Acetylcholine receptor antibodies in patients with genetic myopathies: clinical and biological significance

AChR-seropositive myasthenia gravis in muscular dystrophy: diagnostic pitfalls and clinical management challenges

The co-occurrence of genetic myopathies with myasthenia gravis (MG) is extremely rare, however a few studies have been reported. We aim to explore the link between genetically inherited muscle disorders and immune-mediated neuromuscular junction conditions, taking into account the diagnostic and therapeutic implications posed by these combined conditions. We searched all English medical papers registered in Web of Knowledge, PubMed, Google Scholar, and Science Direct between January 1987 concerning the association between muscular dystrophies (MD) and MG, also adding three new cases to the series reported so far. Three new clinical cases in which MG concurs with oculopharyngeal muscular dystrophy (OPMD) or facioscapulohumeral muscular dystrophy (FSHD) or myotonic dystrophy type 2 (DM2) were reported. A comprehensive literature review showed that FSHD is the dystrophy most frequently associated with generalized MG. The AChR antibody titer is high and neurophysiologic tests prove to be an essential tool for the diagnosis. The association between MG and MD is rare but should not be underestimated. The presence of unusual clinical features suggest investigating additional overlapping condition, especially when a treatable disease like MG is suspected.

Oculopharyngeal muscular dystrophy, myasthenia gravis, systemic lupus erythematosus: overlap and interactions

Ptosis and proximal weakness may develop in multiple diseases including oculopharyngeal muscular dystrophy (OPMD) and myasthenia gravis (MG). These two entities can be challenging to differentiate since they may have important clinical and neurophysiological overlap. Systemic lupus erythematosus (SLE), a common autoimmune disease, has been described in association with MG.We present a woman in her 60s with fluctuating bilateral ptosis and proximal muscle weakness. Single fibre electromyography showed increased jitter. Her brother has genetically proven OPMD. The investigation revealed a positive genetic test for OPMD and positive antibodies for acetylcholine receptor. Additionally, she has SLE, treated with hydroxychloroquine for more than 30 years.This case highlights the importance of a thoughtful anamnesis with personal and familial history and raises awareness for the rare coexistence of three pathologies with some common clinical characteristics but different treatments and management.

Oculopharyngeal muscular dystrophy coexisting with myasthenia gravis

Oculopharyngeal muscular dystrophy (OPMD) and myasthenia gravis are both rare conditions of different pathophysiological nature, so a fortuitous association is unlikely. However, antiacetylcholine receptor antibodies may be found in other genetic myopathies and this is probably not coincidental. Muscle fibre degeneration can induce innate immune responses that may break immune tolerance and allow the generation of autoantibodies to muscle proteins. We report a patient with atypical OPMD who also had acetylcholine receptor antibody-mediated myasthenia gravis. This report raises awareness of the diagnostic and treatment implications of the association of myasthenia gravis with genetic myopathies.

c.3G>A mutation in the CRYAB gene that causes fatal infantile hypertonic myofibrillar myopathy in the Chinese population

Infantile hypertonic myofibrillar myopathy is characterized by the rapid development of rigid muscles and respiratory insufficiency soon after birth, with very high mortality. It is extremely rare, and only a few cases having been reported until now. Here we report four Chinese infants with fatal neuromuscular disorders characterized by abdominal and trunk skeletal muscle stiffness and rapid respiratory insufficiency progression. Electromyograms showed increased insertion activities and profuse fibrillation potentials with complex repetitive discharges. Immunohistochemistry staining of muscle biopsies showed accumulations of desmin in the myocytes. Powdery Z-bands with dense granules across sarcomeres were observed in muscle fibers using electron microscopy. All patients carry a homozygous c.3G>A mutation in the CRYAB gene, which resulted in the loss of the initiating methionine and the absence of protein. This study's findings help further understand the disease and highlight a founder mutation in the Chinese population.

Congenital myasthenic syndrome with novel pathogenic variants in the COLQ gene associated with the presence of antibodies to acetylcholine receptors

Congenital myasthenic syndrome (CMS) is a heterogeneous group of inherited disorder which does not associate with anti-acetylcholine receptor (AChR) antibody. The presence of AChR autoantibody is pathogenic and highly sensitive and specific for autoimmune myasthenia gravis (MG). We describe 2 children from unrelated families who presented with hypotonia, ptosis and fatigability in early infancy with anti-AChR antibodies detected via ELISA on 2 separate occasions in the sera. Both were treated as refractory autoimmune MG due to poor clinical response to acetylcholinesterase inhibitor and immunotherapy. In view of the atypical clinical features, genetic studies of CMS were performed and both were confirmed to have novel pathogenic mutations in the COLQ gene. To the best of our knowledge, the presence of anti-AChR antibody in COLQ-related CMS has never been reported in the literature. The clinical presentation of early onset phenotype, and refractoriness to acetylcholinesterase inhibitor and immunotherapy should prompt CMS as a differential diagnosis.

The development of myasthenia gravis in a patient with facioscapulohumeral muscular dystrophy: case report and literature review

The co-existence of facioscapulohumeral muscle dystrophy (FSHD) and myasthenia gravis (MG) is very rare and few cases have been described in the literature. To increase the awareness of the health care providers, we present herein a rare case of MG in a patient with FSHD, discuss the diagnostic challenges, pre- and post-treatment findings and provide a literature review.

How common is childhood myasthenia? The UK incidence and prevalence of autoimmune and congenital myasthenia

OBJECTIVE

To ascertain the frequency of childhood myasthenia in the UK. Specifically, we aimed to identify the detected incidence of autoimmune myasthenia and the detected prevalence of genetically confirmed congenital myasthenic syndrome (CMS) in children.

METHODS

All children under 18 years of age on 31 December 2009 with a confirmed CMS genetic mutation were identified by the only UK laboratory undertaking CMS genetic testing. All cases with positive acetylcholine receptor (AChR) and muscle specific kinase (MuSK) receptor antibodies in the 5 years between 2003 and 2007 inclusive were identified by the testing laboratories. UK census data from 2001 were used as the denominator for analyses.

RESULTS

The UK detected prevalence of genetically confirmed CMS was 9.2 per million children under 18 years of age. CMS was equally prevalent in girls and boys. CHRNE, RAPSN and DOK7 were the most commonly identified mutations. Prevalence varied across geographical regions in England (between 2.8 and 14.8 per million children). The mean incidence of antibody-positive autoimmune myasthenia was 1.5 per million children per year over the period of the study. Girls were affected more frequently than boys; this difference persisted across the age range. Antibodies were identified during the neonatal period in 17 children.

CONCLUSIONS

This laboratory based study shows that childhood myasthenia is very rare. This condition is treatable, and these definitive detected incidence and prevalence data can be used to help plan diagnostic and supporting services for affected children and their families, and maximise research opportunities.

Oculopharyngeal muscular dystrophy as a cause of progression of weakness in antibody positive myasthenia gravis

Many neuromuscular conditions cause bulbar and limb weakness, and when several conditions coexist they present additional diagnostic challenges. Here we describe a case of a 45-year-old woman with antibody positive myasthenia gravis since age 16, who then develops treatment-resistant weakness due to genetically proven oculopharyngeal muscular dystrophy. We conclude that the development of treatment-resistant weakness in myasthenia gravis should spur further work up for other neuromuscular disorders including oculopharyngeal muscular dystrophy.

A Case Report of Congenital Fiber Type Disproportion with an Increased Level of Anti-ACh Receptor Antibodies

Congenital fiber type disproportion (CFTD) is a form of congenital myopathy, which is defined by type 1 myofibers that are 12% smaller than type 2 myofibers, as well as a general predominance of type 1 myofibers. Conversely, myasthenia gravis (MG) is an acquired immune-mediated disease, in which the acetylcholine receptor (AChR) of the neuromuscular junction is blocked by antibodies. Thus, the anti-AChR antibody is nearly specific to MG. Herein, we report on a case of CFTD with increased anti-AChR antibody levels. A 23-month-old boy exhibited muscle hypotonia and weakness. Although he could walk by himself, he easily fell down and could not control his head for a long time. His blood test was positive for the anti-AChR antibody, while a muscle biopsy revealed characteristics of CFTD. We could not explain the relationship between MG and CFTD. However, we considered different diagnoses aside from MG, even when the patient's blood is positive for the anti-AChR antibody.