A network of core and subtype-specific gene expression programs in myositis

A neuromuscular clinician's primer on machine learning

Artificial intelligence is the future of clinical practice and is increasingly utilized in medical management and clinical research. The release of ChatGPT3 in 2022 brought generative AI to the headlines and rekindled public interest in software agents that would complete repetitive tasks and save time. Artificial intelligence/machine learning underlies applications and devices which are assisting clinicians in the diagnosis, monitoring, formulation of prognosis, and treatment of patients with a spectrum of neuromuscular diseases. However, these applications have remained in the research sphere, and neurologists as a specialty are running the risk of falling behind other clinical specialties which are quicker to embrace these new technologies. While there are many comprehensive reviews on the use of artificial intelligence/machine learning in medicine, our aim is to provide a simple and practical primer to educate clinicians on the basics of machine learning. This will help clinicians specializing in neuromuscular and electrodiagnostic medicine to understand machine learning applications in nerve and muscle ultrasound, MRI imaging, electrical impendence myography, nerve conductions and electromyography and clinical cohort studies, and the limitations, pitfalls, regulatory and ethical concerns, and future directions. The question is not whether artificial intelligence/machine learning will change clinical practice, but when and how. How future neurologists will look back upon this period of transition will be determined not by how much changed or by how fast clinicians embraced this change but by how much patient outcomes were improved.

The role of monocytes and macrophages in idiopathic inflammatory myopathies: insights into pathogenesis and potential targets

Idiopathic inflammatory myopathies (IIMs) are heterogeneous autoimmune disorders characterized by muscle inflammation, weakness, and extramuscular manifestations such as interstitial lung disease, skin rash, arthritis, dysphagia, myocarditis and other systemic organ involvement. Although T and B cells have historically been central to the understanding of IIM immunopathology, monocytes and their differentiated progenitor cells, macrophages, are increasingly being recognized as critical mediators of both tissue damage and repair. In subtypes such as dermatomyositis, immune-mediated necrotizing myopathy and antisynthetase syndrome, macrophages infiltrate skeletal muscle and other affected tissues, contributing to inflammation via production of pro-inflammatory cytokines, chemokines, and reactive oxygen species. Dysregulated interferon signaling, mitochondrial stress, and aberrant metabolic states in these cells further perpetuate tissue injury in IIMs. Conversely, certain macrophage subsets can support muscle fiber regeneration and dampen inflammation, underscoring the dual roles these cells can play. Future research into the heterogeneity of monocytes and macrophages, including single-cell transcriptomic and metabolomic approaches, will help clarify disease mechanisms, identify biomarkers of disease activity and prognosis, and guide novel therapeutic strategies targeting these innate immune cells in IIM.

Enhanced systemic oxidative stress response in patients with idiopathic inflammatory myopathies

BACKGROUND

Idiopathic inflammatory myopathies (IIM) are characterized by chronic inflammation, endothelial dysfunction, and muscle tissue mitochondrial defect, leading to the local oxidative stress response. However, data on its systemic intensity and correlation with IIM clinical and laboratory characteristics remains scarce.

METHODS

In clinically stable dermatomyositis (n = 18) and myositis (n = 38) patients and matched controls (n = 50), we measured global oxidative stress response in peripheral blood using a novel coumarin boronic acid (CBA) assay enabling real-time detection of protein hydroperoxides (HP) formed in serum.

RESULTS

We documented 36% faster kinetics (p < 0.001) and a 68% increase in the cumulative (p = 0.003) fluorescent product generation in the IIM group compared to the control, which indicates higher HP formation associated with systemic oxidative stress. The dynamics of fluorescent product growth were similar in the dermatomyositis and myositis groups. Interestingly, myositis patients with a marked increase in HP formation were characterized by lower serum myoglobin levels (p = 0.038). There was also an inverse correlation between serum myoglobin and the kinetics of HP formation (e.g., for cumulative in-time generation r = -0.35, p = 0.03). The systemic oxidative stress response measures were not related to clinical characteristics of the disease and treatment, internal medicine comorbidities, smoking status, or autoantibody profile.

CONCLUSIONS

IIM are characterized by a global pro-oxidant imbalance reflected by enhanced HP generation in serum. Furthermore, muscle weakening without active signs of muscle damage may be related to the increased local and systemic oxidative stress response, suggesting non-inflammatory pathomechanism of the disease that our technically undemanding assay may evaluate.

Experimental myositis: an optimised version of C-protein-induced myositis

INTRODUCTION

Inflammatory myopathies (IM) are a group of severe autoimmune diseases, sharing some similarities, whose cause is unknown and treatment is empirical.While C-protein-induced myositis (CIM), the most currently used mouse model of IM, has removed some roadblocks to understand and improve the treatment of IM, it has only been partially characterised and its generation limited by poor reproducibility. This study aimed at optimising the generation and the characterisation of CIM.

METHODS

In silico analysis was run to identify the top three specific and immunogenic regions of C-protein. The cognate polypeptides were synthesised and used to immunise C57BL/6N mice. Grip strength, walking ability, serum creatine kinase levels and muscle pathology (histological and electron microscopic features) were assessed. Immune cell proportions and interferon signature in muscles were also determined.

RESULTS

Among the three C-protein polypeptides with the highest immunogenic score, immunisation with the amino acids 965-991 induced the most severe phenotype (experimental myositis (EM)) characterised by 37% decrease in strength, 36% increase in hind base width, 45% increase in serum creatine-kinase level and 80% increase in histological inflammatory score. Optical and electron microscopy revealed mononuclear cell infiltrate, myofibre necrosis, atrophy, major histocompatibility complex-I expression as well as sarcolemmal, sarcomeric and mitochondrial abnormalities. Autoantibodies targeting C-protein, proinflammatory T-lymphocytes, macrophages, and type I and II interferon-stimulated transcripts were detected within the muscle of EM mice.

CONCLUSION

EM recapitulates the common hallmarks of IM. This costless, high throughput, reproducible and robust model, generated in the most commonly used background for genetically engineered mice, may foster preclinical research in IM.

Distinct Cytokine and Cytokine Receptor Expression Patterns Characterize Different Forms of Myositis

Objective

Myositis is a heterogeneous family of inflammatory myopathies. We sought to define the differential expression of cytokines, cytokine receptors, and immune checkpoint genes in muscle biopsies from patients with different forms of myositis in order to characterize patterns of inflammation in each.

Methods

Bulk RNA sequencing was performed on muscle biopsy samples from 669 patients, including 105 with dermatomyositis, 80 with immune-mediated necrotizing myopathy (IMNM), 65 with anti-synthetase syndrome, 53 with inclusion body myositis (IBM), 19 with anti-PM/Scl myositis, 310 with other inflammatory or genetic myopathies, and 37 controls with normal tissue (NT). Myositis clinical groups and autoantibody subgroups were analyzed separately. Expression data was analyzed for 338 genes encoding cytokines, cytokine receptors, and immune checkpoints. Myositis group-specific genes were identified from this list by finding genes that were specifically differentially expressed in one group compared to all samples and compared to NT (α<0.001).

Results

IBM patients had the most differentially overexpressed genes (71) among all clinical groups, including 37 that were IBM-specific. Among the top genes were several involved in type 1 inflammation, including CCL5, CXCR3, CCR5, CXCL9, and IFNG. Anti-Jo1 and anti-PM/Scl patients exhibited differential overexpression of a similar set of genes, while dermatomyositis patients exhibited differential overexpression of a different set of genes involved in type 1 inflammation. IMNM patients had the least number of differentially overexpressed genes with no predominant inflammatory pattern.

Conclusion

Each myositis clinical group and autoantibody subgroup had differentially overexpressed inflammatory mediators, including a strong type 1 inflammatory gene signature in IBM.

Recent Updates on the Pathogenesis of Inflammatory Myopathies

PURPOSE OF REVIEW

This review aims to provide a comprehensive and updated overview of autoimmune myopathies, with a special focus on the latest advancements in understanding the role of autoantibodies. We will begin by examining the risk factors and triggers associated with myositis. Next, we will delve into recent research on how autoantibodies contribute to disease pathogenesis. Finally, we will explore the latest innovations in treatment strategies and their implications for our understanding of myositis pathogenesis.

RECENT FINDINGS

Recent research has revealed that myositis-specific autoantibodies can infiltrate muscle cells and disrupt the function of their target autoantigens, playing a crucial role in disease pathogenesis. Significant advances in treatment include CD19 CAR-T cell therapy, JAK-STAT inhibitors, and novel strategies targeting the type 1 interferon pathway in dermatomyositis. Additionally, the ineffectiveness of complement inhibitors in treating immune-mediated necrotizing myositis has challenged established views on disease mechanisms. Autoimmune myopathies are a collection of disorders significantly influenced by specific autoantibodies that drive disease pathogenesis. This review highlights the critical role of autoantibody research in deepening our understanding of these conditions and discusses recent therapeutic advancements targeting key pathogenic pathways.

Pathological autoantibody internalisation in myositis

OBJECTIVES

Autoantibodies targeting intracellular proteins are common in various autoimmune diseases. In the context of myositis, the pathologic significance of these autoantibodies has been questioned due to the assumption that autoantibodies cannot enter living muscle cells. This study aims to investigate the validity of this assumption.

METHODS

Confocal immunofluorescence microscopy was employed to localise antibodies and other proteins of interest in myositis muscle biopsies. Bulk RNA sequencing was used to examine the transcriptomic profiles of 669 samples, including those from patients with myositis, disease controls and healthy controls. Additionally, antibodies from myositis patients were introduced into cultured myoblasts through electroporation, and their transcriptomic profiles were analysed using RNA sequencing.

RESULTS

In patients with myositis autoantibodies, antibodies accumulated inside myofibres in the same subcellular compartment as the autoantigen. Bulk RNA sequencing revealed that muscle biopsies from patients with autoantibodies targeting transcriptional regulators exhibited transcriptomic patterns consistent with dysfunction of the autoantigen. For instance, in muscle biopsies from patients with anti-PM/Scl autoantibodies recognising components of the nuclear RNA exosome complex, an accumulation of divergent transcripts and long non-coding RNAs was observed; these RNA forms are typically degraded by the nuclear RNA exosome complex. Introducing patient antibodies into cultured muscle cells recapitulated the transcriptomic effects observed in human disease. Further supporting evidence suggested that myositis autoantibodies recognising other autoantigens may also disrupt the function of their targets.

CONCLUSIONS

This study demonstrates that, in myositis, autoantibodies are internalised into living cells, causing biological effects consistent with the disrupted function of their autoantigen.

Distinct Transcript-Level Expression Profiles and Unique Alternative Splicing in Inflammatory Myopathies

OBJECTIVE

The pathogenesis of inflammatory myopathies is poorly understood and there is a need to dissect the transcriptome in more granular ways beyond gene expression.

METHODS

We used a set of muscle RNA-sequencing data from different myositis subtypes grouped by their specific autoantibodies (n = 152). We quantified annotated RNA transcripts for each myositis subtype and identified uniquely expressed RNA as well as transcriptional similarities among myositis types. In addition, we quantified event-based alternative splicing with predicted protein changes. And finally, we searched for cryptic exons.

RESULTS

We saw considerable overlap in RNA expression among subtypes. In addition, MADCAM1 was previously shown to be uniquely expressed in Mi-2 myositis; we discovered it was two noncanonical transcripts that predominantly contributed to the observed increased expression. At the transcriptional level, dermatomyositis subtypes were least similar to inclusion body myositis (IBM) or Jo1, followed by HMGCR, then SRP and other dermatomyositis subtype. Additionally, we discovered many alternative splicing events that were unique by myositis subgroup, including events in muscle dystrophy genes and one event in SRP72, which was seen uniquely in SRP myositis. Finally, we looked for previously reported cryptic exons in IBM and did not find them.

CONCLUSION

The large degree of transcriptional overlap among myositis subtypes reinforces the need to use disease (in addition to healthy) controls to find unique features of autoimmune disease. Unique alterations in the transcriptome that are seen in one myositis subtype and not others advance our understanding of distinct disease pathology.

A comprehensive review of dermatomyositis treatments - from rediscovered classics to promising horizons

INTRODUCTION

Dermatomyositis (DM) is a rare inflammatory disease with diverse cutaneous and systemic manifestations, often associated with myositis-specific antibodies. Managing patients with refractory DM, or individuals presenting pecific complications, like calcinosis or rapidly progressive interstitial lung disease, presents unique challenges.

AREAS COVERED

This review explores current and promising treatment options for DM, drawing from clinical studies, case series, and case reports that consider the underlying disease pathophysiology.

EXPERT OPINION

Recent advancements have improved our understanding and management of DM. The discovery of distinct DM autoantibodies and their correlation with specific clinical phenotypes has transformed patient categorization and enhanced our knowledge of the pathogenesis of the disease. Intravenous immunoglobulin, a well-established treatment in dermatomyositis, has regained prominence and a large randomized clinical trial has reaffirmed its efficacy, confirming it as an effective therapeutic option in this group of patients. Identification of the type I interferon pathway as a key pathogenic mechanism in DM has opened up new avenues for more effective treatment strategies. Blocking the JAK/STAT pathway offers potential for improved management of refractory patients and prevention of highly morbid complications. These recent advancements have significantly impacted the management and care of dermatomyositis patients, enabling tailored approaches, targeted interventions, and improved outcomes for individuals affected by this complex condition.

Idiopathic inflammatory myopathies: current insights and future frontiers

Idiopathic inflammatory myopathies are a group of autoimmune diseases with a broad spectrum of clinical presentations, primarily characterised by immune-mediated muscle injury. Until recently, there was little insight into the pathogenesis of idiopathic inflammatory myopathies, which challenged the recognition of the breadth of heterogeneity of this group of diseases as well as the development of new therapeutics. However, the landscape of idiopathic inflammatory myopathies is evolving. In the past decade, advances in diagnostic tools have facilitated an enhanced understanding of the underlying disease mechanisms in idiopathic inflammatory myopathies, enabling the expansion of therapeutic trials. The fields of transcriptomics, prot§eomics, and machine learning offer the potential to gain greater insights into the underlying pathophysiology of idiopathic inflammatory myopathies. Harnessing insights gained from these sophisticated tools could contribute to the identification of differences at a molecular level among patients, accelerating the development of targeted, tailored therapies. Bolstered by the validation and standardisation of robust outcome measures, many promising therapies are in clinical trial development. Although challenges remain, there is great optimism in the field due to the progress in innovative diagnostics, outcome measures, and therapeutic approaches. In this Review, we discuss the expanding landscape of idiopathic inflammatory myopathies as the frontier of precision medicine becomes imminent.

Pathogenic autoantibody internalization in myositis

Objectives

Myositis is a heterogeneous family of autoimmune muscle diseases. As myositis autoantibodies recognize intracellular proteins, their role in disease pathogenesis has been unclear. This study aimed to determine whether myositis autoantibodies reach their autoantigen targets within muscle cells and disrupt the normal function of these proteins.

Methods

Confocal immunofluorescence microscopy was used to localize antibodies and other proteins of interest in myositis muscle biopsies. Bulk RNA sequencing was used to study the transcriptomic profiles of 668 samples from patients with myositis, disease controls, and healthy controls. Antibodies from myositis patients were introduced into cultured myoblasts by electroporation and the transcriptomic profiles of the treated myoblasts were studied by bulk RNA sequencing.

Results

In patients with myositis autoantibodies, antibodies accumulated inside myofibers in the same subcellular compartment as the autoantigen. Each autoantibody was associated with effects consistent with dysfunction of its autoantigen, such as the derepression of genes normally repressed by Mi2/NuRD in patients with anti-Mi2 autoantibodies, the accumulation of RNAs degraded by the nuclear RNA exosome complex in patients with anti-PM/Scl autoantibodies targeting this complex, and the accumulation of lipids within myofibers of anti-HMGCR-positive patients. Internalization of patient immunoglobulin into cultured myoblasts recapitulated the transcriptomic phenotypes observed in human disease, including the derepression of Mi2/NuRD-regulated genes in anti-Mi2-positive dermatomyositis and the increased expression of genes normally degraded by the nuclear RNA exosome complex in anti-PM/Scl-positive myositis.

Conclusions

In myositis, autoantibodies are internalized into muscle fibers, disrupt the biological function of their autoantigen, and mediate the pathophysiology of the disease.

Shared and Distinctive Transcriptomic and Proteomic Pathways in Adult and Juvenile Dermatomyositis

OBJECTIVE

Transcript and protein expression were interrogated to examine gene locus and pathway regulation in the peripheral blood of active adult dermatomyositis (DM) and juvenile DM patients receiving immunosuppressive therapies.

METHODS

Expression data from 14 DM and 12 juvenile DM patients were compared to matched healthy controls. Regulatory effects at the transcript and protein level were analyzed by multi-enrichment analysis for assessment of affected pathways within DM and juvenile DM.

RESULTS

Expression of 1,124 gene loci were significantly altered at the transcript or protein levels across DM or juvenile DM, with 70 genes shared. A subset of interferon-stimulated genes was elevated, including CXCL10, ISG15, OAS1, CLEC4A, and STAT1. Innate immune markers specific to neutrophil granules and neutrophil extracellular traps were up-regulated in both DM and juvenile DM, including BPI, CTSG, ELANE, LTF, MPO, and MMP8. Pathway analysis revealed up-regulation of PI3K/AKT, ERK, and p38 MAPK signaling, whose central components were broadly up-regulated in DM, while peripheral upstream and downstream components were differentially regulated in both DM and juvenile DM. Up-regulated components shared by DM and juvenile DM included cytokine:receptor pairs LGALS9:HAVCR2, LTF/NAMPT/S100A8/HSPA1A:TLR4, CSF2:CSF2RA, EPO:EPOR, FGF2/FGF8:FGFR, several Bcl-2 components, and numerous glycolytic enzymes. Pathways unique to DM included sirtuin signaling, aryl hydrocarbon receptor signaling, protein ubiquitination, and granzyme B signaling.

CONCLUSION

The combination of proteomics and transcript expression by multi-enrichment analysis broadened the identification of up- and down-regulated pathways among active DM and juvenile DM patients. These pathways, particularly those which feed into PI3K/AKT and MAPK signaling and neutrophil degranulation, may be potential therapeutic targets.

Integrated Multi-Omics Analysis for Inferring Molecular Players in Inclusion Body Myositis

Inclusion body myositis (IBM) is an acquired inflammatory myopathy affecting proximal and distal muscles that leads to weakness in patients over 50. It is diagnosed based on clinical and histological findings in muscle related to inflammation, degeneration, and mitochondria. In relation to IBM, a shortage of validated disease models and a lack of biomarkers and effective treatments constitute an unmet medical need. To overcome these hurdles, we performed an omics analysis of multiple samples from IBM patients (saliva, fibroblasts, urine, plasma, and muscle) to gain insight into the pathophysiology of IBM. Degeneration was evident due to the presence of amyloid β peptide 1-42 (Aβ1-42) in the saliva of the analyzed IBM patients. The presence of metabolic disarrangements in IBM was indicated by an imbalanced organic acid profile in fibroblasts and urine. Specifically, abnormal levels of L-pyroglutamic and orotic acid were supported by the abnormal expression of related metabolites in plasma and urine (glutathione and pyrimidines) and the aberrant expression of upstream gene regulators (L2HGDH, IDH2, OPLAH, and ASL) in muscle. Combined levels of L-pyroglutamic and orotic acid displayed an outstanding biomarker signature in urine with 100% sensitivity and specificity. The confirmation of systemic metabolic disarrangements in IBM and the identification of novel biomarkers reported herein unveil novel insights that require validation in larger cohorts.

Transcriptional derepression of CHD4/NuRD-regulated genes in the muscle of patients with dermatomyositis and anti-Mi2 autoantibodies

OBJECTIVES

Myositis is a heterogeneous family of diseases including dermatomyositis (DM), immune-mediated necrotising myopathy (IMNM), antisynthetase syndrome (AS) and inclusion body myositis (IBM). Myositis-specific autoantibodies define different subtypes of myositis. For example, patients with anti-Mi2 autoantibodies targeting the chromodomain helicase DNA-binding protein 4 (CHD4)/NuRD complex (a transcriptional repressor) have more severe muscle disease than other DM patients. This study aimed to define the transcriptional profile of muscle biopsies from anti-Mi2-positive DM patients.

METHODS

RNA sequencing was performed on muscle biopsies (n=171) from patients with anti-Mi2-positive DM (n=18), DM without anti-Mi2 autoantibodies (n=32), AS (n=18), IMNM (n=54) and IBM (n=16) as well as 33 normal muscle biopsies. Genes specifically upregulated in anti-Mi2-positive DM were identified. Muscle biopsies were stained for human immunoglobulin and protein products corresponding to genes specifically upregulated in anti-Mi2-positive muscle biopsies.

RESULTS

A set of 135 genes, including SCRT1 and MADCAM1, was specifically overexpressed in anti-Mi2-positive DM muscle. This set was enriched for CHD4/NuRD-regulated genes and included genes that are not otherwise expressed in skeletal muscle. The expression levels of these genes correlated with anti-Mi2 autoantibody titres, markers of disease activity and with the other members of the gene set. In anti-Mi2-positive muscle biopsies, immunoglobulin was localised to the myonuclei, MAdCAM-1 protein was present in the cytoplasm of perifascicular fibres, and SCRT1 protein was localised to myofibre nuclei.

CONCLUSIONS

Based on these findings, we hypothesise that anti-Mi2 autoantibodies could exert a pathogenic effect by entering damaged myofibres, inhibiting the CHD4/NuRD complex, and subsequently derepressing the unique set of genes defined in this study.

Transcriptomic profiling reveals distinct subsets of immune checkpoint inhibitor induced myositis

OBJECTIVES

Inflammatory myopathy or myositis is a heterogeneous family of immune-mediated diseases including dermatomyositis (DM), antisynthetase syndrome (AS), immune-mediated necrotising myopathy (IMNM) and inclusion body myositis (IBM). Immune checkpoint inhibitors (ICIs) can also cause myositis (ICI-myositis). This study was designed to define gene expression patterns in muscle biopsies from patients with ICI-myositis.

METHODS

Bulk RNA sequencing was performed on 200 muscle biopsies (35 ICI-myositis, 44 DM, 18 AS, 54 IMNM, 16 IBM and 33 normal muscle biopsies) and single nuclei RNA sequencing was performed on 22 muscle biopsies (seven ICI-myositis, four DM, three AS, six IMNM and two IBM).

RESULTS

Unsupervised clustering defined three distinct transcriptomic subsets of ICI-myositis: ICI-DM, ICI-MYO1 and ICI-MYO2. ICI-DM included patients with DM and anti-TIF1γ autoantibodies who, like DM patients, overexpressed type 1 interferon-inducible genes. ICI-MYO1 patients had highly inflammatory muscle biopsies and included all patients that developed coexisting myocarditis. ICI-MYO2 was composed of patients with predominant necrotising pathology and low levels of muscle inflammation. The type 2 interferon pathway was activated both in ICI-DM and ICI-MYO1. Unlike the other types of myositis, all three subsets of ICI-myositis patients overexpressed genes involved in the IL6 pathway.

CONCLUSIONS

We identified three distinct types of ICI-myositis based on transcriptomic analyses. The IL6 pathway was overexpressed in all groups, the type I interferon pathway activation was specific for ICI-DM, the type 2 IFN pathway was overexpressed in both ICI-DM and ICI-MYO1 and only ICI-MYO1 patients developed myocarditis.

Molecular signature of neutrophil extracellular trap mediating disease module in idiopathic inflammatory myopathy

The rarity and heterogeneity of idiopathic inflammatory myopathy (IIM) pose challenges for researching IIM in affected individuals. We analyzed integrated transcriptomic datasets obtained using muscle tissues from patients with five distinct IIM subtypes to investigate the shared and distinctive cellular and molecular characteristics. A transcriptomic dataset of muscle tissues from normal controls (n = 105) and patients with dermatomyositis (n = 89), polymyositis (n = 33), inclusion body myositis (n = 121), immune-mediated necrotizing myositis (n = 75), and anti-synthetase syndrome (n = 18) was used for differential gene-expression analysis, functional-enrichment analysis, gene set-enrichment analysis, disease-module identification, and kernel-based diffusion scoring. Damage-associated molecular pattern-associated pathways and neutrophil-mediated immunity were significantly enriched across different IIM subtypes, although their activities varied. Interferons-signaling pathways were differentially activated across all five IIM subtypes. In particular, neutrophil extracellular trap (NET) formation was significantly activated and correlated with Fcγ R-mediated signaling pathways. NET formation-associated genes were key for establishing disease modules, and FCGRs, C1QA, and SERPINE1 markedly perturbed the disease modules. Integrated transcriptomic analysis of muscle tissues identified NETs as key components of neutrophil-mediated immunity involved in the pathogenesis of IIM subtypes and, thus, has therapeutically targetable value.

Inclusion body myositis: evolving concepts

PURPOSE OF REVIEW

To discuss recent developments in our understanding of epidemiology, diagnostics, biomarkers, pathology, pathogenesis, outcome measures, and therapeutics in inclusion body myositis (IBM).

RECENT FINDINGS

Recent epidemiology data confirms a relatively higher prevalence in the population aged above 50 years and the reduced life expectancy. Association with cancer and other systemic disorders is better defined. The role of magnetic resonance imaging (MRI) and ultrasound in diagnosis as well as in following disease progression has been elucidated. There are new blood and imaging biomarkers that show tremendous promise for diagnosis and as outcome measures in therapeutic trials. Improved understanding of the pathogenesis of the disease will lead to better therapeutic interventions, but also highlights the importance to have sensitive and responsive outcome measures that accurately quantitate change.

SUMMARY

There are exciting new developments in our understanding of IBM which should lead to improved management and therapeutic options.

The Genetics of Autoimmune Myositis

The idiopathic inflammatory myopathies (IIM) are rare, heterogeneous systemic autoimmune disorders, characterized by inflammation of skeletal muscle and multi-organ involvement. Studies to identify genetic risk factors and dysregulated gene expression in IIM aim to increase our understanding of disease pathogenesis. Genome-wide association studies have confirmed the HLA region as the most strongly associated region in IIM, with different associations between clinically-defined subgroups. Associated genes are involved in both the innate and adaptive immune response, while identification of variants reported in other autoimmune disorders suggests shared biological pathways. Targeted imputation analysis has identified key associated amino acid residues within HLA molecules that may influence antigen recognition. These amino acids increase risk for specific clinical phenotypes and autoantibody subgroups, and suggest that serology-defined subgroups may be more homogeneous. Recent data support the contribution of rare genetic variation to disease susceptibility in IIM, including mitochondrial DNA variation in sporadic inclusion body myositis and somatic mutations and loss of heterozygosity in cancer-associated myositis. Gene expression studies in skeletal muscle, blood and skin from individuals with IIM has confirmed the role of interferon signalling and other dysregulated pathways, and identified cell-type specific signatures. These dysregulated genes differentiate IIM subgroups and identify potential biomarkers. Here, we review recent genetic studies in IIM, and how these inform our understanding of disease pathogenesis and provide mechanistic insights into biological pathways.

Pathophysiological Mechanisms and Treatment of Dermatomyositis and Immune Mediated Necrotizing Myopathies: A Focused Review

Idiopathic inflammatory myopathies (IIM), collectively known as myositis, are a composite group of rare autoimmune diseases affecting mostly skeletal muscle, although other organs or tissues may also be involved. The main clinical feature of myositis is subacute, progressive, symmetrical muscle weakness in the proximal arms and legs, whereas subtypes of myositis may also present with extramuscular features, such as skin involvement, arthritis or interstitial lung disease (ILD). Established subgroups of IIM include dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASyS), overlap myositis (OM) and inclusion body myositis (IBM). Although these subgroups have overlapping clinical features, the widespread variation in the clinical manifestations of IIM suggests different pathophysiological mechanisms. Various components of the immune system are known to be important immunopathogenic pathways in IIM, although the exact pathophysiological mechanisms causing the muscle damage remain unknown. Current treatment, which consists of glucocorticoids and other immunosuppressive or immunomodulating agents, often fails to achieve a sustained beneficial response and is associated with various adverse effects. New therapeutic targets have been identified that may improve outcomes in patients with IIM. A better understanding of the overlapping and diverging pathophysiological mechanisms of the major subgroups of myositis is needed to optimize treatment. The aim of this review is to report on recent advancements regarding DM and IMNM.

Neuromuscular disease: 2022 update

This review highlights ten important advances in the neuromuscular disease field that were reported in 2021. As with prior updates in this article series, the overarching topics include (i) advances in understanding of fundamental neuromuscular biology; (ii) new / emerging diseases; (iii) advances in understanding of disease etiology and pathogenesis; (iii) diagnostic advances; and (iv) therapeutic advances. Within this general framework, the individual disease entities that are discussed in more detail include neuromuscular complications of COVID-19 (another look at the topic first covered in the 2021 review), autosomal recessive myopathy caused by MLIP mutations, autosomal recessive neuromuscular disease caused by VWA1 mutations, Leber's hereditary optic neuropathy, myopathies with autophagic defects, tRNA synthetase-associated Charcot-Marie-Tooth disease, systemic sclerosis-associated myopathy, humoral immune endoneurial microvasculopathy, and late-onset Pompe disease. In addition, the review highlights a few other advances (including new insights into mechanisms of muscle and nerve regeneration and the use of gene expression profiling to better characterize different subtypes of immune-mediated myopathies) that will be of significant interest for clinicians and researchers who specialize in neuromuscular disease.