Fetal acetylcholine receptor inactivation syndrome: A myopathy due to maternal antibodies

Risk of False Acetylcholine Receptor Autoantibody Positivity by Radioimmunoprecipitation Assay in Clinical Practice

BACKGROUND AND OBJECTIVES

Radioimmunoprecipitation assay (RIPA) is the gold standard for acetylcholine receptor (AChR)-immunoglobulin G (IgG) detection in patients with myasthenia gravis (MG), with a reported specificity of ≈99%. The risk of "false" AChR-IgG positivity in clinical practice is often considered negligible, although data on large, real-life populations are scarce. The objective of this study was to determine the positive predictive value (PPV) and risk of false AChR-IgG positivity with RIPA in a large cohort of patients with suspected MG.

METHODS

We retrospectively identified patients consecutively tested for AChR-IgG by RIPA at the University-Hospital of Sassari over 20 years (2003-2022) (n = 4,795). Medical records of AChR-IgG-positive patients (titer ≥0.5 nmol/L) were reviewed by 2 investigators to identify nonmyasthenic cases with false antibody positivity, defined as follows: (1) clinical phenotypes not consistent with MG and/or (2) symptoms better explained by alternative diagnoses. The characteristics of myasthenic and nonmyasthenic patients with AChR-IgG positivity were compared. A sample of nonmyasthenic patients was retested by fixed cell-based assay (CBA).

RESULTS

Among 445 of 4,795 patients testing positive for AChR-IgG during the study period, 83 were excluded (insufficient information). Of 362 AChR-IgG-positive patients included, 50 (13.8%) were designated as nonmyasthenic. The PPV and specificity were 86.2% (95% CI 82.2-89.6) and 98.9% (95% CI 98.5-99.2), respectively. Alternative diagnoses in nonmyasthenic patients included ophthalmologic diseases (n = 8), rheumatic diseases (n = 7), pseudoptosis (n = 5), myopathy (n = 4), functional disorders (n = 3), cranial nerve palsy (n = 2), parkinsonism (n = 2), demyelinating diseases (n = 2), and others (n = 17). Compared with patients with MG, nonmyasthenic patients were younger (median age 65 [range 7-91] vs 38 [range 5-80] years), more frequently female (155/312 [49.8%] vs 37/50 [74%]), had lower AChR-IgG titers (median 6 [range 0.5-28] vs 0.7 [range 0.5-5.5] nmol/L), and were more likely to become seronegative on subsequent tests (9/120 [8%] vs 6/11 [55%]). After stratification by titer ≥1 nmol/L, the PPV increased to 96.6% (95% CI 94-98.3). Serum of 7 nonmyasthenic patients was retested by CBA, giving negative results (n = 6) or selective positivity against the fetal AChR isoform (n = 1).

DISCUSSION

False AChR-IgG positivity may occur in clinical practice with RIPA and associates with low antibody titer. Caution is needed when titers between 0.5 and 0.9 nmol/L are detected in low-probability situations because failure to recognize false antibody positivity may lead to misdiagnosis and inappropriate treatments.

Surface-enhanced Raman scattering probes based on sea urchin-like Bi2S3@Co3O4 composite for the detection of dopamine during neural stem cell differentiation

Dopamine (DA) is a significant neurotransmitter involved in various functions of the central nervous system, containing the regulation of motor functions, arousal, motivation and reward processing. Therefore, precise measurement of DA concentrations is vital for studying different dopaminergic neural pathways and for the diagnosis of neurological disorders. Herein, we developed a new semiconductor surface-enhanced Raman spectroscopic (SERS) platform designed for the real-time monitoring DA release from live cells with high selectivity and sensitivity. The sea urchin-like Bi2S3@Co3O4 composite substrate exhibited not only a wide linear range from 1.00 to 1.00 × 103 nmol/L but also a limit of detection (LOD) as low as 0.92 nmol/L for Methylene Blue (MB) molecules. In addition, we monitored DA release during the differentiation of neural stem cells (NSCs) into dopaminergic neurons by virtue of our constructed SERS platform in a nondestructive and in situ manner. Consequently, the developed SERS platform facilitates the direct detection of exocytotic DA from neuronal cells, enabling real-time assessment of cell viability in models of neurodegenerative disease-related cellular damage.

Antibodies in neurological diseases: Established, emerging, explorative

Within a few years, autoantibodies targeting the nervous system resulted in a novel disease classification. For several of them, which we termed 'established', direct pathogenicity has been proven and now guides diagnostic pathways and early immunotherapy. For a rapidly growing number of further anti-neuronal autoantibodies, the role in disease is less clear. Increasing evidence suggests that they could contribute to disease, by playing a modulating role on brain function. We therefore suggest a three-level classification of neurological autoantibodies according to the degree of experimentally proven pathogenicity and strength of clinical association: established, emerging, explorative. This may facilitate focusing on clinical constellations in which autoantibody-mediated mechanisms have not been assumed previously, including autoimmune psychosis and dementia, cognitive impairment in cancer, and neurodegenerative diseases. Based on recent data reviewed here, humoral autoimmunity may represent an additional "super-system" for brain health. The "brain antibody-ome", that is, the composition of thousands of anti-neuronal autoantibodies, may shape neuronal function not only in disease, but even in healthy aging. Towards this novel concept, extensive research will have to elucidate pathogenicity from the atomic to the clinical level, autoantibody by autoantibody. Such profiling can uncover novel biomarkers, enhance our understanding of underlying mechanisms, and identify selective therapies.

Pregnancy in myasthenia gravis: a retrospective analysis of maternal and neonatal outcome from a large tertiary care centre in Germany

PURPOSE

Myasthenia gravis (MG) is a rare, potentially life-threatening autoimmune disease with fluctuating muscle weakness frequently affecting women of childbearing age. MG can affect maternal as well as neonatal outcome with risk of worsening of myasthenic symptoms in the mothers and risk of transient neonatal myasthenia gravis (TNMG) and arthrogryposis multiplex congenita (AMC) or foetal acetylcholine receptor antibody-associated disorders (FARAD) in the neonates.

METHODS

Retrospective analysis of maternal and neonatal outcome in a cohort of pregnant MG patients treated at a tertiary care centre in Germany.

RESULTS

Overall, 66 pregnancies were analysed. During 40 (63%) pregnancies, women experienced a worsening of myasthenic symptoms, of whom 10 patients (15.7%) needed acute therapy with IVIg or plasma exchange. There was no case of myasthenic crisis. Rate of caesarean section was comparable to the overall C-section rate at our centre (38% vs. 40%). However, there was a slightly higher rate for operative vaginal delivery (15% vs. 10%) as potential indicator for fatiguing striated musculature in MG patients during the expulsion stage. Rate of TNMG as well as AMC was 3% (two cases each).

CONCLUSIONS

Maternal and neonatal outcome in our cohort was favourable with a low rate of myasthenic exacerbations requiring acute therapies and a low rate of TNMG and AMC/FARAD. Our data might help neurologists and obstetricians to advice MG patients with desire to have children.

Transient Neonatal Myasthenia Gravis as a Common Complication of a Rare Disease: A Systematic Review

Myasthenia gravis (MG) is a rare autoimmune disease. Transient neonatal myasthenia gravis (TNMG) is caused by pathogenic maternal autoantibodies that cross the placenta and disrupt signaling at the neuromuscular junction. This is a systematic review of this transient immunoglobulin G (IgG)-mediated disease. TNMG affects 10-20% of children born to mothers with MG. The severity of symptoms ranges from minor feeding difficulties to life-threatening respiratory weakness. Minor symptoms might go unnoticed but can still interfere with breastfeeding. Acetylcholine-esterase inhibitors and antibody-clearing therapies such as immunoglobulins can be used to treat TNMG, but most children do well with observation only. TNMG is self-limiting within weeks as circulating antibodies are naturally cleared from the blood. In rare cases, TNMG is associated with permanent skeletal malformations or permanent myopathy. The mother's antibodies can also lead to spontaneous abortions. All healthcare professionals meeting pregnant or birthing women with MG or their neonates should be aware of TNMG. TNMG is hard to predict. Reoccurrence is common among siblings. Pre-pregnancy thymectomy and intravenous immunoglobulins during pregnancy reduce the risk. Neonatal fragment crystallizable receptor (FcRn) blocking drugs for MG might reduce TNMG risk.

Maternal immunoglobulin treatment can reduce severity of fetal acetylcholine receptor antibody-associated disorders (FARAD)

BACKGROUND

Fetal acetylcholine receptor antibody-associated disorders (FARAD), caused by in utero exposure to maternal antibodies directed against the fetal acetylcholine receptor (AChR), is a rare condition occurring in newborns of myasthenic mothers. Only two cases of FARAD children born to asymptomatic mothers are published.

CASE

We report a completely asymptomatic mother of two FARAD children presenting exclusively with positive AChR antibodies. After birth, the first child needed intensive care therapy due to generalized hypotonia, respiratory problems, dysphagia, necessitating tube feeding and gastrostomy. FARAD was suspected because of ptosis, a hypomimic face, and confirmed by increased AChR antibodies in the mother. The mother became pregnant again 2 years later. Since FARAD is likely to reoccur and it is known that intensity of maternal myasthenia gravis treatment determines postnatal outcome, monthly intravenous immunoglobulin (IVIG) therapy was started at 12 weeks gestational age. The second child needed a short mask ventilation for initial stabilization at birth, but her muscle weakness improved rapidly and tube feeding was not necessary. Similar to her sister a tent-shaped mouth and a somewhat myopathic face persisted, but motor milestones were reached in time.

CONCLUSIONS

These observations highlight that FARAD is an important differential diagnosis of genetically determined congenital neuromuscular disorders even in asymptomatic mothers, and that IVIG therapy during the pregnancy has the potential to improve the outcome of the children.

The emerging spectrum of fetal acetylcholine receptor antibody-related disorders (FARAD)

In utero exposure to maternal antibodies targeting the fetal acetylcholine receptor isoform (fAChR) can impair fetal movement, leading to arthrogryposis multiplex congenita (AMC). Fetal AChR antibodies have also been implicated in apparently rare, milder myopathic presentations termed fetal acetylcholine receptor inactivation syndrome (FARIS). The full spectrum associated with fAChR antibodies is still poorly understood. Moreover, since some mothers have no myasthenic symptoms, the condition is likely underreported, resulting in failure to implement effective preventive strategies. Here we report clinical and immunological data from a multicentre cohort (n = 46 cases) associated with maternal fAChR antibodies, including 29 novel and 17 previously reported with novel follow-up data. Remarkably, in 50% of mothers there was no previously established myasthenia gravis (MG) diagnosis. All mothers (n = 30) had AChR antibodies and, when tested, binding to fAChR was often much greater than that to the adult AChR isoform. Offspring death occurred in 11/46 (23.9%) cases, mainly antenatally due to termination of pregnancy prompted by severe AMC (7/46, 15.2%), or during early infancy, mainly from respiratory failure (4/46, 8.7%). Weakness, contractures, bulbar and respiratory involvement were prominent early in life, but improved gradually over time. Facial (25/34; 73.5%) and variable peripheral weakness (14/32; 43.8%), velopharyngeal insufficiency (18/24; 75%) and feeding difficulties (16/36; 44.4%) were the most common sequelae in long-term survivors. Other unexpected features included hearing loss (12/32; 37.5%), diaphragmatic paresis (5/35; 14.3%), CNS involvement (7/40; 17.5%) and pyloric stenosis (3/37; 8.1%). Oral salbutamol used empirically in 16/37 (43.2%) offspring resulted in symptom improvement in 13/16 (81.3%). Combining our series with all previously published cases, we identified 21/85 mothers treated with variable combinations of immunotherapies (corticosteroids/intravenous immunoglobulin/plasmapheresis) during pregnancy either for maternal MG symptom control (12/21 cases) or for fetal protection (9/21 cases). Compared to untreated pregnancies (64/85), maternal treatment resulted in a significant reduction in offspring deaths (P < 0.05) and other complications, with treatment approaches involving intravenous immunoglobulin/ plasmapheresis administered early in pregnancy most effective. We conclude that presentations due to in utero exposure to maternal (fetal) AChR antibodies are more common than currently recognized and may mimic a wide range of neuromuscular disorders. Considering the wide clinical spectrum and likely diversity of underlying mechanisms, we propose 'fetal acetylcholine receptor antibody-related disorders' (FARAD) as the most accurate term for these presentations. FARAD is vitally important to recognize, to institute appropriate management strategies for affected offspring and to improve outcomes in future pregnancies. Oral salbutamol is a symptomatic treatment option in survivors.

Sex differences in neuromuscular disorders

The prevalence, onset, pathophysiology, and clinical course of many neuromuscular disorders (NMDs) may significantly differ between males and females. Some NMDs are more frequently observed in females, and characterized to show a higher grade of severity during or after the pregnancy. Meanwhile, others tend to have an earlier onset in males and exhibit a more variable progression. Prevalently, sex differences in NMDs have a familiar character given from genetic inheritance. However, they may also influence clinical presentation and disease severity of acquired NMD forms, and are represented by both hormonal and genetic factors. Consequently, to shed light on the distinctive role of biological factors in the different clinical phenotypes, we summarize in this review the sex related differences and their distinctive biological roles emerging from the current literature in both acquired and inherited NMDs.

Treatment considerations in myasthenia gravis for the pregnant patient

INTRODUCTION

Myasthenia gravis (MG) is an autoimmune disease where muscle antibodies form against the acetylcholine receptor (AChR), MuSK, or LRP4 at the neuromuscular junction leading to weakness. Patients worry about consequences for pregnancy, giving birth, nursing, and child outcome.

AREAS COVERED

This review lists the pharmacological treatments for MG in the reproductive age and gives recommendations. Consequences for pregnancy, giving birth, breastfeeding, and child outcome are discussed.

EXPERT OPINION

Pyridostigmine, corticosteroids in low doses, and azathioprine are regarded as safe during pregnancy and should be continued. Mycophenolate mofetil, methotrexate, and cyclophosphamide should not be used in reproductive age. Rituximab should not be given during pregnancy. Other monoclonal IgG antibodies such as eculizumab and efgartigimod should be given only when regarded strictly necessary to avoid long-term and severe incapacity. Intravenous and subcutaneous immunoglobulin and plasma exchange are safe treatments during pregnancy and are recommended for exacerbations with moderate or severe generalized weakness. Most MG women have spontaneous vaginal deliveries. Indications for Cesarean section are obstetrical and similar to non-MG women. Neonatal myasthenia manifests as a transient weakness caused by the mother's IgG muscle antibodies and affects 10% of the babies. MG women should be supported in their wish to have children.

Diagnostic workup in children with arthrogryposis: description of practices from a single reference centre, comparison with literature and suggestion of recommendations

INTRODUCTION

Arthrogryposis multiplex congenita (AMC) refers to a clinical presentation of congenital contractures involving two or more body areas. More than 400 distinct conditions may lead to AMC, making the aetiological diagnosis challenging. The objective of this work was to set up evidence-based recommendations for the diagnosis of AMC by taking advantage of both data from our nation-wide cohort of children with AMC and from the literature.

MATERIAL AND METHODS

We conducted a retrospective single-centre observational study. Patients had been evaluated at least once at a paediatric age in the AMC clinic of Grenoble University Hospital between 2007 and 2019. After gathering data about their diagnostic procedure, a literature review was performed for each paraclinical investigation to discuss their relevance.

RESULTS

One hundred and twenty-five patients were included, 43% had Amyoplasia, 27% had distal arthrogryposis and 30% had other forms. A definitive aetiological diagnosis was available for 66% of cases. We recommend a two-time diagnostic process: first, non-invasive investigations that aim at classifying patients into one of the three groups, and second, selected investigations targeting a subset of patients.

CONCLUSION

The aetiological management for patients with AMC remains arduous. This process will be facilitated by the increasing use of next-generation sequencing combined with detailed phenotyping. Invasive investigations should be avoided because of their limited yield.

Pregnancy and Autoimmune Disease

BACKGROUND

Pregnancies in women with chronic disease are on the rise. This pertains to autoimmune diseases in particular since these tend to affect women of childbearing age. The interaction between pregnancy and autoimmune disease may increase the risk of maternal, fetal, and obstetric complications; additional care may be required.

METHODS

This review is based on a selective literature search in PubMed (2015-2020).

RESULTS

In women with autoimmune diseases, the course of pregnancy is highly variable. Some autoimmune diseases tend to improve during pregnancy and do not to result in any serious obstetric complications. Others may worsen during pregnancy, with deterioration of the maternal condition as well as obstetric and perinatal complications. In systemic lupus erythematosus and myasthenia gravis, placental transfer of specific autoantibodies may cause fetal or neonatal disease.

CONCLUSION

The care of pregnant women with chronic diseases requires collaboration between specialists of the pertinent levels of care. A stable course of disease before conception, close interdisciplinary care, and pregnancy-compatible medication contribute to a reduction in maternal and perinatal complications.

Autoantibodies in neurological disease

The realization that autoantibodies can contribute to dysfunction of the brain has brought about a paradigm shift in neurological diseases over the past decade, offering up important novel diagnostic and therapeutic opportunities. Detection of specific autoantibodies to neuronal or glial targets has resulted in a better understanding of central nervous system autoimmunity and in the reclassification of some diseases previously thought to result from infectious, 'idiopathic' or psychogenic causes. The most prominent examples, such as aquaporin 4 autoantibodies in neuromyelitis optica or NMDAR autoantibodies in encephalitis, have stimulated an entire field of clinical and experimental studies on disease mechanisms and immunological abnormalities. Also, these findings inspired the search for additional autoantibodies, which has been very successful to date and has not yet reached its peak. This Review summarizes this rapid development at a point in time where preclinical studies have started delivering fundamental new data for mechanistic understanding, where new technologies are being introduced into this field, and - most importantly - where the first specifically tailored immunotherapeutic approaches are emerging.

Inhibition of Maternal-to-Fetal Transfer of IgG Antibodies by FcRn Blockade in a Mouse Model of Arthrogryposis Multiplex Congenita

Objective

To determine whether blocking the neonatal Fc receptor (FcRn) during gestation with an anti-FcRn monoclonal antibody (mAb) reduces transfer of pathogenic maternal antibodies in utero and decreases the likelihood of maternal antibody-mediated neonatal disease in the offspring.

Methods

Using a previously established maternal-to-fetal transfer mouse model of arthrogryposis multiplex congenita (AMC), we assessed the effect of 4470, an anti-FcRn mAb, on the transfer of total human immunoglobulin G (IgG) and specific acetylcholine receptor (AChR)-antibodies from mother to fetus, as well as its effect on the prevention of neurodevelopmental abnormalities in the offspring.

Results

Offspring of pregnant dams treated with 4470 during gestation showed a substantial reduction in total human IgG and AChR antibody levels compared with those treated with the isotype mAb control. Treatment with 4470 was also associated with a significant reduction in AMC-IgG–induced deformities (limb or spinal curve malformations) when compared with mAb control–exposed embryos and a nonsignificant increase in the percentage of fetuses showing spontaneous movements. 4470 exposure during pregnancy was not associated with changes in general parameters of maternal well-being or fetal development; indeed, male neonates showed faster weight gain and shorter time to reach developmental milestones.

Conclusions

FcRn blockade is a promising therapeutic strategy to prevent the occurrence of AMC and other human maternal autoantibody-related diseases in the offspring.

Myasthenia Gravis: Epidemiology, Pathophysiology and Clinical Manifestations

Myasthenia gravis (MG) is an autoimmune neurological disorder characterized by defective transmission at the neuromuscular junction. The incidence of the disease is 4.1 to 30 cases per million person-years, and the prevalence rate ranges from 150 to 200 cases per million. MG is considered a classic example of antibody-mediated autoimmune disease. Most patients with MG have autoantibodies against the acetylcholine receptors (AChRs). Less commonly identified autoantibodies include those targeted to muscle-specific kinase (MuSK), low-density lipoprotein receptor-related protein 4 (Lrp4), and agrin. These autoantibodies disrupt cholinergic transmission between nerve terminals and muscle fibers by causing downregulation, destruction, functional blocking of AChRs, or disrupting the clustering of AChRs in the postsynaptic membrane. The core clinical manifestation of MG is fatigable muscle weakness, which may affect ocular, bulbar, respiratory and limb muscles. Clinical manifestations vary according to the type of autoantibody, and whether a thymoma is present.

Myasthenia gravis and pregnancy

Myasthenia gravis is an autoimmune disease characterised by fluctuating muscle weakness, which worsens during activity. It affects particularly scapular and pelvic girdles, axial and bulbar muscles. Myasthenia gravis is twice more frequent in women and symptoms often appear in the second and third decade of life. Thus, a growing number of women affected by this condition become pregnant. To minimise the effects of myasthenia gravis on pregnancy and the newborn, and to avoid myasthenia crisis in the post-partum, the pregnancy must be planned as far as possible. During pregnancy, treatment must be reviewed due to the threat of teratogenic effects (mycophenolate mofetil, rituximab), and the follow-up must be multidisciplinary.

Spread spectrum SERS allows label-free detection of attomolar neurotransmitters

The quantitative label-free detection of neurotransmitters provides critical clues in understanding neurological functions or disorders. However, the identification of neurotransmitters remains challenging for surface-enhanced Raman spectroscopy (SERS) due to the presence of noise. Here, we report spread spectrum SERS (ss-SERS) detection for the rapid quantification of neurotransmitters at the attomolar level by encoding excited light and decoding SERS signals with peak autocorrelation and near-zero cross-correlation. Compared to conventional SERS measurements, the experimental result of ss-SERS shows an exceptional improvement in the signal-to-noise ratio of more than three orders of magnitude, thus achieving a high temporal resolution of over one hundred times. The ss-SERS measurement further allows the attomolar SERS detection of dopamine, serotonin, acetylcholine, γ-aminobutyric acid, and glutamate without Raman reporters. This approach opens up opportunities not only for investigating the early diagnostics of neurological disorders or highly sensitive biomedical SERS applications but also for developing low-cost spectroscopic biosensing applications.

Identification of neurotransmitters remains challenging for surface enhanced Raman spectroscopy (SERS) due to presence of noise. Here, the authors present spread spectrum SERS, which by encoding excited light and decoding SERS signals enables detection of unlabelled neurotransmitters at attomolar concentrations.

The Structure, Function, and Physiology of the Fetal and Adult Acetylcholine Receptor in Muscle

The neuromuscular junction (NMJ) is a highly developed synapse linking motor neuron activity with muscle contraction. A complex of molecular cascades together with the specialized NMJ architecture ensures that each action potential arriving at the motor nerve terminal is translated into an action potential in the muscle fiber. The muscle-type nicotinic acetylcholine receptor (AChR) is a key molecular component located at the postsynaptic muscle membrane responsible for the generation of the endplate potential (EPP), which usually exceeds the threshold potential necessary to activate voltage-gated sodium channels and triggers a muscle action potential. Two AChR isoforms are found in mammalian muscle. The fetal isoform is present in prenatal stages and is involved in the development of the neuromuscular system whereas the adult isoform prevails thereafter, except after denervation when the fetal form is re-expressed throughout the muscle. This review will summarize the structural and functional differences between the two isoforms and outline congenital and autoimmune myasthenic syndromes that involve the isoform specific AChR subunits.

Gender issues of antibody-mediated diseases in neurology: (NMOSD/autoimmune encephalitis/MG)

Neuromyelitis optica spectrum disorder (NMOSD), autoimmune encephalitis (AE), myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) are antibody-mediated neurological diseases. They have mostly female predominance, affecting many women during childbearing age. Interactions between the underlying disease (or necessary treatment) and pregnancy can occur in every of these illnesses. Herein, we present the characteristics of NMOSD, AE, MG and LEMS in general, and review published data regarding the influence of the different diseases on fertility, pregnancy, puerperium, treatment strategy during pregnancy and post-partum period, and menopause but also male factors. We summarise key elements that should be borne in mind when confronted with such cases.

Management of Juvenile Myasthenia Gravis

Juvenile Myasthenia Gravis (JMG) is a rare disorder, defined as myasthenia gravis in children younger than 18 years of age. While clinical phenotypes are similar to adults, there are a number of caveats that influence management: broader differential diagnoses; higher rates of spontaneous remission; and the need to initiate appropriate treatment early, to avoid the long-term physical and psychosocial morbidity. Current practice is taken from treatment guidelines for adult MG or individual experience, with considerable variability seen across centers. We discuss our approach to treating JMG, in a large specialist JMG service, and review currently available evidence and highlight potential areas for future research. First-line treatment of generalized JMG is symptomatic management with pyridostigmine, but early use of immunosuppression, where good control is not achieved is important. Oral prednisolone is used as first-line immunosuppression with appropriate prevention and monitoring of side effects. Second-line therapies including azathioprine and mycophenolate may be considered where there is: no response to steroids, inability to wean to a reasonable minimum effective dose or if side-effects are intolerable. Management of ocular JMG is similar, but requires close involvement of ophthalmology in young children to prevent amblyopia. Muscle-specific tyrosine kinase (MuSK)-JMG show a poorer response to pyridostigmine and anecdotal evidence suggests that rituximab should be considered as second-line immunosuppression. Thymectomy is indicated in any patient with a thymoma, and consideration should be given in acetylcholine receptor (AChR) positive JMG allowing time for spontaneous remission. The benefit is less clear in ocular JMG and is not advised in MuSK-JMG. Children experiencing a myasthenic crisis require urgent hospital admission with access to the intensive care unit. PLEX is preferred over IVIG due to rapid onset of action, but this needs to be balanced with feasibility in very young children. Key questions remain in the management of JMG: when to initiate both first- and second-line treatments, choosing between steroid-sparing agents, and determining the optimal dose and treatment duration. We feel that given the rarity of this disease, the establishment of national registries and collaboration across groups will be needed to address these issues and facilitate future drug trials in JMG.

A Practical Approach to Managing Patients With Myasthenia Gravis-Opinions and a Review of the Literature

When the diagnosis of myasthenia gravis (MG) has been secured, the aim of management should be prompt symptom control and the induction of remission or minimal manifestations. Symptom control, with acetylcholinesterase inhibitors such as pyridostigmine, is commonly employed. This may be sufficient in mild disease. There is no single universally accepted treatment regimen. Corticosteroids are the mainstay of immunosuppressive treatment in patients with more than mild MG to induce remission. Immunosuppressive therapies, such as azathioprine are prescribed in addition to but sometimes instead of corticosteroids when background comorbidities preclude or restrict the use of steroids. Rituximab has a role in refractory MG, while plasmapheresis and immunoglobulin therapy are commonly prescribed to treat MG crisis and in some cases of refractory MG. Data from the MGTX trial showed clear evidence that thymectomy is beneficial in patients with acetylcholine receptor (AChR) antibody positive generalized MG, up to the age of 65 years. Minimally invasive thymectomy surgery including robotic-assisted thymectomy surgery has further revolutionized thymectomy and the management of MG. Ocular MG is not life-threatening but can be significantly disabling when diplopia is persistent. There is evidence to support early treatment with corticosteroids when ocular motility is abnormal and fails to respond to symptomatic treatment. Treatment needs to be individualized in the older age-group depending on specific comorbidities. In the younger age-groups, particularly in women, consideration must be given to the potential teratogenicity of certain therapies. Novel therapies are being developed and trialed, including ones that inhibit complement-induced immunological pathways or interfere with antibody-recycling pathways. Fatigue is common in MG and should be duly identified from fatigable weakness and managed with a combination of physical therapy with or without psychological support. MG patients may also develop dysfunctional breathing and the necessary respiratory physiotherapy techniques need to be implemented to alleviate the patient's symptoms of dyspnoea. In this review, we discuss various facets of myasthenia management in adults with ocular and generalized disease, including some practical approaches and our personal opinions based on our experience.

Myasthenia Gravis Can Have Consequences for Pregnancy and the Developing Child

Myasthenia gravis (MG) with onset below 50 years, thymic hyperplasia and acetylcholine receptor (AChR) antibodies is more common in females than in males. For a relatively large group of MG patients, pregnancy represents therefore an important question. The muscle weakness, the circulating autoantibodies, the hyperplastic thymus, the MG drug treatment, and any autoimmune comorbidity may all influence both mother and child health during pregnancy and also during breastfeeding in the postpartum period. Mother's MG remains stable in most patients during pregnancy. Pyridostigmine, prednisolone, and azathioprine are regarded as safe during pregnancy. Mycophenolate, methotrexate and cyclophosphamide are teratogenic and should not be used by women with the potential to become pregnant. Rituximab should not be given during the last few months before conception and not during pregnancy. Intravenous immunoglobulin and plasma exchange can be used for exacerbations or when need for intensified therapy. Pregnancies in MG women are usually without complications. Their fertility is near normal. Vaginal delivery is recommended. MG patients have an increased rate of Cesarean section, partly due to their muscle weakness and to avoid exhaustion, partly as a precaution that is often unnecessary. Around 10% of the newborn develop neonatal myasthenia during the first few days after birth. This is transient and usually mild with some sucking and swallowing difficulties. In rare cases, transplacental transfer of AChR antibodies leads to permanent muscle weakness in the child, and arthrogryposis with joint contractures. Repeated spontaneous abortions have been described due to AChR antibodies. MG women should always give birth at hospitals with experience in newborn intensive care. MG does not represent a reason for not having children, and the patients should be supported in their wish of becoming pregnant.

ANTIBODIES AND RECEPTORS: From Neuromuscular Junction to Central Nervous System

Myasthenia gravis (MG) is a relatively rare neurological disease that is usually associated with antibodies to the acetylcholine receptor (AChR). These antibodies (Abs) cause loss of the AChRs from the neuromuscular junction (NMJ), resulting in muscle weakness that can be life-threatening. Another form of the disease is caused by antibodies to muscle specific kinase (MuSK) that result in impaired AChR clustering and numbers at the NMJ, and may also interfere with presynaptic adaptive mechanisms. Other autoimmune disorders, Lambert Eaton myasthenic syndrome and acquired neuromyotonia, are associated with antibodies to presynaptic voltage-gated calcium and potassium channels respectively. All four conditions can be diagnosed by specific clinical features, electromyography and serum antibody tests, and can be treated effectively by a combination of pharmacological approaches and procedures that reduce the levels of the IgG antibodies. They form the first of a spectrum of diseases in which serum autoantibodies bind to extracellular domains of neuronal proteins throughout the nervous system and lead to constellations of clinical features including paralysis, sensory disturbance and pain, memory loss, seizures, psychiatric disturbance and movement disorders. This review will briefly summarize the ways in which this field has developed, since the 1970s when considerable contributions were made in Ricardo Miledi's laboratory at UCL.

Myasthenia Gravis: Pathogenic Effects of Autoantibodies on Neuromuscular Architecture

Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction (NMJ). Autoantibodies target key molecules at the NMJ, such as the nicotinic acetylcholine receptor (AChR), muscle-specific kinase (MuSK), and low-density lipoprotein receptor-related protein 4 (Lrp4), that lead by a range of different pathogenic mechanisms to altered tissue architecture and reduced densities or functionality of AChRs, reduced neuromuscular transmission, and therefore a severe fatigable skeletal muscle weakness. In this review, we give an overview of the history and clinical aspects of MG, with a focus on the structure and function of myasthenic autoantigens at the NMJ and how they are affected by the autoantibodies' pathogenic mechanisms. Furthermore, we give a short overview of the cells that are implicated in the production of the autoantibodies and briefly discuss diagnostic challenges and treatment strategies.

Maternal myasthenia gravis represents a risk for the child through autoantibody transfer, immunosuppressive therapy and genetic influence

Females with myasthenia gravis (MG) worry about their disease having negative consequences for their children. Autoimmune disease mechanisms, treatment and heredity could all have an impact on the child. This is a subject review where Web of Science was searched for relevant keywords and combinations. Controlled and prospective studies were included, and also results from selected and unselected patient cohorts, guidelines, consensus papers and reviews. Neonatal MG with temporary muscle weakness occurs in 10% of newborn babies where the mother has MG, due to transplacental transfer of antibodies against acetylcholine receptor (AChR), muscle-specific kinase (MuSK) or lipoprotein receptor-related protein 4 (LRP4). Arthrogryposis and fetal AChR inactivation syndrome with contractures and permanent myopathy are rare events caused by mother's antibodies against fetal type AChR. The MG drugs pyridostigmine, prednisolone and azathioprine are regarded as safe during pregnancy and breastfeeding. Methotrexate, mycophenolate mofetil and cyclophosphamide are teratogenic. Mother's MG implies at least a 10-fold increased risk for MG and other autoimmune diseases in the child. MG females should receive specific information about pregnancy and giving birth. First-line MG treatments should usually be continued during pregnancy. Intravenous immunoglobulin and plasma exchange represent safe treatments for exacerbations. Neonatal MG risk means that MG women should give birth at hospitals experienced in neonatal intensive care. Neonatal MG needs supportive care, rarely also acetylcholine esterase inhibition or intravenous immunoglobulin. Women with MG should be supported in their wish to have children.

Congenital myopathies: disorders of excitation-contraction coupling and muscle contraction

The congenital myopathies are a group of early-onset, non-dystrophic neuromuscular conditions with characteristic muscle biopsy findings, variable severity and a stable or slowly progressive course. Pronounced weakness in axial and proximal muscle groups is a common feature, and involvement of extraocular, cardiorespiratory and/or distal muscles can implicate specific genetic defects. Central core disease (CCD), multi-minicore disease (MmD), centronuclear myopathy (CNM) and nemaline myopathy were among the first congenital myopathies to be reported, and they still represent the main diagnostic categories. However, these entities seem to belong to a much wider phenotypic spectrum. To date, congenital myopathies have been attributed to mutations in over 20 genes, which encode proteins implicated in skeletal muscle Ca²⁺ homeostasis, excitation-contraction coupling, thin-thick filament assembly and interactions, and other mechanisms. RYR1 mutations are the most frequent genetic cause, and CCD and MmD are the most common subgroups. Next-generation sequencing has vastly improved mutation detection and has enabled the identification of novel genetic backgrounds. At present, management of congenital myopathies is largely supportive, although new therapeutic approaches are reaching the clinical trial stage.

Serological and experimental studies in different forms of myasthenia gravis

Antibodies to the acetylcholine receptor (AChR) have been recognized for over 40 years and have been important in the diagnosis of myasthenia gravis (MG), and its recognition in patients of different ages and thymic pathologies. The 10-20% of patients who do not have AChR antibodies are now known to comprise different subgroups, the most commonly reported of which is patients with antibodies to muscle-specific kinase (MuSK). The use of cell-based assays has extended the repertoire of antibody tests to clustered AChRs, low-density lipoprotein receptor-related protein 4, and agrin. Autoantibodies against intracellular targets, namely cortactin, titin, and ryanodine receptor (the latter two being associated with the presence of thymoma), may also be helpful as biomarkers in some patients. IgG4 MuSK antibodies are clearly pathogenic, but the coexisting IgG1, IgG2, and IgG3 antibodies, collectively, have effects that question the dominance of IgG4 as the sole pathologic factor in MuSK MG. After a brief historical review, we define the different subgroups and summarize the antibody characteristics. Experiments to demonstrate the in vitro and in vivo pathogenic roles of MuSK antibodies are discussed.

Characterization of an anti-fetal AChR monoclonal antibody isolated from a myasthenia gravis patient

We report here the sequence and functional characterization of a recombinantly expressed autoantibody (mAb 131) previously isolated from a myasthenia gravis patient by immortalization of thymic B cells using Epstein-Barr virus and TLR9 activation. The antibody is characterized by a high degree of somatic mutations as well as a 6 amino acid insertion within the VHCDR2. The recombinant mAb 131 is specific for the γ-subunit of the fetal AChR to which it bound with sub-nanomolar apparent affinity, and detected the presence of fetal AChR on a number of rhabdomyosarcoma cell lines. Mab 131 blocked one of the two α-bungarotoxin binding sites on the fetal AChR, and partially blocked the binding of an antibody (mAb 637) to the α-subunit of the AChR, suggesting that both antibodies bind at or near one ACh binding site at the α/γ subunit interface. However, mAb 131 did not reduce fetal AChR ion channel currents in electrophysiological experiments. These results indicate that mAb 131, although generated from an MG patient, is unlikely to be pathogenic and may make it a potentially useful reagent for studies of myasthenia gravis, rhabdomyosarcoma and arthrogryposis multiplex congenita which can be caused by fetal-specific AChR-blocking autoantibodies.

Synaptic Homeostasis and Its Immunological Disturbance in Neuromuscular Junction Disorders

In the neuromuscular junction, postsynaptic nicotinic acetylcholine receptor (nAChR) clustering, trans-synaptic communication and synaptic stabilization are modulated by the molecular mechanisms underlying synaptic plasticity. The synaptic functions are based presynaptically on the active zone architecture, synaptic vesicle proteins, Ca²⁺ channels and synaptic vesicle recycling. Postsynaptically, they are based on rapsyn-anchored nAChR clusters, localized sensitivity to ACh, and synaptic stabilization via linkage to the extracellular matrix so as to be precisely opposed to the nerve terminal. Focusing on neural agrin, Wnts, muscle-specific tyrosine kinase (a mediator of agrin and Wnts signalings and regulator of trans-synaptic communication), low-density lipoprotein receptor-related protein 4 (the receptor of agrin and Wnts and participant in retrograde signaling), laminin-network (including muscle-derived agrin), extracellular matrix proteins (participating in the synaptic stabilization) and presynaptic receptors (including muscarinic and adenosine receptors), we review the functional structures of the synapse by making reference to immunological pathogenecities in postsynaptic disease, myasthenia gravis. The synapse-related proteins including cortactin, coronin-6, caveolin-3, doublecortin, R-spondin 2, amyloid precursor family proteins, glia cell-derived neurotrophic factor and neurexins are also discussed in terms of their possible contribution to efficient synaptic transmission at the neuromuscular junction.

Neuromuscular junction disorders

Diseases of the neuromuscular junction comprise a wide range of disorders. Antibodies, genetic mutations, specific drugs or toxins interfere with the number or function of one of the essential proteins that control signaling between the presynaptic nerve ending and the postsynaptic muscle membrane. Acquired autoimmune disorders of the neuromuscular junction are the most common and are described here. In myasthenia gravis, antibodies to acetylcholine receptors or to proteins involved in receptor clustering, particularly muscle-specific kinase, cause direct loss of acetylcholine receptors or interfere with the agrin-induced acetylcholine receptor clustering necessary for efficient neurotransmission. In the Lambert-Eaton myasthenic syndrome (LEMS), loss of the presynaptic voltage-gated calcium channels results in reduced release of the acetylcholine transmitter. The conditions are generally recognizable clinically and the diagnosis confirmed by serologic testing and electromyography. Screening for thymomas in myasthenia or small cell cancer in LEMS is important. Fortunately, a wide range of symptomatic treatments, immunosuppressive drugs, or other immunomodulating therapies is available. Future research is directed to understanding the pathogenesis, discovering new antigens, and trying to develop disease-specific treatments.

Antibodies as Mediators of Brain Pathology

The brain is normally sequestered from antibody exposure by the blood brain barrier. However, antibodies can access the brain during fetal development before the barrier achieves full integrity, and in disease states when barrier integrity is compromised. Recent studies suggest that antibodies contribute to brain pathology associated with autoimmune diseases such as systemic lupus erythematosus and neuromyelitis optica, and can lead to transient or permanent behavioral or cognitive abnormalities. We review these findings here and examine the circumstances associated with antibody entry into the brain, the routes of access and the mechanisms that then effect pathology. Understanding these processes and the nature and specificity of neuronal autoantibodies may reveal therapeutic strategies toward alleviating or preventing the neurological pathologies and behavioral abnormalities associated with autoimmune disease.