Anti-LRP4 autoantibodies in AChR- and MuSK-antibody-negative myasthenia gravis

Complement system activation: bridging physiology, pathophysiology, and therapy

The complement system is a set of over 50 proteins that constitutes an essential part of the innate immune system. Complement system activation involves an organized proteolytic cascade. Overactivation of complement system activation is the main pathogenic mechanism of several diseases and contributes to the manifestations of many other conditions. This review describes the normal complement system and the role for complement dysregulation in critical illnesses, notably sepsis and acute respiratory distress syndrome. Complement activation is involved in the immune system response to pathogens but, when excessive, can contribute to tissue damage, runaway inflammation, and capillary leakage syndrome. Complement overactivation may play a key role in severe forms of coronavirus disease 2019 (COVID-19). Two diseases whose manifestations are mainly caused by complement overactivation, namely, atypical hemolytic and uremic syndrome (aHUS) and myasthenia gravis, are discussed. A diagnostic algorithm for aHUS is provided. Early complement-inhibiting therapy has been proven effective. When renal transplantation is required, complement-inhibiting drugs can be used prophylactically to prevent aHUS recurrence. Similarly, acetylcholine-receptor autoantibody-positive generalized myasthenia gravis involves complement system overactivation and responds to complement inhibition. The two main complement inhibitors used in to date routine are eculizumab and ravulizumab. The main adverse event is Neisseria infection, which is rare and preventable, but can be fatal. The complement system is crucial to health but, when overactivated, can cause or contribute to disease. Effective complement inhibitors are now available, although additional data are required to determine optimal regimens. Further research is also needed to better understand the complement system, develop advanced diagnostic tools, and identify markers that allow the personalization of treatment strategies.

Lipoprotein Receptor-Related Protein 4 Antibody Positivity in the Youngest Patient in the Caucasus Region: A Case Report

Juvenile myasthenia gravis is a rare disorder where antibodies targeting the acetylcholine receptor or, less frequently, muscle-specific kinase can be detected in the serum while about half of the patients can be seronegative. A pediatric patient with ocular myasthenia is presented whose serum was negative for acetylcholine receptor and muscle-specific kinase antibodies but tested positive for low-density lipoprotein receptor-related protein 4 antibodies. A favourable clinical response was observed to medical treatment with pyridostigmine and prednisolone, as expected in isolated ocular juvenile myasthenia gravis. This case exemplifies the very rare association of juvenile myasthenia gravis with low-density lipoprotein receptor-related protein 4 positivity, reported in only a few cases so far. The specificity of the antibody and the efficiency of medical treatment emphasize the importance of clinical suspicion and appropriate serological testing in juvenile myasthenia gravis in the absence of acetylcholine receptor and muscle-specific kinase antibodies.

Neuronal LRP4 directs the development, maturation and cytoskeletal organization of Drosophila peripheral synapses

Synaptic development requires multiple signaling pathways to ensure successful connections. Transmembrane receptors are optimally positioned to connect the synapse and the rest of the neuron, often acting as synaptic organizers to synchronize downstream events. One such organizer, the LDL receptor-related protein LRP4, is a cell surface receptor that has been most well-studied postsynaptically at mammalian neuromuscular junctions. Recent work, however, identified emerging roles, but how LRP4 acts as a presynaptic organizer and the downstream mechanisms of LRP4 are not well understood. Here, we show that LRP4 functions presynaptically at Drosophila neuromuscular synapses, acting in motoneurons to instruct pre- and postsynaptic development. Loss of presynaptic LRP4 results in multiple defects, impairing active zone organization, synapse growth, physiological function, microtubule organization, synaptic ultrastructure and synapse maturation. We further demonstrate that LRP4 promotes most aspects of presynaptic development via a downstream SR-protein kinase, SRPK79D. These data demonstrate a function for presynaptic LRP4 as a peripheral synaptic organizer, highlight a downstream mechanism conserved with its CNS function in Drosophila, and underscore previously unappreciated but important developmental roles for LRP4 in cytoskeletal organization, synapse maturation and active zone organization.

Functional Signature of LRP4 Antibodies in Myasthenia Gravis

BACKGROUND AND OBJECTIVES

Antibodies (Abs) specific for the low-density lipoprotein receptor-related protein 4 (LRP4) occur in up to 5% of patients with myasthenia gravis (MG). The objective of this study was to profile LRP4-Ab effector actions.

METHODS

We evaluated the efficacy of LRP4-specific compared with AChR-specific IgG to induce Ab-dependent cellular phagocytosis (ADCP), Ab-dependent cellular cytotoxicity (ADCC), and Ab-dependent complement deposition (ADCD). Functional features were additionally assessed in an independent AChR-Ab+ MG cohort. Levels of circulating activated complement proteins and frequency of Fc glycovariants were quantified and compared with demographically matched 19 healthy controls.

RESULTS

Effector actions that required binding of Fc domains to cellular FcRs such as ADCC and ADCP were detectable for both LRP4-specific and AChR-specific Abs. In contrast to AChR-Abs, LRP4-binding Abs showed poor efficacy in inducing complement deposition. Levels of circulating activated complement proteins were not substantially increased in LRP4-Ab-positive MG. Frequency of IgG glycovariants carrying 2 sialic acid residues, indicative for anti-inflammatory IgG activity, was decreased in patients with LRP4-Ab-positive MG.

DISCUSSION

LRP4-Abs are more effective in inducing cellular FcR-mediated effector mechanisms than Ab-dependent complement activation. Their functional signature is different from AChR-specific Abs.

Myasthenia Gravis Triggered by a COVID-19 Infection: A Case Report and Literature Review

Myasthenia gravis (MG) is an autoimmune disease that induces skeletal muscle weakness, affecting different muscle groups. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 2019 (COVID-19), became both a diagnostic and a therapeutic challenge during the pandemic. The effects of COVID-19 are not only limited to the acute symptoms but also to the post-infectious sequelae. We present the case of a 30-year-old Caucasian woman, with no significant medical history, who presented to the emergency room with acute respiratory failure. The patient tested positive for SARS-CoV-2 with a rapid antigen test and during hospitalization developed a myasthenic crisis, ultimately being diagnosed with seropositive MG.

Exploring the depths of IgG4: insights into autoimmunity and novel treatments

IgG4 subclass antibodies represent the rarest subclass of IgG antibodies, comprising only 3-5% of antibodies circulating in the bloodstream. These antibodies possess unique structural features, notably their ability to undergo a process known as fragment-antigen binding (Fab)-arm exchange, wherein they exchange half-molecules with other IgG4 antibodies. Functionally, IgG4 antibodies primarily block and exert immunomodulatory effects, particularly in the context of IgE isotype-mediated hypersensitivity reactions. In the context of disease, IgG4 antibodies are prominently observed in various autoimmune diseases combined under the term IgG4 autoimmune diseases (IgG4-AID). These diseases include myasthenia gravis (MG) with autoantibodies against muscle-specific tyrosine kinase (MuSK), nodo-paranodopathies with autoantibodies against paranodal and nodal proteins, pemphigus vulgaris and foliaceus with antibodies against desmoglein and encephalitis with antibodies against LGI1/CASPR2. Additionally, IgG4 antibodies are a prominent feature in the rare entity of IgG4 related disease (IgG4-RD). Intriguingly, both IgG4-AID and IgG4-RD demonstrate a remarkable responsiveness to anti-CD20-mediated B cell depletion therapy (BCDT), suggesting shared underlying immunopathologies. This review aims to provide a comprehensive exploration of B cells, antibody subclasses, and their general properties before examining the distinctive characteristics of IgG4 subclass antibodies in the context of health, IgG4-AID and IgG4-RD. Furthermore, we will examine potential therapeutic strategies for these conditions, with a special focus on leveraging insights gained from anti-CD20-mediated BCDT. Through this analysis, we aim to enhance our understanding of the pathogenesis of IgG4-mediated diseases and identify promising possibilities for targeted therapeutic intervention.

Juvenile ocular myasthenia gravis: a report of two cases

We report 2 cases of pediatric ocular myasthenia gravis. The first case was a 7-year-old girl who presented with bilateral ophthalmoplegia and ptosis that correlated with the onset of upper respiratory symptoms. Neuroimaging and acetylcholine receptor antibody testing were unremarkable. The ice pack test was positive. Symptoms greatly improved with pyridostigmine, with full resolution of ophthalmoplegia achieved by 8-month follow-up. The second case was a 4-year-old girl who presented emergently with ptosis and bilateral ophthalmoplegia. Acetylcholine receptor antibodies testing was positive. The patient was started on pyridostigmine and intravenous immunoglobulin and is scheduled to follow-up with pediatric ophthalmology in the outpatient setting.

Myasthenia gravis-Pathophysiology, diagnosis, and treatment

Myasthenia gravis (MG) is an autoimmune disease characterized by dysfunction of the neuromuscular junction resulting in skeletal muscle weakness. It is equally prevalent in males and females, but debuts at a younger age in females and at an older age in males. Ptosis, diplopia, facial bulbar weakness, and limb weakness are the most common symptoms. MG can be classified based on the presence of serum autoantibodies. Acetylcholine receptor (AChR) antibodies are found in 80%-85% of patients, muscle-specific kinase (MuSK) antibodies in 5%-8%, and <1% may have low-density lipoprotein receptor-related protein 4 (Lrp4) antibodies. Approximately 10% of patients are seronegative for antibodies binding the known disease-related antigens. In patients with AChR MG, 10%-20% have a thymoma, which is usually detected at the onset of the disease. Important differences between clinical presentation, treatment responsiveness, and disease mechanisms have been observed between these different serologic MG classes. Besides the typical clinical features and serologic testing, the diagnosis can be established with additional tests, including repetitive nerve stimulation, single fiber EMG, and the ice pack test. Treatment options for MG consist of symptomatic treatment (such as pyridostigmine), immunosuppressive treatment, or thymectomy. Despite the treatment with symptomatic drugs, steroid-sparing immunosuppressants, intravenous immunoglobulins, plasmapheresis, and thymectomy, a large proportion of patients remain chronically dependent on corticosteroids (CS). In the past decade, the number of treatment options for MG has considerably increased. Advances in the understanding of the pathophysiology have led to new treatment options targeting B or T cells, the complement cascade, the neonatal Fc receptor or cytokines. In the future, these new treatments are likely to reduce the chronic use of CS, diminish side effects, and decrease the number of patients with refractory disease.

Antibody Response to HERV-K and HERV-W Envelope Epitopes in Patients with Myasthenia Gravis

Myasthenia gravis is an antibody-mediated autoimmune neurological disorder characterized by impaired neuromuscular junction transmission, resulting in muscle weakness. Recently, the involvement of Human Endogenous Retroviruses (HERVs) in the pathophysiology of different immune-mediated and neurodegenerative diseases, such as multiple sclerosis, has been demonstrated. We aimed to investigate potential immune system involvement related to humoral responses targeting specific epitopes of HERV-K and HERV-W envelope proteins in myasthenia gravis. Myasthenia gravis patients were recruited in the Neurology Unit, while healthy controls were selected from the Blood Transfusion Center, both affiliated with AOU Sassari. Highly immunogenic antigens of HERV-K and HERV-W envelope proteins were identified using the Immune Epitope Database (IEDB) online tool. These epitopes were utilized in enzyme-linked immunosorbent assays (ELISA) to detect autoantibodies in serum directed against these sequences. The study involved 39 Healthy Donors and 47 MG patients, further categorized into subgroups based on the presence of autoantibodies: MG-AchR Ab+ (n = 17), MG-MuSK Ab+ (n = 7), double seronegative patients (MG-DSN, n = 18), MG-LRP4 Ab + (n = 4), and one patient with no antibodies data (n = 1). Our findings revealed high levels of autoantibodies in myasthenia gravis patients directed against the HERV-K-env-su(19-37), HERV-K-env-su(109-126), HERV-K-env-su(164-186), HERV-W-env(93-108), HERV-W-env(129-14), and HERV-W-env(248-262) epitopes. Notably, these results remained highly significant even when patients were subdivided into MG-AchR Ab+ and MG-DSN subgroups. Correlation analysis further revealed significant positive associations between the antibody levels against HERV-K and HERV-W families in patients, suggesting a synergistic action of the two HERVs in the pathology context since this correlation is absent in the control group. This study marks the first identification of a specific humoral response directed against defined epitopes of HERV-K and HERV-W envelope proteins in myasthenia gravis patients. These findings lay the foundation for future investigations aimed at elucidating the molecular mechanisms driving this immune response. The detection of these autoantibodies suggests the potential for novel biomarkers, especially within the MG-DSN patient subgroup, addressing the need for new biomarkers in this population.

Pathophysiology of Childhood-Onset Myasthenia: Abnormalities of Neuromuscular Junction and Autoimmunity and Its Background

The pathophysiology of myasthenia gravis (MG) has been largely elucidated over the past half century, and treatment methods have advanced. However, the number of cases of childhood-onset MG is smaller than that of adult MG, and the treatment of childhood-onset MG has continued to be based on research in the adult field. Research on pathophysiology and treatment methods that account for the unique growth and development of children is now desired. According to an epidemiological survey conducted by the Ministry of Health, Labour and Welfare of Japan, the number of patients with MG by age of onset in Japan is high in early childhood. In recent years, MG has been reported from many countries around the world, but the pattern of the number of patients by age of onset differs between East Asia and Western Europe, confirming that the Japanese pattern is common in East Asia. Furthermore, there are racial differences in autoimmune MG and congenital myasthenic syndromes according to immunogenetic background, and their pathophysiology and relationships are gradually becoming clear. In addition, treatment options are also recognized in different regions of the world. In this review article, I will present recent findings focusing on the differences in pathophysiology.

Neuronal LRP4 directs the development, maturation, and cytoskeletal organization of peripheral synapses

Synapse development requires multiple signaling pathways to accomplish the myriad of steps needed to ensure a successful connection. Transmembrane receptors on the cell surface are optimally positioned to facilitate communication between the synapse and the rest of the neuron and often function as synaptic organizers to synchronize downstream signaling events. One such organizer, the LDL receptor-related protein LRP4, is a cell surface receptor most well-studied postsynaptically at mammalian neuromuscular junctions. Recent work, however, has identified emerging roles for LRP4 as a presynaptic molecule, but how LRP4 acts as a presynaptic organizer, what roles LRP4 plays in organizing presynaptic biology, and the downstream mechanisms of LRP4 are not well understood. Here we show that LRP4 functions presynaptically at Drosophila neuromuscular synapses, acting in motor neurons to instruct multiple aspects of pre- and postsynaptic development. Loss of presynaptic LRP4 results in a range of developmental defects, impairing active zone organization, synapse growth, physiological function, microtubule organization, synaptic ultrastructure, and synapse maturation. We further demonstrate that LRP4 promotes most aspects of presynaptic development via a downstream SR-protein kinase, SRPK79D. SRPK79D overexpression suppresses synaptic defects associated with loss of lrp4. These data demonstrate a function for LRP4 as a peripheral synaptic organizer acting presynaptically, highlight a downstream mechanism conserved with its CNS function, and indicate previously unappreciated roles for LRP4 in cytoskeletal organization, synapse maturation, and active zone organization, underscoring its developmental importance.

Role of complement in myasthenia gravis

Myasthenia gravis is a prototypic neuroimmune disorder with autoantibodies targeting the acetylcholine receptor complex at the neuromuscular junction. Patients present with mainly ocular muscle weakness and tend to have a generalized muscle weakness later in the clinical course. The weakness can be severe and fatal when bulbar muscles are heavily involved. Acetylcholine receptor antibodies are present in the majority of patients and are of IgG1 and IgG3 subtypes which can activate the complement system. The complement involvement plays a major role in the neuromuscular junction damage and the supporting evidence in the literature is described in this article. Complement therapies were initially studied and approved for paroxysmal nocturnal hemoglobinuria and in the past decade, those have also been studied in myasthenia gravis. The currently available randomized control trial and real-world data on the efficacy and safety of the approved and investigational complement therapies are summarized in this review.

Myasthenia Gravis Presenting as Bulbar Palsy

Myasthenia gravis is a rare autoimmune condition that affects postsynaptic cholinergic receptors, resulting in symptoms of muscular fatigue. Clinical signs could be subtle and variable, often leading to many differentials. This leads to inappropriate tests being performed and a delay in diagnosis. Although ocular signs are more common, it may rarely present as bulbar palsy. Our patient, in her 30s, was referred to the emergency department after six months of symptom onset when she was discovered to be at a high risk of silent aspiration. Her presentation was predominantly bulbar palsy, but after appropriate tests, she was eventually diagnosed with generalized myasthenia gravis with a concurrent thymoma. Her treatment included pyridostigmine, corticosteroid, and immunoglobulins, while a thymectomy was scheduled as a planned procedure. Prompt diagnosis and timely management can reduce morbidity and mortality in such cases.

Myasthenia Gravis: Novel Findings and Perspectives on Traditional to Regenerative Therapeutic Interventions

The prevalence of myasthenia gravis (MG), an autoimmune disorder, is increasing among all subsets of the population leading to an elevated economic and social burden. The pathogenesis of MG is characterized by the synthesis of autoantibodies against the acetylcholine receptor (AChR), low-density lipoprotein receptor-related protein 4 (LRP4), or muscle-specific kinase at the neuromuscular junction, thereby leading to muscular weakness and fatigue. Based on clinical and laboratory examinations, the research is focused on distinguishing MG from other autoimmune, genetic diseases of neuromuscular transmission. Technological advancements in machine learning, a subset of artificial intelligence (AI) have been assistive in accurate diagnosis and management. Besides, addressing the clinical needs of MG patients is critical to improving quality of life (QoL) and satisfaction. Lifestyle changes including physical exercise and traditional Chinese medicine/herbs have also been shown to exert an ameliorative impact on MG progression. To achieve enhanced therapeutic efficacy, cholinesterase inhibitors, immunosuppressive drugs, and steroids in addition to plasma exchange therapy are widely recommended. Under surgical intervention, thymectomy is the only feasible alternative to removing thymoma to overcome thymoma-associated MG. Although these conventional and current therapeutic approaches are effective, the associated adverse events and surgical complexity limit their wide application. Moreover, Restivo et al. also, to increase survival and QoL, further recent developments revealed that antibody, gene, and regenerative therapies (such as stem cells and exosomes) are currently being investigated as a safer and more efficacious alternative. Considering these above-mentioned points, we have comprehensively reviewed the recent advances in pathological etiologies of MG including COVID-19, and its therapeutic management.

Global research hotspots and frontiers of myasthenia gravis from 2002 to 2021: A bibliometric study

The objective of this study is to utilize bibliometric and visual analysis techniques to identify hotspots and frontiers of research in myasthenia gravis (MG) and provide valuable references for future research. The Web of Science Core Collection (WoSCC) database was used to retrieve literature data related to MG research, which was then analyzed using VOSviewer 1.6.18, CiteSpace 6.1.R3, and the Online Platform for Bibliometric Analysis. The analysis revealed 6734 publications distributed across 1612 journals and contributed by as many as 24,024 authors affiliated with 4708 institutions across 107 countries/regions. The number of annual publications and citations for MG research has steadily increased over the past 2 decades, with the last 2 years alone witnessing a remarkable increase in annual publications and citations to over 600 and 17,000, respectively. In terms of productivity, the United States emerged as the top producing country, while the University of Oxford ranked first in terms of research institutions. Vincent A was identified as the top contributor in terms of publications and citations. Muscle & Nerve and Neurology ranked first in publications and citations respectively, with clinical neurology and neurosciences among the main subject categories explored. The study also identified pathogenesis, eculizumab, thymic epithelial cells, immune checkpoint inhibitors, thymectomy, MuSK antibodies, risk, diagnosis, and management as the current hot research topics in MG, while burst keywords like quality of life, immune-related adverse events (irAEs), rituximab, safety, nivolumab, cancer, and classification indicated the frontiers of MG research. This study effectively identifies the hotspots and frontiers of MG research, and offers valuable references for researchers interested in this area.

Clinicoserological insights into patients with immune checkpoint inhibitor-induced myasthenia gravis

To compare the immunopathology of immune checkpoint inhibitor-induced myasthenia gravis (ICI-MG) and idiopathic MG, we profiled the respective AChR autoantibody pathogenic properties. Of three ICI-MG patients with AChR autoantibodies, only one showed complement activation and modulation/blocking potency, resembling idiopathic MG. In contrast, AChR autoantibody-mediated effector functions were not detected in the other two patients, questioning the role of their AChR autoantibodies as key mediators of pathology. The contrasting properties of AChR autoantibodies in these cases challenge the accuracy of serological testing in establishing definite ICI-MG diagnoses and underscore the importance of a thorough clinical assessment when evaluating ICI-related adverse events.

DOK7 Promotes NMJ Regeneration After Nerve Injury

Motor function recovery from injury requires the regeneration of not only muscle fibers, but also the neuromuscular junction-the synapse between motor nerve terminals and muscle fibers. However, unlike muscle regeneration which has been extensively studied, little is known about the molecular mechanisms of NMJ regeneration. Recognizing the critical role of agrin-LRP4-MuSK signaling in NMJ formation and maintenance, we investigated whether increasing MuSK activity promotes NMJ regeneration. To this end, we evaluated the effect of DOK7, a protein that stimulates MuSK, on NMJ regeneration. Reinnervation, AChR cluster density, and endplate area were improved, and fragmentation was reduced in the AAV9-DOK7-GFP-injected muscles compared with muscles injected with AAV9-GFP. These results demonstrated expedited NMJ regeneration associated with increased DOK7 expression and support the hypothesis that increasing agrin signaling benefits motor function recovery after injury. Our findings propose a potentially new therapeutic strategy for functional recovery after muscle and nerve injury, i.e., promoting NMJ regeneration by increasing agrin signaling.

Autoantibody detection by a live cell-based assay in conventionally antibody-tested triple seronegative Myasthenia gravis

Autoantibody testing is the mainstay in confirming the diagnosis of autoimmune myasthenia gravis (MG). However, in approximately 15% of patients, antibody testing in clinical routine remains negative (seronegative MG). This study aimed at assessing the prevalence of "clustered" AChR- and MuSK- and LRP4- autoantibodies using a live cell-based assay in a large German cohort of seronegative myasthenia gravis (SNMG) patients. A total of 67 SNMG patients were included. Clustered AChR-ab were identified in 4.5% (n = 3) of patients. Two out of the three patients showed binding to the adult AchR as well as the fetal AchR. None of the patients was positive for MuSK- or LRP4-autoantibodies. There were no differences in clinical characteristics between the patients with and without clustered AChR-ab detection. Comparison of clinical data of our cohort with clinical data from the nationwide Myasthenia gravis registry showed broad similarities between seronegative MG patients of both cohorts.

Development and Application of a Cell-Based Assay for LRP4 Antibody Associated With Myasthenia Gravis

BACKGROUND AND PURPOSE

Among patients with double-seronegative myasthenia gravis (dSN-MG) who do not have detectable antibodies against acetylcholine receptor or muscle-specific tyrosine kinase, autoantibodies against low-density lipoprotein receptor-related protein 4 (LRP4-Ab) have been detected recently. The purpose of this study was to develop an in-house cell-based assay (CBA) to detect LRP4-Ab and to apply it to samples from patients with MG.

METHODS

The complementary DNA of LRP4 fused into a vector plasmid containing GFP was transfected into human embryonic kidney 293 (HEK293) cells. LRP4 expression in the transfected HEK293 cells was assessed using the reverse-transcription polymerase chain reaction (RT-PCR), Western blotting, and immunocytochemistry. The CBA included 252 sera collected from 202 patients with MG and 38 with other neuromuscular diseases, and 12 healthy controls. The transfected HEK293 cells were incubated using sera and antihuman immunoglobulin G antibodies conjugated with Alexa Fluor 594. The presence of LRP4-Ab was determined based on the fluorescence intensity and the localization in fluorescence microscopy.

RESULTS

The expressions of the mRNA and protein of LRP4 in the transfected HEK293 cells were confirmed using RT-PCR and Western blotting, respectively. Immunocytochemistry indicated LPR4 expression on the cell membrane. Among 202 patients with MG including 53 with dSN-MG, LRP4-Ab were positive in 3 patients who were all double seronegative. LRP4-Ab were not detected in the patients with other neuromuscular diseases or the healthy controls.

CONCLUSIONS

A CBA for detecting LRP4-Ab associated with MG has been developed, and was used to find LRP4-Ab in the sera of patients with MG.

Balancing WNT signalling in early forebrain development: The role of LRP4 as a modulator of LRP6 function

The specification of the forebrain relies on the precise regulation of WNT/ß-catenin signalling to support neuronal progenitor cell expansion, patterning, and morphogenesis. Imbalances in WNT signalling activity in the early neuroepithelium lead to congenital disorders, such as neural tube defects (NTDs). LDL receptor-related protein (LRP) family members, including the well-studied receptors LRP5 and LRP6, play critical roles in modulating WNT signalling capacity through tightly regulated interactions with their co-receptor Frizzled, WNT ligands, inhibitors and intracellular WNT pathway components. However, little is known about the function of LRP4 as a potential modulator of WNT signalling in the central nervous system. In this study, we investigated the role of LRP4 in the regulation of WNT signalling during early mouse forebrain development. Our results demonstrate that LRP4 can modulate LRP5- and LRP6-mediated WNT signalling in the developing forebrain prior to the onset of neurogenesis at embryonic stage 9.5 and is therefore essential for accurate neural tube morphogenesis. Specifically, LRP4 functions as a genetic modifier for impaired mitotic activity and forebrain hypoplasia, but not for NTDs in LRP6-deficient mutants. In vivo and in vitro data provide evidence that LRP4 is a key player in fine-tuning WNT signalling capacity and mitotic activity of mouse neuronal progenitors and of human retinal pigment epithelial (hTERT RPE-1) cells. Our data demonstrate the crucial roles of LRP4 and LRP6 in regulating WNT signalling and forebrain development and highlight the need to consider the interaction between different signalling pathways to understand the underlying mechanisms of disease. The findings have significant implications for our mechanistic understanding of how LRPs participate in controlling WNT signalling.

Reemergence of pathogenic, autoantibody-producing B cell clones in myasthenia gravis following B cell depletion therapy

Myasthenia gravis (MG) is an autoantibody-mediated autoimmune disorder of the neuromuscular junction. A small subset of patients (<10%) with MG, have autoantibodies targeting muscle-specific tyrosine kinase (MuSK). MuSK MG patients respond well to CD20-mediated B cell depletion therapy (BCDT); most achieve complete stable remission. However, relapse often occurs. To further understand the immunomechanisms underlying relapse, we studied autoantibody-producing B cells over the course of BCDT. We developed a fluorescently labeled antigen to enrich for MuSK-specific B cells, which was validated with a novel Nalm6 cell line engineered to express a human MuSK-specific B cell receptor. B cells (≅ 2.6 million) from 12 different samples collected from nine MuSK MG patients were screened for MuSK specificity. We successfully isolated two MuSK-specific IgG4 subclass-expressing plasmablasts from two of these patients, who were experiencing a relapse after a BCDT-induced remission. Human recombinant MuSK mAbs were then generated to validate binding specificity and characterize their molecular properties. Both mAbs were strong MuSK binders, they recognized the Ig1-like domain of MuSK, and showed pathogenic capacity when tested in an acetylcholine receptor (AChR) clustering assay. The presence of persistent clonal relatives of these MuSK-specific B cell clones was investigated through B cell receptor repertoire tracing of 63,977 unique clones derived from longitudinal samples collected from these two patients. Clonal variants were detected at multiple timepoints spanning more than five years and reemerged after BCDT-mediated remission, predating disease relapse by several months. These findings demonstrate that a reservoir of rare pathogenic MuSK autoantibody-expressing B cell clones survive BCDT and reemerge into circulation prior to manifestation of clinical relapse. Overall, this study provides both a mechanistic understanding of MuSK MG relapse and a valuable candidate biomarker for relapse prediction.

Novel pathophysiological insights in autoimmune myasthenia gravis

PURPOSE OF REVIEW

This review summarizes recent insights into the immunopathogenesis of autoimmune myasthenia gravis (MG). Mechanistic understanding is presented according to MG disease subtypes and by leveraging the knowledge gained through the use of immunomodulating biological therapeutics.

RECENT FINDINGS

The past two years of research on MG have led to a more accurate definition of the mechanisms through which muscle-specific tyrosine kinase (MuSK) autoantibodies induce pathology. Novel insights have also emerged from the collection of stronger evidence on the pathogenic capacity of low-density lipoprotein receptor-related protein 4 autoantibodies. Clinical observations have revealed a new MG phenotype triggered by cancer immunotherapy, but the underlying immunobiology remains undetermined. From a therapeutic perspective, MG patients can now benefit from a wider spectrum of treatment options. Such therapies have uncovered profound differences in clinical responses between and within the acetylcholine receptor and MuSK MG subtypes. Diverse mechanisms of immunopathology between the two subtypes, as well as qualitative nuances in the autoantibody repertoire of each patient, likely underpin the variability in therapeutic outcomes. Although predictive biomarkers of clinical response are lacking, these observations have ignited the development of assays that might assist clinicians in the choice of specific therapeutic strategies.

SUMMARY

Recent advances in the understanding of autoantibody functionalities are bringing neuroimmunologists closer to a more detailed appreciation of the mechanisms that govern MG pathology. Future investigations on the immunological heterogeneity among MG patients will be key to developing effective, individually tailored therapies.

Clinical Characteristics and Prognosis of Anti-AChR Positive Myasthenia Gravis Combined With Anti-LRP4 or Anti-Titin Antibody

Objective

This study aimed to summarize the clinical characteristics and prognosis of patients with anti- acetylcholine receptor (AChR) positive myasthenia gravis (MG) with a combination of anti-LRP4 or Titin antibodies.

Methods

A total of 188 patients with generalized MG before immunotherapy were retrospectively collected and then divided into three groups: single anti-AChR positive-MG (AChR-MG, 101 cases), anti-AChR combined with anti-low-density lipoprotein receptor-related protein four-positive MG (AChR+LRP4-MG, 29 cases), and anti-AChR combined with anti-Titin-positive MG (AChR+Titin-MG, 58 cases). Clinical manifestations, therapeutic responses to immunotherapy, and follow-up information were analyzed.

Results

Of the 188 seropositive MG patients, 29 (15.4%) were positive for both AChR and LRP4 antibodies, and 58 (30.9%) were positive for both AChR and Titin antibodies. The mean disease onset ages in the three groups were 47.41 ± 7.0, 49.81 ± 9.2, and 48.11 ± 6.5 years, respectively. AChR+LRP4-MG showed female predominance (27.6% were males and 72.4% were females), with mild overall clinical symptoms. The AChR+Titin-MG group showed shorter times for conversion to generalized MG (5.14 ± 0.0 months) than the AChR-MG group (11.69 ± 0.0 months) and the AChR+LRP4-MG group (13.08 ± 0.5 months; P < 0.001 in both cases). Furthermore, AChR+Titin-MG group had increased bulbar dysfunction, higher incidences of thymoma (32.8 vs. 19.8% and 3.4%, P=0.035), more severe quantitative MG scores, as assessed by both QMG scores [15.5 (11.75–22.5) vs. 13 (8–19), P = 0.005; and 9 (6–14) P < 0.001], and MG-ADL scores [10 (8–13) vs. 8 (5–13), P = 0.018; and 6 (4–8), P < 0.001]. Treatment for AChR+Titin-MG was largely dependent on corticosteroids and immunosuppressive agents (56.7 vs. 19.2% and 16.7%, p = 0.028). The rates of achieving s(MMS) or better within 2 years following immunotherapy in the three groups were 51.5, 62.1, and 51.7%, respectively (P = 0.581).

Conclusion

Clinical symptoms of anti-AChR positive MG combined with Titin antibody were more severe and progressed faster than those in the AChR + LRP4 and AChR groups. Regardless of antibody status, all patients responded well to immunotherapy and had relatively good prognoses.

Myasthenia gravis in clinical practice

BACKGROUND

Myasthenia gravis is largely a treatable disease, but it can result in significant morbidity and even mortality, which can usually be avoided, or at least mitigated, with timely diagnosis and appropriate treatment of the disease. Objective: this review aims to summarize the main practical aspects of the diagnostic approach, treatment and care of myasthenic patients.

METHODS

The authors performed a non-systematic critical review summarizing the main practical aspects of myasthenia gravis.

RESULTS

Most patients with myasthenia have autoantibodies targeted at acetylcholine receptors or, less commonly, muscle-specific kinase - MuSK. Electrophysiology plays an important role in the diagnosis of neuromuscular junction dysfunction. The central clinical manifestation of myasthenia gravis is fatigable muscle weakness, which can affect eye, bulbar, respiratory, and limb muscles. With rare exceptions, patients have a good response to symptomatic treatment, but corticosteroids and/or immunosuppressants are usually also necessary to obtain good control of the manifestations of the disease.

CONCLUSION

Knowledge of the peculiar aspects of their clinical and electrophysiological presentations is important for the diagnosis. Likewise, specific treatment and response time to each drug are crucial for proper care.

Impaired signaling for neuromuscular synaptic maintenance is a feature of Motor Neuron Disease

A central event in the pathogenesis of motor neuron disease (MND) is the loss of neuromuscular junctions (NMJs), yet the mechanisms that lead to this event in MND remain to be fully elucidated. Maintenance of the NMJ relies upon neural agrin (n-agrin) which, when released from the nerve terminal, activates the postsynaptic Muscle Specific Kinase (MuSK) signaling complex to stabilize clusters of acetylcholine receptors. Here, we report that muscle from MND patients has an increased proportion of slow fibers and muscle fibers with smaller diameter. Muscle cells cultured from MND biopsies failed to form large clusters of acetylcholine receptors in response to either non-MND human motor axons or n-agrin. Furthermore, levels of expression of MuSK, and MuSK-complex components: LRP4, Caveolin-3, and Dok7 differed between muscle cells cultured from MND patients compared to those from non-MND controls. To our knowledge, this is the first time a fault in the n-agrin-LRP4-MuSK signaling pathway has been identified in muscle from MND patients. Our results highlight the n-agrin-LRP4-MuSK signaling pathway as a potential therapeutic target to prolong muscle function in MND.

Novel treatment strategies for acetylcholine receptor antibody-positive myasthenia gravis and related disorders

The presence of autoantibodies directed against the muscle nicotinic acetylcholine receptor (AChR) is the most common cause of myasthenia gravis (MG). These antibodies damage the postsynaptic membrane of the neuromuscular junction and cause muscle weakness by depleting AChRs and thus impairing synaptic transmission. As one of the best-characterized antibody-mediated autoimmune diseases, AChR-MG has often served as a reference model for other autoimmune disorders. Classical pharmacological treatments, including broad-spectrum immunosuppressive drugs, are effective in many patients. However, complete remission cannot be achieved in all patients, and 10% of patients do not respond to currently used therapies. This may be attributed to production of autoantibodies by long-lived plasma cells which are resistant to conventional immunosuppressive drugs. Hence, novel therapies specifically targeting plasma cells might be a suitable therapeutic approach for selected patients. Additionally, in order to reduce side effects of broad-spectrum immunosuppression, targeted immunotherapies and symptomatic treatments will be required. This review presents established therapies as well as novel therapeutic approaches for MG and related conditions, with a focus on AChR-MG.

Analysis of nAChR Autoantibodies Against Extracellular Epitopes in MG Patients

Myasthenia gravis (MG) is an autoimmune disorder caused by autoantibodies targeting components of the postsynaptic membrane of the neuromuscular junction (NMJ), leading to neuromuscular transmission deficiency. In the vast majority of patients, these autoantibodies target the nicotinic acetylcholine receptor (nAChR), a heteropentameric ion channel anchored to the postsynaptic membrane of the NMJ. Autoantibodies in patients with MG may target all the subunits of the receptor at both their extracellular and intracellular regions. Here, we combine immunoadsorption with a cell-based assay to examine the specificity of the patients' autoantibodies against the extracellular part of the nAChR. Our results reveal that these autoantibodies can be divided into distinct groups, based on their target, with probably different impacts on disease severity. Although our findings are based on a small sample group of patients, they strongly support that additional analysis of the specificity of the autoantibodies of patients with MG could serve as a valuable tool for the clinicians' decision on the treatment strategy to be followed.

Bedside and laboratory diagnostic testing in myasthenia

Myasthenia gravis (MG) and congenital myasthenic syndromes (CMS) are a group of disorders with a well characterised autoimmune or genetic and neurophysiological basis. We reviewed the literature from the last 20 years assessing the utility of various neurophysiological, immunological, provocative and genetic tests in MG and CMS. Diagnostic sensitivity of repetitive nerve stimulation test ranges between 14 and 94% and specificity between 73 and 100%; sensitivity of single-fibre EMG (SFEMG) test ranges between 64 and 100% and specificity between 22 and 100%; anti-acetylcholine receptor (AChR) antibody sensitivity ranges from 13 to 97% and specificity ranges from 95 to 100%. Overall, SFEMG has the highest sensitivity while positive anti-AChR antibodies have the highest specificity. Newer testing strategies that have been investigated over the last couple of decades include ocular vestibular-evoked myogenic potentials, otoacoustic emissions and disease-specific circulating miRNAs in serum for autoimmune myasthenia, as well as next-generation sequencing for genetic testing of CMS. While there has been significant progress in developing newer testing strategies for diagnosing MG and CMS over the last couple of decades, more research is needed to assess the utility of these newer tools regarding their sensitivity and specificity.

Efficacy and Safety of Low-Dose Rituximab in Anti-MuSK Myasthenia Gravis Patients: A Retrospective Study

PURPOSE

To evaluate the efficacy and safety of low dosages of rituximab (RTX) in the treatment of MuSK-antibody-positive MG patients.

PATIENTS AND METHODS

We retrospectively analyzed the data of MuSK-antibody-positive MG patients who were treated with low dosages of RTX from January 2018 to October 2021. The long-term treatment response to RTX was assessed by Myasthenia Gravis Foundation of America (MGFA) post-interventional status (PIS), Myasthenia Gravis Status and Treatment Intensity (MGSTI), dosage of steroid, MG-related activities of daily living (MG-ADL) and myasthenic muscle score (MMS) at the end of follow-up.

RESULTS

Clinical improvement was observed in all eight patients with follow-up for 8 to 29 months after treatment. At the last visit, complete stable remission had been achieved in one patient, pharmacologic remission in three patients, minimal manifestations status in three patients and improved in one patient based on the MGFA-PIS criteria. MGSTI level 2 or better had been reached in six (75%) patients at the last visit. The steroid dosage decreased from 60 mg at baseline to 15 mg at the last follow-up (p = 0.011). The average MG-ADL score decreased from 11 (range 7 to 15) to 0 (range 0 to 3; p = 0.011), and the MMS improved from 38.5 (range 24 to 60) to 100 (range 90 to 100; p = 0.012). These differences were all statistically significant. During RTX treatment and subsequent follow-up, 1 patient reported minor post-infusion malaise.

CONCLUSION

Low-dose RTX is effective and safe for treating anti-MuSK antibody positive MG patients. A long-term response is observed after treatment. Larger prospective studies are required to provide further evidence.

A Review on the Role of Non-Coding RNAs in the Pathogenesis of Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune condition related to autoantibodies against certain proteins in the postsynaptic membranes in the neuromuscular junction. This disorder has a multifactorial inheritance. The connection between environmental and genetic factors can be established by epigenetic factors, such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). XLOC_003810, SNHG16, IFNG-AS1, and MALAT-1 are among the lncRNAs with a possible role in the pathoetiology of MG. Moreover, miR-150-5p, miR-155, miR-146a-5p, miR-20b, miR-21-5p, miR-126, let-7a-5p, and let-7f-5p are among miRNAs whose roles in the pathogenesis of MG has been assessed. In the current review, we summarize the impact of miRNAs and lncRNAs in the development or progression of MG.

Comparative Analysis of BIOCHIP Mosaic-Based Indirect Immunofluorescence with Enzyme-Linked Immunosorbent Assay for Diagnosing Myasthenia Gravis

Background: The detection of anti-acetylcholine receptor (AChR) and anti-muscle-specific tyrosine kinase (MuSK) antibodies is useful in myasthenia gravis (MG) diagnosis and management. BIOCHIP mosaic-based indirect immunofluorescence is a novel analytical method, which employs the simultaneous detection of anti-AChR and anti-MuSK antibodies in a single miniature incubation field. In this study, we compare, for the first time, the BIOCHIP MG mosaic with conventional enzyme-linked immunosorbent assay (ELISA) in the diagnosis of MG. Methods: A total of 71 patients with MG diagnosis were included in the study. Anti-AChR and anti-MuSK antibodies were measured separately by two different ELISA and simultaneously by BIOCHIP. The results were then compared. Results: The overall concordance between ELISA and BIOCHIP for anti-AChR reactivity was 74%. Cohen’s kappa was 0.51 (95% CI 0.32–0.71), which corresponds to 90% of the maximum possible kappa (0.57), given the observed marginal frequencies. The overall concordance for anti-MuSK reactivity was 84%. Cohen’s kappa was 0.11 (95% CI 0.00–0.36), which corresponds to 41% of the maximum possible kappa (0.27). Conclusion: The overall concordance among assays is not optimal.

Congenital myasthenic syndromes: where do we go from here?

Congenital myasthenia syndromes are rare but often treatable conditions affecting neuromuscular transmission. They result from loss or impaired function of one of a number of proteins secondary to a genetic defect. An estimate of the prevalence in the UK gave 9.2 cases per million, however, this is likely an underestimate since the adoption of next generation sequencing for diagnosis away from specialist centres is enhancing the 'pick up' rate. Next generation sequencing has helped identify a series of novel genes that harbour mutations causative for congenital myasthenic syndrome that include not only genes that encode proteins specifically expressed at the neuromuscular junction but also those that are ubiquitously expressed. The list of genes harbouring disease-causing mutations for congenital myasthenic syndrome continues to expand and is now over 30, but with many of the newly identified genes it is increasingly being recognised that abnormal neuromuscular transmission is only one component of a multifaceted phenotype in which muscle, the central nervous system, and other organs may also be affected. Treatment can be tailored to the underlying molecular mechanism for impaired neuromuscular transmission but treating the more complex multifaceted disorders and will require development of new therapies.

Characterization of LRP4/Agrin Antibodies From a Patient With Myasthenia Gravis

BACKGROUND AND OBJECTIVE

To determine whether human anti-LRP4/agrin antibodies are pathogenic in mice and to investigate underpinning pathogenic mechanisms.

METHODS

Immunoglobulin (Ig) was purified from a patient with myasthenia gravis (MG) with anti-LRP4/agrin antibodies and transferred to mice. Mice were characterized for body weight, muscle strength, twitch and tetanic force, neuromuscular junction (NMJ) functions including compound muscle action potential (CMAP) and endplate potentials, and NMJ structure. Effects of the antibodies on agrin-elicited muscle-specific tyrosine kinase (MuSK) activation and AChR clustering were studied and the epitopes of these antibodies were identified.

RESULTS

Patient Ig-injected mice had MG symptoms, including weight loss and muscle weakness. Decreased CMAPs, reduced twitch and tetanus force, compromised neuromuscular transmission, and NMJ fragmentation and distortion were detected in patient Ig-injected mice. Patient Ig inhibited agrin-elicited MuSK activation and AChR clustering. The patient Ig recognized the β3 domain of LRP4 and the C-terminus of agrin and reduced agrin-enhanced LRP4-MuSK interaction.

DISCUSSION

Anti-LRP4/agrin antibodies in the patient with MG is pathogenic. It impairs the NMJ by interrupting agrin-dependent LRP4-MuSK interaction.

Suppression of the CD28/B7 pathway reduces the occurrence and development of myasthenia gravis and cytokine levels

BACKGROUND

Myasthenia gravis (MG) is an antibody-mediated, autoimmune neuromuscular disease. Reports have indicated that the CD28/B7 ligand interactions play a crucial role during primary immune responses. Hence, the aim of the present study was to investigate the possible effects of the CD28/B7 pathway on the occurrence and development of MG and its associated cytokine factors.

METHODS

An experimental autoimmune myasthenia gravis (EAMG) was initially established by immunization of Lewis rats with acetylcholine receptor (AChR) α97-116 peptide. Then the rats were treated with dexamethasone and CTLA4-Ig (used for inhibiting the CD28/B7 pathway). Serum levels of AChR IgG and AChR IgG2b were then detected using ELISA. The clinical features, muscle contraction function, AChR content, expression of CD28, CTLA4, B7.1 and B7.2 in mononuclear cells of peripheral blood and the secretion of cytokines (INF-γ, IL-2, IL-10 and IL-12) in serum of rats were measured. Finally, lymphocyte proliferation upon CTLA4 IgG treatment was examined in vitro.

RESULTS

Inhibition of the CD28/B7 pathway and dexamethasone were found to significantly improve clinical symptoms of EAMG rats, reduce serum levels of AChR IgG, AChR IgG2b, INF-γ, IL-2, IL-10 and IL-12, the expression of CD28, CTLA4, B7.1 and B7.2 in mononuclear cells of peripheral blood, and enhance muscle contraction function and AChR content in the muscle in vivo. Meanwhile, CTLA4 IgG could abolish the increased lymphocyte proliferation following AChR stimulation in vitro.

CONCLUSION

Overall, the suppression of the CD28/B7 pathway by CTLA4-Ig can have the potential to retard the occurrence and development of MG.

Harmony Lost: Cell-Cell Communication at the Neuromuscular Junction in Motor Neuron Disease

The neuromuscular junction (NMJ) is a specialized synapse that is the point of connection between motor neurons and skeletal muscle. Although developmental studies have established the importance of cell-cell communication at the NMJ for the integrity and full functionality of this synapse, the contribution of this structure as a primary driver in motor neuron disease pathogenesis remains uncertain. Here, we consider the biology of the NMJ and review emerging lines of investigation that are highlighting the importance of cell-cell interaction at the NMJ in spinal muscular atrophy (SMA), X-linked spinal and bulbar muscular atrophy (SBMA), and amyotrophic lateral sclerosis (ALS). Ongoing research may reveal NMJ targets and pathways whose therapeutic modulation will help slow the progression of motor neuron disease, offering a novel treatment paradigm for ALS, SBMA, SMA, and related disorders.

A Stable Cell Line Expressing Clustered AChR: A Novel Cell-Based Assay for Anti-AChR Antibody Detection in Myasthenia Gravis

Cell-based assays (CBAs) and radioimmunoprecipitation assay (RIPA) are the most sensitive methods for identifying anti-acetylcholine receptor (AChR) antibody in myasthenia gravis (MG). But CBAs are limited in clinical practice by transient transfection. We established a stable cell line (KL525) expressing clustered AChR by infecting HEK 293T cells with dual lentiviral vectors expressing the genes encoding the human AChR α1, β1, δ, ϵ and the clustering protein rapsyn. We verified the stable expression of human clustered AChR by immunofluorescence, immunoblotting, and real-time PCR. Fluorescence-activated cell sorting (FACS) was used to detect anti-AChR antibodies in 103 MG patients and 58 healthy individuals. The positive results of MG patients reported by the KL525 was 80.6% (83/103), 29.1% higher than the 51.4% (53/103) of RIPA. 58 healthy individuals tested by both the KL525 CBA and RIPA were all negative. In summary, the stable expression of clustered AChR in our cell line makes it highly sensitive and advantageous for broad clinical application in CBAs.

No correlation between acetylcholine receptor antibody concentration and individual clinical symptoms of myasthenia gravis: A systematic retrospective study involving 67 patients

OBJECTIVE

To investigate the correlation between acetylcholine receptor antibodies (AChR-Ab) concentration levels and individualized clinical symptoms in patients with AChR myasthenia gravis (AChR-MG) in China.

METHODS

ELISA was used to determine the concentration of AChR-Ab in patients with MG. The Myasthenia Gravis Foundation of America (MGFA) Clinical Classification, Quantitative Myasthenia Gravis (QMG) score, and MG-specific activities of daily living (MG-ADL) scoring systems were used to evaluate the clinical status of patients. Spearman correlation analysis was used to determine the correlation between the AChR-Ab concentration and clinical score. The changes in the antibody concentration and clinical score are shown in MGFA-antibody concentration-treatment plots.

RESULTS

Autoantibody detection tests were performed in 67 patients, and their clinical scores were recorded. Forty-nine patients received immunosuppressive therapy, 17 patients received pyridostigmine only, and 1 patient under thymectomy without any medication. The AChR-Ab concentration correlated with the MGFA Classification in 5 (29.4%) patients in the pyridostigmine-only group and 15 (30.6%) patients in the immunosuppressive drug group. The changes in the MGFA Classification preceded the changes in the AChR-Ab concentration in 4 (23.5%) patients treated with pyridostigmine and 10 (20.4%) patients on immunosuppressive drugs. In patients on oral non-steroidal immunosuppressants, the AChR-Ab concentration changed by more than 50%, whereas the MGFA Classification did not increase. The AChR-Ab concentration decreased in 17/32 (53.1%) patients after thymectomy, and then increased, whereas the AChR-Ab concentration increased in 15/32 (46.9%) patients and the MGFA Classification decreased in 27/32 (81.8%) patients after thymectomy. The AChR-Ab concentration presented a slight correlation with the corresponding MGFA, QMG, and MG-ADL in patients with thymoma.

DISCUSSION

In the Chinese AChR-MG population, the Changes in the AChR-Ab concentration in individuals with AChR-MG did not consistently correlate with the severity of clinical symptoms.

Heterogeneity in myasthenia gravis: considerations for disease management

Introduction: Myasthenia gravis is a rare disease of the neuromuscular junction and a prototype of B cell-driven immunopathology. Pathogenic antibodies target post-synaptic transmembrane proteins, most commonly the nicotinic acetylcholine receptor and the muscle-specific tyrosine kinase, inducing end-plate alterations and neuromuscular transmission impairment. Several clinical subtypes are distinct on the basis of associated antibodies, age at symptom onset, thymus pathology, genetic factors, and weakness distribution. These subtypes have distinct pathogenesis that can account for different responses to treatment. Conventional therapy is based on the use of symptomatic agents, steroids, immunosuppressants and thymectomy. Of late, biologics have emerged as effective therapeutic options.Areas covered: In this review, we will discuss the management of myasthenia gravis in relation to its phenotypic and biological heterogeneity, in the light of recent advances in the disease immunopathology, new diagnostic tools, and results of clinical trialsExpert opinion: Clinical management is shaped on serological subtype, and patient age at onset, lifestyle and comorbidities, balancing therapeutic needs and safety. Although reliable biomarkers predictive of clinical and biologic outcome are still lacking, recent developments promise a more effective and safe treatment. Disease subtyping according to serological testing and immunopathology is crucial to the appropriateness of clinical management.

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.

Improving laboratory diagnostics in myasthenia gravis

Introduction: Myasthenia gravis (MG) is a prototypical autoimmune disease, characterized by pathogenic autoantibodies targeting structures of the neuromuscular junction. Radioimmunoprecipitation assays (RIPAs) represent the gold standard for their detection. However, new methods are emerging to complement, or overcome RIPAs, also with the perspective of eliminating the use of radioactive reagents.Areas covered: We discuss advances in laboratory methods, prompted especially by cell-based assays (CBAs), for the detection of the autoantibodies of MG diagnostics, above all those to the nicotinic acetylcholine receptor (AChR), muscle-specific kinase (MuSK), and low molecular-weight receptor-related low-density lipoprotein-4 (LRP4).Expert opinion: CBA technology makes AChRs aggregate on cell membranes, thus allowing to detect autoantibodies to clustered AChRs, with reduction of seronegative MG cases. The diagnostic relevance of RIPA/CBA-measurable LRP4 antibodies is still unclear, in Caucasian patients at least. Live CBAs for the detection of AChR, MuSK, and LRP4 antibodies might represent an alternative to RIPAs, but first require full validation. CBAs could be used as screening tests, limiting RIPAs for antibody quantification. To this end, ELISAs might be an alternative.Fixation procedures preserving enough degree of antigen conformationality could yield AChR and MuSK CBAs suitable for a wide use in clinical-chemistry laboratories.

Neuromuscular junction-specific genes screening by deep RNA-seq analysis

Background

Neuromuscular junctions (NMJs) are chemical synapses formed between motor neurons and skeletal muscle fibers and are essential for controlling muscle contraction. NMJ dysfunction causes motor disorders, muscle wasting, and even breathing difficulties. Increasing evidence suggests that many NMJ disorders are closely related to alterations in specific gene products that are highly concentrated in the synaptic region of the muscle. However, many of these proteins are still undiscovered. Thus, screening for NMJ-specific proteins is essential for studying NMJ and the pathogenesis of NMJ diseases.

Results

In this study, synaptic regions (SRs) and nonsynaptic regions (NSRs) of diaphragm samples from newborn (P0) and adult (3-month-old) mice were used for RNA-seq. A total of 92 and 182 genes were identified as differentially expressed between the SR and NSR in newborn and adult mice, respectively. Meanwhile, a total of 1563 genes were identified as differentially expressed between the newborn SR and adult SR. Gene Ontology (GO) enrichment analyses, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and gene set enrichment analysis (GSEA) of the DEGs were performed. Protein–protein interaction (PPI) networks were constructed using STRING and Cytoscape. Further analysis identified some novel proteins and pathways that may be important for NMJ development, maintenance and maturation. Specifically, Sv2b, Ptgir, Gabrb3, P2rx3, Dlgap1 and Rims1 may play roles in NMJ development. Hcn1 may localize to the muscle membrane to regulate NMJ maintenance. Trim63, Fbxo32 and several Asb family proteins may regulate muscle developmental-related processes.

Conclusion

Here, we present a complete dataset describing the spatiotemporal transcriptome changes in synaptic genes and important synaptic pathways. The neuronal projection-related pathway, ion channel activity and neuroactive ligand-receptor interaction pathway are important for NMJ development. The myelination and voltage-gated ion channel activity pathway may be important for NMJ maintenance. These data will facilitate the understanding of the molecular mechanisms underlying the development and maintenance of NMJ and the pathogenesis of NMJ disorders.

Autoantibodies to cortactin and agrin in sera of patients with myasthenia gravis

Autoantibodies against agrin and cortactin have been described in patients with myasthenia gravis. To further validate and characterize these autoantibodies, sera and/or plasma exchange material of 135 patients with myasthenia gravis were screened for anti-agrin or anti-cortactin autoantibodies. Autoantibodies against cortactin were detected in three patients and two controls and could be confirmed by cell-based assays using cortactin-transfected human embryonic kidney cells in both controls and one patient, but were not detectable in follow-up sera of the three patients. We did not detect any autoantibodies against agrin. The clinical phenotype of anti-cortactin-positive patients varied, arguing against a relevant pathogenic role.

Conservation and Innovation: Versatile Roles for LRP4 in Nervous System Development

As the nervous system develops, connections between neurons must form to enable efficient communication. This complex process of synaptic development requires the coordination of a series of intricate mechanisms between partner neurons to ensure pre- and postsynaptic differentiation. Many of these mechanisms employ transsynaptic signaling via essential secreted factors and cell surface receptors to promote each step of synaptic development. One such cell surface receptor, LRP4, has emerged as a synaptic organizer, playing a critical role in conveying extracellular signals to initiate diverse intracellular events during development. To date, LRP4 is largely known for its role in development of the mammalian neuromuscular junction, where it functions as a receptor for the synaptogenic signal Agrin to regulate synapse development. Recently however, LRP4 has emerged as a synapse organizer in the brain, where new functions for the protein continue to arise, adding further complexity to its already versatile roles. Additional findings indicate that LRP4 plays a role in disorders of the nervous system, including myasthenia gravis, amyotrophic lateral sclerosis, and Alzheimer's disease, demonstrating the need for further study to understand disease etiology. This review will highlight our current knowledge of how LRP4 functions in the nervous system, focusing on the diverse developmental roles and different modes this essential cell surface protein uses to ensure the formation of robust synaptic connections.

Serum Biomarkers in Neuro-Ophthalmology: When to Test

Discovery and characterization of serologic biomarkers has revolutionized the diagnostic framework of systemic and paraneoplastic autoimmune neuro-ophthalmic diseases. Expanding recognition of the multiple ocular and visual manifestations of these conditions highlights the important role of the referring provider in identifying potential cases. Increasing ease of access to serologic testing also enables these practitioners to initiate the diagnostic work-up in suspected cases. We aimed to provide an update on the current knowledge surrounding and use of relevant autoimmune biomarkers by correlating specific clinical neuro-ophthalmic manifestations with autoantibody biomarkers. The utility of select biomarkers for myasthenia gravis, neuromyelitis optica spectrum disorder, myelin oligodendrocyte glycoprotein-IgG-associated disorder, opsoclonus-myoclonus syndrome, anti-collapsin-response mediator protein-5 optic neuropathy, and glial fibrillary acidic protein-IgG-associated disease are discussed with particular focus on the clinical contexts in which to consider testing.

Anti-MuSK Positive Myasthenia Gravis with Anti-Lrp4 and Anti-titin Antibodies

In addition to muscle nicotinic acetylcholine receptor (AChR) and muscle-specific kinase (MuSK), low-density lipoprotein receptor (Lrp4) has recently been discovered to be a novel target antigen among patients with seronegative myasthenia gravis (MG). We herein report the findings of a 62-year-old patient who showed positivity for anti-MuSK, anti-Lrp4, and anti-titin antibodies. The patient developed MG crisis following a 10-year history of intermittent double vision with ptosis, and a 7-year history of dropped head. Our detailed clinical, laboratory, and therapeutic descriptions highlight its unique characteristics of anti-MuSK-antibody positive MG accompanied by anti-Lrp4 and anti-titin antibodies.