Liewluck T, Selcen D, Engel AG. Beneficial effects of albuterol in congenital endplate acetylcholinesterase deficiency and Dok-7 myasthenia. Muscle Nerve. 2011 Nov;44(5):789-94.
Congenital myasthenic syndromes (CMS) are disabling but treatable disorders. Anticholinesterase therapy is effective in most of them, but is contraindicated in endplate (EP) acetylcholinesterase (AChE) deficiency, the slow-channel syndrome, Dok-7 myasthenia, and β(2) -laminin deficiency, and is not useful in CMS due to defects in muscle-specific kinase (MuSK), agrin, and plectin. EP AChE, Dok-7, and β(2)-laminin deficiencies respond favorably to ephedrine, but ephedrine can no longer be prescribed in the USA.
We used albuterol, another sympathomimetic agent, to treat 3 patients with EP AChE deficiency and 15 with Dok-7 myasthenia. Response to therapy was evaluated by a 9-point questionnaire pertaining to activities of daily life.
Comparison of the pre- and posttreatment responses indicated a beneficial response to albuterol (P < 0.001) in both patient groups. The adverse effects of therapy were like those of ephedrine.
Our observations should spur controlled, prospective clinical trials of albuterol in these as well as other CMS.
Farmakidis C, Pasnoor M, Barohn RJ, Dimachkie MM. Congenital Myasthenic Syndromes: a Clinical and Treatment Approach. Curr Treat Options Neurol. 2018 Jul 21;20(9):36.
PURPOSE OF REVIEW:
Congenital myasthenia syndromes are clinically and genetically heterogeneous but treatable conditions. Careful selection of drug therapy is paramount as the same drug can be effective, ineffective, and even harmful in different congenital myasthenia syndromes. The purpose of this article is to review current treatment options for these conditions.
Next-generation sequencing has accelerated the discovery of new genes and facilitated the description of novel congenital myasthenic syndromes. Retrospective therapy data from these newly identified syndromes has provided additional insight on the management of these conditions. Cholinergic agents, β-adrenergic agonists, and open-channel blockers remain the principal treatment modalities, and their optimal use depends on an accurate genetic diagnosis and the timely clinical recognition of the disease. In particular, pyridostigmine, usually a first-line agent, should be avoided in DOK7, acetylcholinesterase deficiency, and slow-channel congenital myasthenic syndromes. Beta-adrenergic agonists have been recognized as a first-line agent for a number of congenital myasthenic syndromes, particularly DOK7 and acetylcholinesterase deficiency, whereas long-lived open-channel blockers of the acetylcholine receptor (AChR) ion channel are indicated for the slow-channel congenital myasthenic syndrome. Beta-adrenergic agonists additionally have an important adjunct treatment for congenital myasthenia syndrome due to glycosylation defects, fast channel syndrome, AChR deficiency, and choline acetyltransferase deficiency (ChaT) and therefore may be particularly important in the treatment of syndromes due to defects in motor endplate development and repair. Unlike in autoimmune myasthenia gravis, there is no role for immunotherapy in congenital myasthenic syndromes. If available, a genetic diagnosis should drive the choice for a first-line treatment agent between cholinergic agents, β-adrenergic agents, and open-channel blockers. Evaluation and supportive care at centers with experience in these rare syndromes likely are paramount in achieving optimal outcomes. Furthermore, gene discovery for congenital myasthenic syndromes has provided novel insights on the role of protein glycosylation, endplate maintenance and repair, and synaptic vesicle exocytosis in neuromuscular transmission. These insights may lead to new therapeutic strategies in both congenital and autoimmune myasthenic diseases in the future.
Evoli A, Alboini PE, Damato V, Iorio R, Provenzano C, Bartoccioni E, Marino M. Myasthenia gravis with antibodies to MuSK: an update. Ann N Y Acad Sci. 2018 Jan;1412(1):82-89.
Myasthenia gravis with antibodies to the muscle-specific tyrosine kinase (MuSK+ MG) is a rare disease with distinctive pathogenic mechanisms and clinical features. An acute onset and predominant bulbar muscle weakness are very common and highly suggestive of the disease. On the other hand, a more indolent course, atypical ocular presentation, and signs of cholinergic hyperactivity may complicate the diagnosis. Though MuSK+ MG is still a severe disease, over the years we have observed a steady reduction in the rate of respiratory crisis and a significant improvement in the clinical outcome, both likely related to earlier diagnosis and timely treatment. Despite the improved management, MuSK+ MG patients tend to remain dependent on long-term immunosuppressive treatment and may develop permanent disabling weakness. In uncontrolled studies, B cell depletion with rituximab proved effective in most patients with refractory disease, inducing prolonged clinical responses associated with a sustained reduction of serum antibody levels. Promising results from experimental studies and case reports suggest that both 3,4-diaminopyridine and albuterol may be effective as symptomatic agents.
Ghazanfari N, Morsch M, Tse N, Reddel SW, Phillips WD. Effects of the ß2-adrenoceptor agonist, albuterol, in a mouse model of anti-MuSK myasthenia gravis. PLoS One. 2014 Feb 5;9(2):e87840. doi: 10.1371/journal.pone.0087840.
The β2-adrenergic receptor agonist, albuterol, has been reported beneficial in treating several forms of congenital myasthenia. Here, for the first time, we examined the potential benefit of albuterol in a mouse model of anti-Muscle Specific Kinase (MuSK) myasthenia gravis. Mice received 15 daily injections of IgG from anti-MuSK positive patients, which resulted in whole-body weakness. At neuromuscular junctions in the tibialis anterior and diaphragm muscles the autoantibodies caused loss of postsynaptic acetylcholine receptors, and reduced the amplitudes of the endplate potential and spontaneous miniature endplate potential in the diaphragm muscle. Treatment with albuterol (8 mg/kg/day) during the two-week anti-MuSK injection series reduced the degree of weakness and weight loss, compared to vehicle-treated mice. However, the compound muscle action potential recorded from the gastrocnemius muscle displayed a decremental response in anti-MuSK-injected mice whether treated with albuterol or vehicle. Ongoing albuterol treatment did not increase endplate potential amplitudes compared to vehicle-treated mice nor did it prevent the loss of acetylcholine receptors from motor endplates. On the other hand, albuterol treatment significantly reduced the degree of fragmentation of endplate acetylcholine receptor clusters and increased the extent to which the remaining receptor clusters were covered by synaptophysin-stained nerve terminals. The results provide the first evidence that short-term albuterol treatment can ameliorate weakness in a robust mouse model of anti-MuSK myasthenia gravis. The results also demonstrate that it is possible for albuterol treatment to reduce whole-body weakness without necessarily reversing myasthenic impairment to the structure and function of the neuromuscular junction.