Development and evaluation of a standardized ELISA for the determination of autoantibodies against cN-1A (Mup44, NT5C1A) in sporadic inclusion body myositis

Association of HLA-DR, HLA-DQ, and HLA-B alleles with inclusion body myositis risk: A systematic review, a meta-analysis, a meta-regression and a trial sequential analysis

INTRODUCTION

Although, several studies have assessed the association of HLA Class I and II genes with inclusion body myositis (IBM), results were inconsistent and between-studies heterogeneity needs to be investigated.

OBJECTIVES

The aim of this review was to summarize existing data on the contribution of HLA-DRB1 and HLA-B alleles to IBM susceptibility and to investigate the between-studies heterogeneity by subgroup analyses and meta-regressions.

DESIGN

This study was performed according to the PRISMA guidelines for systematic reviews and meta-analyses.

METHODS

An electronic literature search for eligible studies among all papers published prior to January 29, 2025, was conducted through PubMed, EMBASE, Web of science, and Scopus databases. Meta-analyses together with subgroup analyses and meta-regressions were performed for the two following HLA genes: HLA-DRB1 and HLA-B.

RESULTS

Combined analyses revealed a significant increase in IBM risk conferred by the HLA-DRB1*03 allele (9.21 (7.05-12.01)), the DRB*03:01 allele (8.44 (6.85-10.41)), the DRB1*01 allele (2.31 (1.82-2.93)), the DRB1*01:01 allele (2.63 (1.95-3.55)), the DRB1*15:02 allele (3.49 (2.12-5.75)), the B*08 allele (4.05 (2.58-6.38)), and the DQB1*02 allele (6.62 (4.5-9.74)), all p-values < 0.001. In addition, the DRB1*15:01 allele was found to be protective against IBM in all populations (0.48 (0.32-0.72)). Conversely, the DRB*11 allele was not associated with IBM risk, OR (95% CI) = 0.91 (0.54-1.51), p = 0.703.

CONCLUSION

This meta-analysis demonstrated that HLA-DRB1, DQB1, and B loci could play a major role in IBM pathogenesis.

REGISTRATION

This review has been registered on PROSPERO on June 25, 2024: CRD42024557948, Available from: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42024557948.

Anti-Cytosolic 5'-Nucleotidase 1A in the Diagnosis of Patients with Suspected Idiopathic Inflammatory Myopathies: An Italian Real-Life, Single-Centre Retrospective Study

BACKGROUND

Anti-cytosolic 5'-nucleotidase 1A (anti-cN1A) antibodies were proposed as a biomarker for the diagnosis of inclusion body myositis (IBM), but conflicting specificity and sensitivity evidence limits its use. Our study aimed to assess the diagnostic accuracy of anti-cN1A in a cohort of patients who underwent a myositis line immunoassay for suspected idiopathic inflammatory myopathies (IIM). We also assessed the agreement between two testing procedures: line immunoassay (LIA) and enzyme-linked immunoassay (ELISA).

MATERIALS AND METHODS

We collected retrospective clinical and serological data for 340 patients who underwent a myositis antibody assay using LIA (EUROLINE Autoimmune Inflammatory Myopathies 16 Ag et cN-1A (IgG) line immunoassay) and verification with an anti-cN1A antibody assay using ELISA (IgG) (Euroimmun Lubeck, Germany).

RESULTS

The serum samples of 20 (5.88%) patients (15 females, 5 males, mean age 58.76 ± 18.31) tested positive for anti-cN1A using LIA, but only two out of twenty were diagnosed with IBM. Seventeen out of twenty tested positive for anti-cN1A using ELISA (median IQR, 2.9 (1.9-4.18)).

CONCLUSIONS

Our study suggests excellent concordance between LIA and ELISA for detecting anti-cN1A antibodies. LIA may be a rapid and useful adjunct, and it could even replace ELISA for cN1A assay. However, the high prevalence of diseases other than IBM in our cohort of anti-cN1A-positive patients did not allow us to consider anti-cN1A antibodies as a specific biomarker for IBM.

Myositis-related autoantibody profile and clinical characteristics stratified by anti-cytosolic 5'-nucleotidase 1A status in connective tissue diseases

INTRODUCTION/AIMS

Cytosolic 5'-nucleotidase 1A (cN-1A) autoantibodies have been recognized as myositis-related autoantibodies. However, their correlations with clinical characteristics and other myositis-specific and myositis-associated autoantibodies (MSAs/MAAs) are still unclear. We aimed to establish the prevalence and clinical and laboratory associations of cN-1A autoantibodies in a cohort of patients with connective tissue diseases.

METHODS

A total of 567 participants (182 idiopathic inflammatory myopathies [IIM], 164 systemic lupus erythematosus [SLE], 121 systemic sclerosis [SSc], and 100 blood donors [BD]) were tested for the presence of cN-1A autoantibodies and other myositis-specific and myositis-associated autoantibodies (MSAs/MAAs). Clinical and laboratory characteristics were compared between anti-cN-1A positive and negative patients with sporadic inclusion body myositis (sIBM) and between anti-cN-1A positive and negative patients with non-IBM IIM.

RESULTS

In the sIBM cohort, 30 patients (46.9%) were anti-cN-1A positive vs. 18 (15.2%) in the non-IBM IIM cohort, 17 (10%) were anti-cN-1A positive in the SLE cohort and none in the SSc or the BD cohorts. Anti-cN-1A positivity had an overall sensitivity of 46.9% and a specificity of 93.2% for sIBM. Dysphagia was more frequent in the anti-cN-1A positive vs. negative sIBM patients (p = .04). In the non-IBM IIM group, being anti-cN-1A antibody positive was associated with the diagnosis polymyositis (p = .04) and overlap-myositis (p = .04) and less disease damage evaluated by physician global damage score (p < .001).

DISCUSSION

cN-1A autoantibodies were predominantly found in IIM patients and was associated with dysphagia in sIBM patients. Notably, anti-cN-1A appears to identify a distinct phenotype of anti-cN-1A positive non-IBM IIM patients with a milder disease course.

Idiopathic inflammatory myopathies: a review

Idiopathic inflammatory myopathy (IIM) is the umbrella term including dermatomyositis (DM), polymyositis (PM), overlap myositis (OM), sporadic inclusion body myositis (IBM) and necrotising autoimmune myopathy (NAM), also known as immune-mediated necrotising myopathy. There is some debate as to whether PM exists as a discrete entity, or perhaps is an overly generalising term encompassing connective tissue disease associated myositis, or OM, and the previously poorly recognised NAM. As such, PM will not be covered in detail in this review. DM, OM and NAM all present similarly, with proximal weakness and elevated creatine kinase (CK) level. By contrast, IBM preferentially involves the long finger flexors and quadriceps, and presents with a normal or only mildly elevated CK. Developments in serological testing and imaging are shifting the diagnostic paradigm away from a reliance on histopathology. The therapeutic armamentarium for IIM continues to evolve, with intravenous immunoglobulin and rituximab proving to be successful for refractory disease. This review will provide a diagnostic algorithm for the clinician to help distinguish between IIM subtypes - with emphasis on clinical assessment, serology and imaging, as well as discussion of therapeutic options and escalation of immunotherapy.

Significance of Sjögren's syndrome and anti-cN1A antibody in myositis patients

OBJECTIVE

We recently recorded a high prevalence of inclusion body myositis (IBM) in patients with Sjögren's syndrome (SS). Whether myositis patients with SS differ from myositis patients without SS in terms of the characteristics of the myositis is currently unknown. Anti-cytosolic 5'-nucleotidase 1 A (cN1A) has recently been proposed as a biomarker for IBM but is also frequent in SS. Whether anti-cN1A is independently associated with IBM is still an open question. We aimed to assess the significance of SS and anti-cN1A in myositis patients.

METHODS

Cumulative data on all myositis patients (EULAR/ACR 2017 criteria) screened for SS (ACR/EULAR 2016 criteria) in a single center were analyzed. Ninety-nine patients were included, covering the whole spectrum of EULAR/ACR 2017 myositis subgroups and with a median follow-up of 6 years [range 1.0-37.5]. The 34 myositis patients with SS (myositis/SS+) were compared with the 65 myositis patients without SS (myositis/SS-).

RESULTS

IBM was present in 24% of the myositis/SS+ patients vs 6% of the myositis/SS- group (p = 0.020). None of the IBM patients responded to treatment, whether they had SS or not. Anti-cN1A was more frequent in myositis/SS+ patients (38% vs 6%, p = 0.0005), independently of the higher prevalence of IBM in this group (multivariate p-value: 0.02). Anti-cN1A antibody specificity for IBM was 0.96 [95% CI, 0.87-0.99] in the myositis SS- group but dropped to 0.70 [95% CI, 0.48-0.85] in the myositis SS/+ group.

INTERPRETATION

In myositis patients, SS is associated with IBM and with anti-cN1A antibodies, independently of the IBM diagnosis. As a consequence, anti-cN1A has limited specificity for IBM in myositis patients with SS.

Anti-cN1A Antibodies Are Associated with More Severe Dysphagia in Sporadic Inclusion Body Myositis

In recent years, an autoantibody directed against the 5'-citosolic nucleotidase1A (cN1A) was identified in the sera of sporadic inclusion body myositis (s-IBM) patients with widely variable sensitivity (33%-76%) and specificity (87%-100%). We assessed the sensitivity/specificity of anti-cN1A antibodies in an Italian cohort of s-IBM patients, searching for a potential correlation with clinical data. We collected clinical data and sera from 62 consecutive s-IBM patients and 62 other inflammatory myopathies patients. Testing for anti-cN1A antibodies was performed using a commercial ELISA. Anti-cN1A antibodies were detected in 23 s-IBM patients, resulting in a sensitivity of 37.1% with a specificity of 96.8%. Positive and negative predictive values were 92.0% and 60.6%, respectively. We did not find significant difference regarding demographic variables, nor quadriceps or finger flexor weakness. Nevertheless, we found that anti-cN1A-positive patients presented significantly lower scores in IBMFRS item 1 (swallowing, p = 0.045) and more frequently reported more severe swallowing problems, expressed as an IBMFRS item 1 score ≤ 2 (p < 0.001). We confirmed the low sensitivity and high specificity of anti-cN1A Ab in s-IBM patients with a high positive predictive value. The presence of anti-CN1A antibodies identified patients with a greater risk of more severe dysphagia.

Clinical utility of anti-cytosolic 5'-nucleotidase 1A antibody in idiopathic inflammatory myopathies

Objective

To define the clinicopathologic features and diagnostic utility associated with anti‐cytosolic 5′‐nucleotidase 1A (NT5C1A) antibody seropositivity in idiopathic inflammatory myopathies (IIMs).

Methods

Anti‐NT5C1A antibody status was clinically tested between 2014 and 2019 in the Washington University neuromuscular clinical laboratory. Using clinicopathologic information available for 593 patients, we classified them as inclusion body myositis (IBM), dermatomyositis, antisynthetase syndrome, immune‐mediated necrotizing myopathy (IMNM), nonspecific myositis, or noninflammatory muscle diseases.

Results

Of 593 patients, anti‐NT5C1A antibody was found in 159/249 (64%) IBM, 11/53 (21%) dermatomyositis, 7/27 (26%) antisynthetase syndrome, 9/76 (12%) IMNM, 20/84 (24%) nonspecific myositis, and 6/104 (6%) noninflammatory muscle diseases patients. Among patients with IBM, anti‐NT5C1A antibody seropositive patients had more cytochrome oxidase‐negative fibers compared with anti‐NT5C1A antibody seronegative patients. Among 14 IBM patients initially negative for anti‐NT5C1A antibody, three patients (21%) converted to positive. Anti‐NT5C1A antibody seropositivity did not correlate with malignancy, interstitial lung disease, response to treatments in dermatomyositis, antisynthetase syndrome, and IMNM, or survival in IIMs.

Interpretation

Anti‐NT5C1A antibody is associated with IBM. However, the seropositivity can also be seen in non‐IBM IIMs and it does not correlate with any prognostic factors or survival.

Anti-Cytosolic 5'-Nucleotidase 1A Autoantibodies Are Absent in Juvenile Dermatomyositis

Objective

To assess anti–cytosolic 5′‐nucleotidase 1A (anti–cN‐1A) autoantibodies in children with juvenile dermatomyositis (DM) and healthy controls, using 3 different methods of antibody detection, as well as verification of the results in an independent cohort.

Methods

Anti–cN‐1A reactivity was assessed in 34 Dutch juvenile DM patients and 20 healthy juvenile controls using the following methods: a commercially available full‐length cN‐1A enzyme‐linked immunosorbent assay (ELISA), a synthetic peptide ELISA, and immunoblotting with a lysate from cN‐1A–expressing HEK 293 cells. Sera from juvenile DM patients with active disease and those with disease in remission were analyzed. An independent British cohort of 110 juvenile DM patients and 43 healthy juvenile controls was assessed using an in‐house full‐length cN‐1A ELISA.

Results

Anti–cN‐1A reactivity was not present in sera from juvenile DM patients or healthy controls when tested with the commercially available full‐length cN‐1A ELISA or by immunoblotting, in either active disease or disease in remission. Additionally, in the British juvenile DM cohort, anti–cN‐1A reactivity was not detected. Three Dutch juvenile DM patients had weakly positive results for 1 of 3 synthetic cN‐1A peptides measured by ELISA.

Conclusion

Juvenile DM patients and young healthy individuals did not show anti–cN‐1A reactivity as assessed by different antibody detection techniques.

Anti-cN1A antibodies do not correlate with specific clinical, electromyographic, or pathological findings in sporadic inclusion body myositis

BACKGROUND

Anti-cytosolic 5'-nucleotidase 1A (cN1A) antibodies are commonly detected in patients with sporadic inclusion body myositis (sIBM). However, their pathogenic role has not been established. Moreover, efforts toward identifying sIBM distinct clinicopathologic characteristics associated with these antibodies have yielded conflicting results.

METHODS

We first searched for patients, seen in our clinics, tested for anti-cN1A antibodies between December 2015 and December 2019. We identified 92 patients who were diagnosed with sIBM, according to the 2011 ENMC or Griggs et al criteria. Thereafter, we reviewed and compared the clinical and investigational findings of these patients in relation to their antibody status.

RESULTS

Anti-cN1A antibodies were present in 47/92 (51%) patients with sIBM. Comparison of seropositive and seronegative cohorts yielded no significant difference in clinical features, including facial weakness, oropharyngeal and respiratory involvement, or disease severity. The antibody titer did not correlate with the clinical phenotype, CK value, or presence of myotonic discharges on EMG. Anti-cN1A antibody positive patients appeared to have more frequent auto-aggressive inflammation on muscle biopsy but not as an isolated myopathological feature.

CONCLUSIONS

Our study showed that anti-cN1A antibody positive and negative sIBM patients have similar clinical features and disease severity. Anti-cN1A antibodies in our sIBM cohort did not correlate with any studied clinical or laboratory parameter and, therefore, were of limited value in the patient's assessment.

Prevalence of Novel Myositis Autoantibodies in a Large Cohort of Patients with Interstitial Lung Disease

Connective tissue diseases (CTDs) are an important secondary cause of interstitial lung disease (ILD). If a CTD is suspected, clinicians are recommended to perform autoantibody testing, including for myositis autoantibodies. In this study, the prevalence and clinical associations of novel myositis autoantibodies in ILD are presented. A total of 1194 patients with ILD and 116 healthy subjects were tested for antibodies specific for Ks, Ha, Zoα, and cN1A with a line-blot assay on serum available at the time of diagnosis. Autoantibodies were demonstrated in 63 (5.3%) patients and one (0.9%) healthy control (p = 0.035). Autoantibodies were found more frequently in females (p = 0.042) and patients without a histological and/or radiological usual interstitial pneumonia (UIP; p = 0.010) and a trend towards CTD-ILDs (8.4%) was seen compared with other ILDs (4.9%; p = 0.090). The prevalence of antibodies specific for Ks, Ha, Zoα, and cN1A was, respectively, 1.3%, 2.0%, 1.4%, and 0.9% in ILD. Anti-Ha and Anti-Ks were observed in males with unclassifiable idiopathic interstitial pneumonia (unclassifiable IIP), hypersensitivity pneumonitis (HP), and various CTD-ILDs, whereas anti-cN1A was seen in females with antisynthetase syndrome (ASS), HP, and idiopathic pulmonary fibrosis (IPF). Anti-Zoα was associated with CTD-ILD (OR 2.5; 95%CI 1.11-5.61; p = 0.027). In conclusion, a relatively high prevalence of previously unknown myositis autoantibodies was found in a large cohort of various ILDs. Our results contribute to the awareness that circulating autoantibodies can be found in ILDs with or without established CTD. Whether these antibodies have to be added to the standard set of autoantibodies analysed in conventional myositis blot assays for diagnostic purposes in clinical ILD care requires further study.

Inclusion body myositis in patients with spinocerebellar ataxia types 3 and 6

OBJECTIVES

To describe the combination of spinocerebellar ataxia (SCA) types 3 and 6 and sporadic inclusion body myositis (IBM).

METHODS

A description of five patients with SCA type 3 and 6 who were diagnosed with IBM. We explore possible mechanisms explaining the coexistence of both diseases.

RESULTS

The patients with SCA-3 (n=4) and SCA-6 (n=1) developed asymmetric muscle weakness in a pattern suggestive of IBM in the course of their disease. Based on findings of neurological examination and additional investigations (muscle ultrasound, muscle biopsy), the diagnosis of IBM was made in all patients.

CONCLUSION

We report on five patients with concomitant SCA and IBM. Our cases may merely illustrate coincidental co-occurrence of IBM and SCA-3/SCA-6. However, the presence of SCA mutations could predispose to the development of IBM in some SCA patients, or, the presence of toxic aggregates and malfunctioning of cellular quality control processes in both diseases could indicate a convergence of disease mechanisms.

Inclusion body myositis: clinical features and pathogenesis

Inclusion body myositis (IBM) is often viewed as an enigmatic disease with uncertain pathogenic mechanisms and confusion around diagnosis, classification and prospects for treatment. Its clinical features (finger flexor and quadriceps weakness) and pathological features (invasion of myofibres by cytotoxic T cells) are unique among muscle diseases. Although IBM T cell autoimmunity has long been recognized, enormous attention has been focused for decades on several biomarkers of myofibre protein aggregates, which are present in <1% of myofibres in patients with IBM. This focus has given rise, together with the relative treatment refractoriness of IBM, to a competing view that IBM is not an autoimmune disease. Findings from the past decade that implicate autoimmunity in IBM include the identification of a circulating autoantibody (anti-cN1A); the absence of any statistically significant genetic risk factor other than the common autoimmune disease 8.1 MHC haplotype in whole-genome sequencing studies; the presence of a marked cytotoxic T cell signature in gene expression studies; and the identification in muscle and blood of large populations of clonal highly differentiated cytotoxic CD8⁺ T cells that are resistant to many immunotherapies. Mounting evidence that IBM is an autoimmune T cell-mediated disease provides hope that future therapies directed towards depleting these cells could be effective.

Association Between Treatment-Resistant Sarcoid Myopathy and Inclusion Body Myositis

The association between sarcoid myopathy and inclusion body myositis is a rare phenomenon that is not well understood. In this case, we present a 46-year-old female with a five-year history of sarcoidosis who became refractory to treatment, experiencing progressive deterioration and muscle wasting. The patient’s distribution of muscle weakness did not follow characteristic patterns of inclusion body myositis. Yet, a subsequent deltoid biopsy revealed diagnostic findings typical of inclusion body myositis. This case report reveals an association between treatment-resistant sarcoid myopathy and the evolution of inclusion body myositis in the absence of characteristic clinical findings.

Autoantibodies in Myositis. How to Achieve a Comprehensive Strategy for Serological Testing

Myopathies are a rare type of acquired, chronic autoimmune diseases of the skeletal muscles and affect both children and adults. The hallmark symptoms of idiopathic inflammatory myopathies (IIM) are muscle inflammation, proximal muscle weakness and disability, arthritis, cutaneous rashes, calcinosis, ulceration, malignancy and interstitial lung disease (ILD). Subforms of IIM include polymyositis, dermatomyositis, cancer-related myositis and sporadic inclusion body myositis. Autoantibodies function as biomarkers for diagnosis of IIM and can be used to delimit clinically distinguishable IIM subforms. To maximise the diagnostic information it is essential to perform comprehensive multiparametric serological testing including both screening and confirmation tests.

Idiopathic inflammatory myopathies overlapping with systemic diseases

A muscle biopsy is currently requested to assess the diagnosis of an idiopathic inflammatory myopathy overlapping with a systemic disease. During the past few years, the classification of inflammatory myopathy subtypes has been revisited progressively on the basis of correlations between clinical phenotypes, autoantibodies and histological data. Several syndromic entities are now more clearly defined, and the aim of the present review is to clarify the contribution of muscle biopsy in a setting of idiopathic inflammatory myopathies overlapping with systemic diseases.
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Sensitivity and clinical utility of the anti-cytosolic 5'-nucleotidase 1A (cN1A) antibody test in sporadic inclusion body myositis: Report of 40 patients from a single neuromuscular center

Sporadic inclusion body myositis (IBM) is the most common acquired myopathy affecting patients over age 50. The discovery of an autoantibody directed against a 43-44 kD protein (anti-cytosolic-5'-nucleotidase 1A or anti-cN1A) has provided support for the hypothesis of an immune-mediated pathogenesis. Previous studies have reported variable test sensitivity and specificity, and inconsistent results on the predictive value. In our cohort of 40 patients with clinico-pathologically or clinically defined IBM, we found the sensitivity of the anti-cN1A antibody test to be 50%. Comparing characteristics for test positive and test negative groups, we found that patients in our cohort testing positive for the anti-cN1A antibody were significantly more likely to be older than age 60 years at symptom onset. We found no positive association between anti-cN1A reactivity and other clinical, laboratory, and muscle histopathologic findings. Based on all clinical studies published to date including the present, the anti-cN1A antibody test shows high diagnostic specificity, moderate sensitivity, and a low predictive value in regards to age of onset, disease severity and other associated clinicopathological findings.

Autoantibodies to Cytosolic 5'-Nucleotidase 1A in Primary Sjögren's Syndrome and Systemic Lupus Erythematosus

Introduction

Autoantibodies to cytosolic 5′-nucleotidase 1A (cN-1A; NT5C1A) have a high specificity when differentiating sporadic inclusion body myositis from polymyositis and dermatomyositis. In primary Sjögren’s syndrome (pSS) and systemic lupus erythematosus (SLE) anti-cN-1A autoantibodies can be detected as well. However, various frequencies of anti-cN-1A reactivity have been reported in SLE and pSS, which may at least in part be explained by the different assays used. Here, we determined the occurrence of anti-cN-1A reactivity in a large number of patients with pSS and SLE using one standardized ELISA.

Methods

Sera from pSS (n = 193) and SLE patients (n = 252) were collected in five European centers. Anti-cN-1A, anti-Ro52, anti-nucleosome, and anti-dsDNA reactivities were tested by ELISA (Euroimmun AG) in a single laboratory. Correlations of anti-cN-1A reactivity with demographic data and clinical data (duration of disease at the moment of serum sampling, autoimmune comorbidity and presence of muscular symptoms) were analyzed using SPSS software.

Results

Anti-cN-1A autoantibodies were found on average in 12% of pSS patients, with varying frequencies among the different cohorts (range: 7–19%). In SLE patients, the anti-cN-1A positivity on average was 10% (range: 6–21%). No relationship was found between anti-cN-1A reactivity and the presence or absence of anti-Ro52, anti-nucleosome, and anti-dsDNA reactivity in both pSS and SLE. No relationship between anti-cN-1A reactivity and duration of disease at the moment of serum sampling and the duration of serum storage was observed. The frequency of muscular symptoms or viral infections did not differ between anti-cN-1A-positive and -negative patients. In both disease groups anti-cN-1A-positive patients suffered more often from other autoimmune diseases than the anti-cN-1A-negative patients (15 versus 5% (p = 0.05) in pSS and 50 versus 30% (p = 0.02) in SLE).

Conclusion

Our results confirm the relatively frequent occurrence of anti-cN-1A in pSS and SLE patients and the variation in anti-cN-1A reactivity between independent groups of these patients. The explanation for this variation remains elusive. The correlation between anti-cN-1A reactivity and polyautoimmunity should be evaluated in future studies. We conclude that anti-cN-1A should be classified as a myositis-associated-, not as a myositis-specific-autoantibody based on its frequent presence in SLE and pSS.

Anti-NT5C1A autoantibodies are associated with more severe disease in patients with juvenile myositis

OBJECTIVES

Autoantibodies recognising cytosolic 5'-nucleotidase 1A (NT5C1A) are found in adult patients with myositis and other autoimmune diseases. They are especially prevalent in adults with inclusion body myositis (IBM), in which they are associated with more severe weakness and higher mortality. This study was undertaken to define the prevalence and clinical features associated with anti-NT5C1A autoantibodies in juvenile myositis.

METHODS

We screened sera from 380 patients with juvenile myositis, 30 patients with juvenile idiopathic arthritis (JIA) and 92 healthy control children for anti-NT5C1A autoantibodies. Clinical characteristics were compared between patients with myositis with and without anti-NT5C1A autoantibodies.

RESULTS

Anti-NT5C1A autoantibodies were present in 102 of 380 (27%) patients with juvenile myositis and in 11 of 92 (12%) healthy control children (P=0.002) and 27% of children with JIA (P=0.05 vs controls). Sera of 83 of 307 (27%) patients with juvenile dermatomyositis and 16 of 46 (35%) patients with juvenile overlap myositis were anti-NT5C1A autoantibody-positive (P<0.01 vs healthy controls for each), but sera of only 3 of 27 (11%) patients with juvenile polymyositis were anti-NT5C1A-positive. Patients with juvenile myositis with and without anti-NT5C1A autoantibodies had similar clinical phenotypes. However, patients with anti-NT5C1A autoantibody-positive myositis had greater pulmonary symptoms at diagnosis (P=0.005), more frequent hospitalisations (P=0.01) and required a larger number of medications (P<0.001).

CONCLUSION

Anti-NT5C1A autoantibodies are present in more than one-quarter of children with juvenile myositis and JIA compared with only 12% of healthy children, suggesting they are myositis-associated in children. As in adults with IBM, patients with juvenile myositis with anti-NT5C1A autoantibodies have more severe disease.

Bench to bedside review of myositis autoantibodies

Idiopathic inflammatory myopathies represent a heterogeneous group of autoimmune diseases with systemic involvement. Even though numerous specific autoantibodies have been recognized, they have not been included, with the only exception of anti-Jo-1, into the 2017 Classification Criteria, thus perpetuating a clinical-serologic gap. The lack of homogeneous grouping based on the antibody profile deeply impacts the diagnostic approach, therapeutic choices and prognostic stratification of these patients. This review is intended to highlight the comprehensive scenario regarding myositis-related autoantibodies, from the molecular characterization and biological significance to target antigens, from the detection tools, with a special focus on immunofluorescence patterns on HEp-2 cells, to their relative prevalence and ethnic diversity, from the clinical presentation to prognosis. If, on the one hand, a notable body of literature is present, on the other data are fragmented, retrospectively based and collected from small case series, so that they do not sufficiently support the decision-making process (i.e. therapeutic approach) into the clinics.