HLA-DRB1 allele and autoantibody profiles in Japanese patients with inclusion body myositis

Sporadic Inclusion Body Myositis at the Crossroads between Muscle Degeneration, Inflammation, and Aging

Sporadic inclusion body myositis (sIBM) is the most common muscle disease of older people and is clinically characterized by slowly progressive asymmetrical muscle weakness, predominantly affecting the quadriceps, deep finger flexors, and foot extensors. At present, there are no enduring treatments for this relentless disease that eventually leads to severe disability and wheelchair dependency. Although sIBM is considered a rare muscle disorder, its prevalence is certainly higher as the disease is often undiagnosed or misdiagnosed. The histopathological phenotype of sIBM muscle biopsy includes muscle fiber degeneration and endomysial lymphocytic infiltrates that mainly consist of cytotoxic CD8+ T cells surrounding nonnecrotic muscle fibers expressing MHCI. Muscle fiber degeneration is characterized by vacuolization and the accumulation of congophilic misfolded multi-protein aggregates, mainly in their non-vacuolated cytoplasm. Many players have been identified in sIBM pathogenesis, including environmental factors, autoimmunity, abnormalities of protein transcription and processing, the accumulation of several toxic proteins, the impairment of autophagy and the ubiquitin-proteasome system, oxidative and nitrative stress, endoplasmic reticulum stress, myonuclear degeneration, and mitochondrial dysfunction. Aging has also been proposed as a contributor to the disease. However, the interplay between these processes and the primary event that leads to the coexistence of autoimmune and degenerative changes is still under debate. Here, we outline our current understanding of disease pathogenesis, focusing on degenerative mechanisms, and discuss the possible involvement of aging.

HLA Genetics for the Human Diseases

Highly polymorphic human leukocyte antigen (HLA) molecules (alleles) expressed by different classical HLA class I and class II genes have crucial roles in the regulation of innate and adaptive immune responses, transplant rejection and in the pathogenesis of numerous infectious and autoimmune diseases. To date, over 35,000 HLA alleles have been published from the IPD-IMGT/HLA database, and specific HLA alleles and HLA haplotypes have been reported to be associated with more than 100 different diseases and phenotypes. Next generation sequencing (NGS) technology developed in recent years has provided breakthroughs in various HLA genomic/gene studies and transplant medicine. In this chapter, we review the current information on the HLA genomic structure and polymorphisms, as well as the genetic context in which numerous disease associations have been identified in this region.

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.

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.