulation is further shown by the observation that AIRE expression is necessary but not sufficient for casein-α and -β expression. Other genes are regulated independently of AIRE.
The AIRE gene performs a critical function in autoimmune polyglandular syndrome-1 (APS-1), a rare autosomal recessive disorder characterized by immune-mediated destruction of endocrine tissues, chronic candidiasis, and additional ectodermal disorders (APECED). All are associated with AIRE mutations.
Autoimmune Polyglandular Syndrome-1 is associated with mutations of a single gene, Autoimmune regulator (AIRE).
Researchers from McGill University have provided evidence that genetic effects on tolerance influence the onset of insulin-dependent diabetes mellitus (IDDM, type 1), another autoimmune disease. Genetic susceptibility to IDDM is strongly influenced by the gene IDDM2, which is near the insulin gene and is located in a region of the chromosome that contains a stretch of variable number of tandem repeats (VNTR). The short class I VNTR alleles (26–63 repeats) predispose to IDDM, while class III alleles (140–210 repeats) have a dominant protective effect. The Canadian investigators showed that, in fetal thymus, a critical site for tolerance induction to self proteins, class III VNTR alleles are associated with two- to three-fold higher insulin mRNA levels than class I. To explain the dominant protective effect of class III VNTR alleles, the investigators proposed that higher levels of (pro)insulin in the thymus may promote negative selection of insulin-specific T-lymphocytes, which play a critical role in the pathogenesis of type 1 diabetes.
A similar situation exists in myasthenia gravis, which also features genetic control of central tolerance and a two- to three-fold difference in AChR gene expression between tolerance and disease. New data recently reported by Henri-Jean Garchon, of Inserm and the University Paris Descartes, along with Kyewski, Vincent, Beeson and others, show the effect of the promoter of the CHRNA1 gene on tolerance. A variant of the promoter of CHRNA1, the gene that encodes the alpha subunit of AChR, is associated with early onset of MG in populations in France and the United Kingdom. Both the CHRNA1 promoter variant and AIRE modulate production of CHRNA1 mRNA in mTECs, which could affect establishment of tolerance to AChR and allow earlier onset of MG.
Do extraocular muscles present a unique immunological environment?
The fact that extraocular muscles (EOM) are susceptible to MG demonstrates that autoimmunity can be regulated at the tissue level. According to Henry Kaminski of the St. Louis University School of Medicine, ocular symptoms are the first manifestation of MG in 50% of patients; 10% to 15% of patients show only ocular manifestations.
Why are EOM preferentially compromised by MG? Kaminski asked. The functional requirements of the ocular motor system by their vary nature lead to MG symptoms even when EOM pathology may be minimal. Also important, EOM comprise a unique immunological environment. Complement-mediated mechanisms are a critical part of the pathogenetic process in MG, and mRNA expression of complement regulators such as Decay Accelerating Factor (DAF) is seven-fold lower in EOM compared to other skeletal muscles.
Complement regulators such as Daf and CD59 are reduced by 60%–80% in EOM. Treatment of experimental autoimmune myasthenia gravis (EAMG) with a complement inhibitor (anti-C5) eliminates deposition of the complement component C9 at neuromuscular junctions in the thoracic diaphragm, but not at EOM junctions. Could low levels of complement inhibitors at EOM junctions put them at risk of injury at lower levels of AChR antibody?
Kaminski formulated what he calls the "complement hypothesis" to explain the particular susceptibility of extra-ocular muscles to MG. This hypothesis holds that intrinsic complement regulators are expressed at lower levels at EOM synapses, implying that complement inhibition does not prevent complement deposition at EOM junctions.
As support for this idea, Kaminski and others have shown "dramatic" protection and prevention of EAMG by infusion of a complement inhibitor, rEV576. It may now be moving into clinical trials.
Complement components are critical for development of EAMG
Premkumar Christadoss of the University of Texas Medical Branch, Galveston presented additional evidence of the importance of complement in the development and pathogenesis of EAMG. Christadoss and his colleagues performed an experiment using mice in which the genes for the complement components C3 and C4 had been eliminated, and showed them to be resistant to onset of EAMG after immunization with AChR. In both mutants, IgG deposits accumulated at the NMJ but C3 and other complement components did not.
Administration of antibodies that target the classical complement pathway component C1q also suppresses EAMG. When mice with EAMG were treated with anti-C1q, clinical severity was significantly reduced and lymph node cell IL-6 production was decreased. In addition, IL-6 deficient mice are resistant to EAMG, leading Christadoss to call IL-6 a "danger molecule."
In a pilot study, anti-IL-6 treatment also reduced the incidence and severity of EAMG and suppressed serum anti-AChR IgG antibody. Christadoss suggested that IL-6 blockade should be regarded as a potential therapy for MG.
Cytokines are important for development of EAMG
Bianca Conti-Fine of the University of Minnesota, Minneapolis has explored the importance of cytokines in the pathogenesis of acquired MG. In general, immune reaction depends on a balance of pro- and anti-inflammatory mediators. For instance, the Stat4 transcription factor promotes an inflammatory Th1 reaction, while Stat6 favors a modulatory Th2 reaction.
Mice deficient in IL-12/IL-23 expression are resistant to EAMG induction; mice deficient in Stat6 expression, on the other hand, are more susceptible to EAMG induction. These findings are consistent with the fact that IL-12 induces a Th1 response and Stat6 promotes Th2 cells. However, mice deficient in IFN-γ, which promotes Th1 cells, are more susceptible to EAMG, showing that the system is not straightforward.
In mice deficient in IL-4, which promotes a Th2 response, a single immunization with AChR leads to long-lasting muscle weakness, in contrast to EAMG in wild-type mice, which has limited duration even after three sensitizations. Conti-Fine suggested that IL-4 helps to downregulate development of an autoimmune response to the AChR.
To understand why mice lacking IFN-γ get EAMG, Conti-Fine created mice lacking IL-12/IL-23 and IFN-γ (dKO). These mutants have similar EAMG susceptibility to that seen in wild-type mice, which was somewhat surprising. In dKO mice, CD4 + CD25 + FoxP3 + T-regulatory (Treg) cells had less suppressive function. And dKO mice had as much pro-inflammatory IL-17 as wild-type mice. Conti-Fine speculated that the susceptibility of dKO mice to EAMG may be due to a combination of reduced Treg function and normal activity of pathogenic Th17 cells.
Clarke Slater, Newcastle University Medical School
Chien-Ping Ko, University of Southern California
Jean-Pierre Changeux, Institut Pasteur
Steven Sine, Mayo Clinic College of Medicine
Russell Teichert, University of Utah
While the basic facts about the structure of the NMJ have been known for some time, many investigators are elucidating important details about its function, including how nerve fibers trigger AChR activity.
Antibodies destroy NMJ structure
According to Clarke Slater of Newcastle University Medical School, "Myasthenia is basically a pathology of the NMJ." A NMJ is formed where a nerve terminal contacts a muscle fiber in a structure called a bouton, which has many ACh-containing vesicles. Where these vesicles abut the membrane they form active zones that release ACh quanta into the synaptic cleft during an action potential (AP); each bouton has 20 to 30 active zones.
Insight into how antibodies against the AChR bring about the symptoms of MG have come from comparative studies of the NMJ in different species. Slater showed that, although patterns of branching differ somewhat, the NMJ is largely similar across species. However, two major characteristics of the NMJ vary inversely among species: the number of ACh quanta released during an AP and the extent of postsynaptic membrane infolding. Quantal release is related to synaptic area—frogs have large synaptic area and high ACh quantal content, while human NMJs are very small and release few ACh quanta. To compensate for this, humans and other mammals rely on elaborate postsynaptic specializations to enhance the response to neurotransmitter.
In standard MG, destruction of the NMJ by antibodies to the AChR greatly reduces the efficacy of transmission. Last year (2006) investigators in Newcastle and Oxford identified a congenital myasthenic syndrome called limb girdel myasthenia (LGM), which primarily affects the proximal limb muscles. No antibodies to AChR were found in the LGM patients, but neuromuscular transmission was impaired.
Slater and the Oxford group studied a group of LGM patients and found that both quantal content and area of synaptic contact were approximately half those of control values. The extent of postsynaptic folding was also reduced by half. They concluded that impaired neuromuscular transmission in LGM patients results from reduced NMJ size and reduced postsynaptic folding. Interestingly, six of the seven patients that they studied have a defect in a gene called DOK7, which is necessary for formation of NMJ.
New findings in AChR signaling
Recent research has shown that formation and maintenance of the NMJ, as well as synapse formation, are strongly dependent on cells called perisynaptic Schwann cells (PSCs), which surround the NMJ. Chien-Ping Ko of the University of Southern California called the NMJ a tripartite synapse—nerve, muscle, and PSC. Death of PSCs leads to retraction of nerve terminals; conversely, PSC sprouting guides regeneration of nerve terminals. PSCs also promote synapse formation possibly through transforming growth factor beta 1 ((TGF-β1). In addition, PSCs express agrin and play a role in postsynaptic AChR aggregation.
Several investigators are seeking to understand how AChRs react to stimulation by the nerve fiber to trigger a response in muscle cells.
Nicotinic AChRs (nAChRs) are ion channels composed of an extracellular domain that carries the ligand-binding site and a distinct ion-pore domain. Signal transduction results from allosteric coupling between the two domains. Jean-Pierre Changeux of the Institut Pasteur investigated the functioning of the AChR using a method called normal mode analysis. Changeux found that coupling occurs through a global quaternary twist motion that opens the ion pore. Most mutations that cause congenital myasthenic syndromes (CMS) are located at residues that affect this gating mechanism. Changeux said that the work "provides a qualitative interpretation of the effect of pathological mutations responsible for CMS and suggests possible therapies using allosteric regulators of muscle nAChR."
Using single-channel recording, Steven Sine of the Mayo Clinic College of Medicine looked at how binding of ACh to the nAChR triggers the allosteric change in the receptor that opens the ion channel. He found three trigger sites that function sequentially, each composed of two to three amino acid residues. Mutation of any residue in the trigger structures interrupts the link between ACh binding and channel gating. Learning how the receptor moves when the ligand binds is a prerequisite to determining in molecular detail how mutations that cause CMS give rise to altered function, Sine said.
Russell Teichert of the University of Utah is taking another approach to investigating the function of AChRs. He uses toxins isolated from the cone snail, called conotoxins, and a toxin from Wagler's viper, called waglerin, to probe the expression and function of fetal vs. adult muscle nAChR subtypes. Fetal nAChR contains a gamma subunit, which during development is replaced by an epsilon subunit. One family of conotoxins selectively antagonizes fetal nAChR (one of these peptides has a 2000-fold affinity for the fetal subtype), while waglerin binds to the adult subtype.
These selective peptides allow basic studies in neuromuscular development and offer the potential for diagnostics and possibly drug targeting. "Additionally, conotoxins may have potential for direct clinical application," Teichert said.
Mark J. Kupersmith, Roosevelt Hospital
Julie Rowin, University of Illinois Medical Center
Jon Sussman, Greater Manchester Neuroscience Center, England
Joshua Sonett, Columbia University/New York Presbyterian Hospital
John Newsom-Davis, University of Oxford
Results with a broad range of therapies in MG were described. Several newer therapeutic candidates are now being evaluated in clinical trials.
Ocular myasthenia prednisone treatment trial
Acting on the hypothesis that ocular myasthenia (OM) is a forerunner of generalized MG (GMG), a group led by Mark J. Kupersmith of Roosevelt Hospital is testing whether prednisone therapy reduces the incidence of developing GMG at two years in patients presenting with OMG.
Is ocular myasthenia a forerunner of generalized MG?
The idea that OMG is a harbinger of GMG arises from the observations that ptosis or diplopia develop in 70%–84% of GMG patients and that within two years 50%–90% of OM generalizes. As a prelude to the prospective study, Kupersmith conducted a review of 94 OMG patients, 58 of whom were treated with prednisone and 36 of whom were not (treatment was not randomly assigned). Prednisone treatment reduced the odds ratio for having GMG at two years by 81%. (The only other predictor was the presence of anti-AChR, which increased the odds ratio by more than four-fold.) Only 7% of patients treated with steroids developed GMG at one year, compared to 36% of those treated only with AChEI.
In a trial under development, Kupersmith and investigators at a total of 40 clinical sites in the United States and Canada will treat OMG patients with moderate- to low-dose prednisone or placebo and the incidence of GMG at one year will be determined. The trial will also ask whether prednisone combined with pyridostigmine reduces ptosis and ocular motor dysfunction more than pyridostigmine alone. With 200 individuals in each arm, the trial will be powered to detect a 14% absolute (35% relative) reduction.
A trial of etanercept in MG
Julie Rowin and her colleagues at the University of Illinois Medical Center are leading a nine-center study of etanercept for therapy of MG. Etanercept (Enbrel, Amgen and Wyeth), a TNF-α blocker used extensively in rheumatoid arthritis (RA), is a soluble fusion protein of two TNF-α receptor molecules that binds to circulating TNF-α. In the experimental autoimmune myasthenia gravis model, Rowin and her colleagues found that etanercept suppressed established EAMG without influencing anti-AChR antibody.
These researchers then performed a pilot open-label trial of etanercept in 11 MG patients who remained symptomatic on ≥ 25 mg of prednisone administered every other day. Etanercept 25 mg was administered subcutaneously twice weekly for six months. Among the eight subjects who completed the trial, five improved by 3 or more points on the quantitative myasthenia gravis score (QMG). On average, prednisone dose was reduced by 20% among these eight subjects.
After reviewing published data on the safety profile of etanercept in RA, Rowin and colleagues concluded that there is no increased risk of serious adverse effects. They are recruiting 38 antibody-positive, steroid-dependent MG patients. Etanercept 50 mg or placebo will be given twice weekly subcutaneously for six months followed by a six-month open-label extension. The primary outcome measure will be the number of patients in each group who achieve a 30% reduction in prednisone dose at six months. The trial incorporates a forced steroid taper starting at four weeks for patients who are improved or stable.
Antisense therapy for MG
A more radical experimental molecule is being tested in a trial described by Jon Sussman of the Greater Manchester Neuroscience Center. Researchers had found that MG patients produce increased quantities of a variant of AChE that is made by alternative splicing of AChE pre-mRNA, termed the readthrough transcript (AChE-R). It exists in soluble form as opposed to the synaptic form of AChE, which is anchored in the postsynaptic membrane (AChE-S). It is thought that the soluble readthrough transcript may degrade the ACh before it crosses the synapse to the receptor.
Sussman and his colleagues synthesized a 20 base-pair antisense oligodeoxynucleotide called EN101/Monarsen that binds to the AChE transcript and promotes its cleavage. Monarsen binds to all AChE transcripts, but the readthrough transcript is longer and thus both less stable and more likely to be degraded. In the EAMG model, EN101 selectively lowered AChE-R levels while not affecting AChE-S levels. It improved survival, neuromuscular strength, and clinical status.
In a pilot trial in 16 patient with class II and III GMG, pyridostigmine was withdrawn on day 1 and EN101 titrated to 150 µg/kg. On three succeeding days, 500 µg/kg of EN101 was given. Pyridostigmine was resumed on day 6. Over the six days of the trial, 14 patients responded with an improvement in QMG score, with a mean improvement of about 50%. Improvement was noted after the second dose on day 1. Both vital capacity and swallowing time were improved. Cholinergic side effects were largely absent.
Encouraged by this result, Sussman and his colleagues at Ester Neuroscience and Hadassah University Hospital, Jerusalem, have begun a blinded comparative phase II study vs. pyridostigmine.
"Rebooting" the immune system in MG with high-dose cytoxan treatment
Another treatment that might be ready for a clinical trial is high-dose cyclophosphamide (Hi Cy) for patients with refractory MG. Daniel Drachman of Johns Hopkins School of Medicine calls this approach "rebooting" the immune system. Refractory MG is characterized by failure of response to adequate doses of conventional agents, unacceptable side effects, comorbidity precluding conventional therapy, or a requirement for repeated rescue with short-term treatment.
In animal experiments, Drachman initially tested "clean slate" therapy. He administered cyclophosphamide plus total body irradiation, followed by rescue using syngeneic bone marrow. After this treatment, rats reacted to an AChR booster just like naive animals. To determine whether total ablation with rescue is necessary, he also evaluated a less drastic procedure using Hi Cy. Mature white blood cells (WBCs) were eliminated, but bone marrow stem cells were not killed. Rapid reconstitution of the immune system followed, but it behaved differently.
Drachman and colleagues have used this protocol on many neurological autoimmune diseases (12 MG, 9 multiple sclerosis) and in > 100 patients with non-neurological autoimmune diseases (SLE, ITP, scleroderma). Since it is still experimental, they first get informed consent.
Following Hi Cy treatment the immune system reconstitutes itself, but behaves differently.
Of the 12 MG patients, 11 had severe disease (class IV or V); five had concomitant Hashimoto's or Graves' disease. Cyclophosphamide 50 mg/kg/day was given for four days, then six days later G-CSF was given. Patients are followed daily until hematologic recovery: when WBCs reach 1000/mm3, they go home. All subjects had nausea, hair loss, and anemia. (Among ~173 patients with autoimmune diseases treated this way, there have been three episodes of neutropenic sepsis and one intensive care admission; 40% got Herpes zoster [shingles]).
Six of the 12 MG patients had marked improvement for greater than one year; three others responded to drugs that hadn't worked before. One person followed for five months has also improved. Two had only short-term improvement. Drachman found that even patients who improve have a tendency to autoimmunity. He also pointed out that follow-up is necessary, because a rising anti-AChR titer can signal recurrence.
Even though all patients had been thymectomized, molecular tests showed recent thymic emigrants in the blood. It's not clear where they are coming from.
Hi Cy can dramatically help some patients with MG and its effect may be durable, Drachman concluded. However, patients must be carefully followed. He raised the possibility of trying it in patients who are not refractory. "It's not a terribly harsh treatment," he said.
Very early experience suggests that the monoclonal B-cell antibody rituximab may also be helpful in refractory MG. Clinicians from Germany and Oxford reported that one dose of rituximab ablated CD20-positive B cells and, along with conventional immunosuppression, induced clinical remission for up to four years in six patients, three each with anti-AChR and anti-MuSK antibodies. Rituximab "merits formal clinical investigation and may be considered at specialized centres in patients with severe [refractory GMG]," they concluded.
Thymectomy for MG
Joshua Sonett of Columbia University/New York Presbyterian Hospital addressed a number of questions about thymectomy for non-thymomatous MG. These included whether thymectomy is beneficial in MG, whether total thymectomy is important, and whether all procedures are equal. A lack of randomized controlled trials, along with variable patient selection in series that have been reported, have stymied resolution of this debate.
Reports that extended approaches create longer remissions led Sonett to conclude that complete surgical resection of thymus tissue in mediastinum is necessary.
However, such reports are based on retrospective review. To overcome this deficit, a randomized international single-blinded trial of thymectomy for AChR-positive MG sponsored by the National Institutes of Health is now being done. The accrual goal is 200 subjects. Study chair John Newsom-Davis of Oxford said that all patients will receive prednisone and will be randomized to transsternal thymectomy or not. Evaluators will be blinded. The primary outcome measures will be prednisone dose and QMG score at three years.
Myasthenia gravis (MG) is a neuromuscular disease characterized by fluctuating muscle weakness with fatigability. This weakness chiefly affects the oculofacial muscles and the proximal skeletal muscles. MG is marked by exacerbations and remission, and some patients experience severe, life-threatening weakness that can require intubation with mechanical ventilation.
A Virginia settler's 1622 description of a Native American chieftan, Opechancanough, is one document of the ocular manifestation of myasthenia gravis, which includes drooping of the eyelids, called ptosis: "[H]is eyelids were too heavy that he could not see unless they were lifted up by his attendants." Several modern descriptions of MG were published in the late 19th century, and since the mid-20th century doctors have understood that symptoms are caused by miscommunication between nerve and muscle.
Many researchers favored the hypothesis that MG is an autoimmune disease, since MG often co-existed with other disorders that were thought to be autoimmune in nature. But it was not until the 1970s that the breakthrough occurred that revealed the pathogenetic basis of this condition: myasthenia gravis is caused primarily by an autoimmune reaction against the acetylcholine receptor (AChR) that destroys the integrity of the neuromuscular junction (NMJ) and disrupts neuromuscular transmission. It was a serendipitous finding—while making antibodies to AChR in rabbits, Jim Patrick and Jon Lindstrom observed that the animals developed a disease identical to myasthenia. Five years later John Newsom-Davis used plasmapheresis to show that disease severity was decreased in humans when correlated with a drop in titer of antibodies to the AChR.
Myasthenia gravis is among the best understood autoimmune diseases and is one of the only ones that fulfills strict criteria for autoimmunity.
Myasthenia gravis is among the best understood autoimmune diseases and is one of the only ones—if not the only one—that fulfills strict criteria for autoimmunity: a known antibody, the ability to induce the disease in animals with the primary antigen, passive transfer with serum, and alleviation of manifestations by removing antibody. Because of its well-understood biochemical and physiologic mechanism, MG has been studied to a greater extent than would be predicted from its low incidence—two to four cases per million, with a prevalence of 400 per million. Although MG is so rare that is has "orphan disease" status, it serves as a model for other autoimmune diseases such as immune thrombocytopenic purpura (ITP). And because it is a disease of the NMJ, the simplest synapse, it is used as an analogy for synapse function in the brain in conditions such as epilepsy.
Since 1954 the New York Academy of Sciences has been cosponsoring international conferences on MG as a way for researchers in this field to stay current with new developments and to exchange ideas. The meetings are valuable to clinicians. "These conferences and publications are a position paper on the status of knowledge in this area," said Robert Pascuzzi, president of the medical scientific board of the Myasthenia Gravis Foundation of America (MGFA), in his introduction to the most recent conference, held in Chicago in May 2007. "They occupy center stage for dissemination" of the newest ideas to practitioners.
In addition to this eBriefing, the New York Academy of Sciences will also be publishing a forthcoming volume of the Annals of the New York Academy of Sciences, dedicated to myasthenia gravis.
At the 2007 meeting researchers presented findings on a broad range of basic and clinical topics. This was a particularly dynamic conference, since many important advances have been made in the last several years regarding both pathogenesis and therapy.
Research highlights of the conference included the following:
Structure and function of the NMJ and of the AChR
Scientists have achieved a better understanding of the NMJ and how its structure and function are disrupted in MG, and in particular of the role of perisynaptic Schwann cells in forming and maintaining the NMJ. In addition, studies have revealed conformational information about the function of the AChR as an ion channel and how its function is altered by mutations.
Muscle-Specific Kinase (MuSK) and MG
In 10%–15% of MG patients no antibodies to the AChR can be detected. In the last few years researchers have established that many of these cases are caused by a novel autoantibody to a protein component of the NMJ: muscle specific kinase (MuSK). "These results strongly support previous studies suggesting that seronegative myasthenia gravis should be considered a distinct subtype of myasthenia," said conference cochair Henry Kaminski of St. Louis University. At the conference researchers described clinical features of MuSK MG along with possible disease mechanisms, which are distinct from standard MG. Many individuals with MuSK MG develop atrophy of muscles, which doesn't occur in standard MG. Patients with MuSK MG also respond differently to therapy than persons with standard MG.
Congenital myasthenic syndromes (CMS)
For many years familial clustering of MG has been observed in a small proportion of cases. Genetic analysis has now uncovered specific mutations that are most commonly found in CMS and ideas about how they may interfere with the structure of the NMJ, such as preventing effective integration of AChRs into membranes.
Autoimmune pathogenesis of MG
In MG, as in all autoimmune diseases, a major question is why the immune system produces antibodies against self components. The conference featured recent findings about how tolerance is induced in the thymus, along with ideas about how tolerance may be broken in MG. Work on experimental models of MG has shown the critical pathogenic role of complement in destruction of the NMJ and the dual roles of cytokines in promoting and blocking immunological activity against the AChR.
Current and future treatments for MG
The third day of the conference was devoted to therapeutic topics, including standard therapies that are being looked at more closely. For instance, said conference cochair Richard Barohn of the University of Kansas, "Thymectomy is still a controversial area. We aren't sure that it shows benefit." This despite the fact that procedures for removing the thymus gland have been performed in MG patients since the early 1900s. The conference offered an opportunity to review the status of an ongoing NIH-sponsored randomized international study of thymectomy in MG patients. "There is a major push underway to evaluate these older therapies rigorously," Kaminski agreed.
"This trial of antisense in MG patients appears to be the first successful one in humans."
Many promising and exciting new therapeutic options are also being evaluated, including an antisense oligodeoxynucleotide (ODN). "This trial of antisense in MG patients may be the first successful one in humans," Kaminski said. "It is truly unique and of general scientific interest. It represents rapid translation of a unique biological observation into clinical application."
Highlights of the clinical sessions included the following:
Completed clinical trials of traditional therapies
Many modalities used to treat MG have simply been borrowed from other autoimmune disorders without evidence that they are effective in MG. Results from trials evaluating two of these—intravenous immune globulin (IVIG) and mycophenolate mofetil (MMF)—were presented, showing that IVIG is effective in treating exacerbations but that MMF appears not to be effective as adjunctive therapy to prednisone.
Ongoing clinical trials of existing therapies
Other treatments already in clinical use are in the midst of evaluation. In addition to the randomized international trial of thymectomy, a multicenter study of the tumor necrosis factor-alpha (TNF-α) blocker etanercept (Enbrel, Amgen and Wyeth) is under development. Etanercept is in widespread use against rheumatoid arthritis and showed promise in a pilot trial in MG.
Many MG patients present initially with ocular symptoms. Ocular myasthenia (OM) may be a harbinger of generalized MG. To test this idea, a group of investigators has set up a trial to determine whether early prednisone therapy in patients with OM reduces the incidence of generalized disease.
Treatments on the horizon
A few years ago it was found that MG patients produce a rapid-acting variant of acetylcholinesterase (AChE), the enzyme that degrades acetylcholine. The antisense oligodeoxynucleotide EN101 (Monarsen) preferentially promotes degradation of this destructive variant of AChE, thereby enhancing ACh action at the NMJ. After showing benefit in an open-label study, EN101 is now being evaluated in a randomized controlled trial.
At one center an intensive regimen of high-dose cyclophosphamide has been used for several years to treat refractory MG patients. Results with this regimen to date were reviewed.
Work in animal models was described that suggests the potential utility of several still-experimental therapies: manipulation of the ability of dendritic cells to stimulate immune reactivity against AChRs; specific apheresis to remove antiAChR antibodies; complement inhibition; isolation of the specific immunosuppressive fraction of IVIG; and administration of a mixture of the subunits that comprise the AChR to alter immune reactivity.
Taken together, these talks provided a comprehensive overview of contemporary pathogenetic and therapeutic research into myasthenia gravis.
William Check is a science and medical writer based in Wilmette, IL.