Robert G. Cooper

Disease specificity of autoantibodies to cytosolic 5'-nucleotidase 1A in sporadic inclusion body myositis versus known autoimmune diseases

Objectives The diagnosis of inclusion body myositis (IBM) can be challenging as it can be difficult to clinically distinguish from other forms of myositis, particularly polymyositis (PM). Recent studies have shown frequent presence of autoantibodies directed against cytosolic 5′-nucleotidase 1A (cN-1A) in patients with IBM. We therefore, examined the autoantigenicity and disease specificity of major epitopes of cN-1A in patients with sporadic IBM compared with healthy and disease controls. Methods Serum samples obtained from patients with IBM (n=238), PM and dermatomyositis (DM) (n=185), other autoimmune diseases (n=246), other neuromuscular diseases (n=93) and healthy controls (n=35) were analysed for the presence of autoantibodies using immunodominant cN-1A peptide ELISAs. Results Autoantibodies directed against major epitopes of cN-1A were frequent in patients with IBM (37%) but not in PM, DM or non-autoimmune neuromuscular diseases (<5%). Anti-cN-1A reactivity was also observed in some other autoimmune diseases, particularly Sjögrens syndrome (SjS; 36%) and systemic lupus erythematosus (SLE; 20%). Conclusions In summary, we found frequent anti-cN-1A autoantibodies in sera from patients with IBM. Heterogeneity in reactivity with the three immunodominant epitopes indicates that serological assays should not be limited to a distinct epitope region. The similar reactivities observed for SjS and SLE demonstrate the need to further investigate whether distinct IBM-specific epitopes exist.

Dense genotyping of immune-related loci in idiopathic inflammatory myopathies confirms HLA alleles as the strongest genetic risk factor and suggests different genetic background for major clinical subgroups

Objectives The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of rare autoimmune diseases characterised by muscle weakness and extramuscular manifestations such as skin rashes and interstitial lung disease. We genotyped 2566 IIM cases of Caucasian descent using the Immunochip; a custom array covering 186 established autoimmune susceptibility loci. The cohort was predominantly comprised of patients with dermatomyositis (DM, n=879), juvenile DM (JDM, n=481), polymyositis (PM, n=931) and inclusion body myositis (n=252) collected from 14 countries through the Myositis Genetics Consortium. Results The human leucocyte antigen (HLA) and PTPN22 regions reached genome-wide significance (p<5×10−8). Nine regions were associated at a significance level of p<2.25×10−5, including UBE2L3, CD28 and TRAF6, with evidence of independent effects within STAT4. Analysis of clinical subgroups revealed distinct differences between PM, and DM and JDM. PTPN22 was associated at genome-wide significance with PM, but not DM and JDM, suggesting this effect is driven by PM. Additional suggestive associations including IL18R1 and RGS1 in PM and GSDMB in DM were identified. HLA imputation confirmed that alleles HLA-DRB1*03:01 and HLA-B*08:01 of the 8.1 ancestral haplotype (8.1AH) are most strongly associated with IIM, and provides evidence that amino acids within the HLA, such as HLA-DQB1 position 57 in DM, may explain part of the risk in this locus. Associations with alleles outside the 8.1AH reveal differences between PM, DM and JDM. Conclusions This work represents the largest IIM genetic study to date, reveals new insights into the genetic architecture of these rare diseases and suggests different predominating pathophysiology in different clinical subgroups.

2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups

Objective To develop and validate new classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIM) and their major subgroups. Methods Candidate variables were assembled from published criteria and expert opinion using consensus methodology. Data were collected from 47 rheumatology, dermatology, neurology and paediatric clinics worldwide. Several statistical methods were used to derive the classification criteria. Results Based on data from 976 IIM patients (74% adults; 26% children) and 624 non-IIM patients with mimicking conditions (82% adults; 18% children), new criteria were derived. Each item is assigned a weighted score. The total score corresponds to a probability of having IIM. Subclassification is performed using a classification tree. A probability cut-off of 55%, corresponding to a score of 5.5 (6.7 with muscle biopsy) ‘probable IIM’, had best sensitivity/specificity (87%/82% without biopsies, 93%/88% with biopsies) and is recommended as a minimum to classify a patient as having IIM. A probability of ≥90%, corresponding to a score of ≥7.5 (≥8.7 with muscle biopsy), corresponds to ‘definite IIM’. A probability of <50%, corresponding to a score of <5.3 (<6.5 with muscle biopsy), rules out IIM, leaving a probability of ≥50 to <55% as ‘possible IIM’. Conclusions The European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria for IIM have been endorsed by international rheumatology, dermatology, neurology and paediatric groups. They employ easily accessible and operationally defined elements, and have been partially validated. They allow classification of ‘definite’, ‘probable’ and ‘possible’ IIM, in addition to the major subgroups of IIM, including juvenile IIM. They generally perform better than existing criteria.

Genome-wide association study identifies HLA 8.1 ancestral haplotype alleles as major genetic risk factors for myositis phenotypes.

Autoimmune muscle diseases (myositis) comprise a group of complex phenotypes influenced by genetic and environmental factors. To identify genetic risk factors in patients of European ancestry, we conducted a genome-wide association study (GWAS) of the major myositis phenotypes in a total of 1710 cases, which included 705 adult dermatomyositis, 473 juvenile dermatomyositis, 532 polymyositis and 202 adult dermatomyositis, juvenile dermatomyositis or polymyositis patients with anti-histidyl-tRNA synthetase (anti-Jo-1) autoantibodies, and compared them with 4724 controls. Single-nucleotide polymorphisms showing strong associations (P<5 × 10−8) in GWAS were identified in the major histocompatibility complex (MHC) region for all myositis phenotypes together, as well as for the four clinical and autoantibody phenotypes studied separately. Imputation and regression analyses found that alleles comprising the human leukocyte antigen (HLA) 8.1 ancestral haplotype (AH8.1) defined essentially all the genetic risk in the phenotypes studied. Although the HLA DRB1*03:01 allele showed slightly stronger associations with adult and juvenile dermatomyositis, and HLA B*08:01 with polymyositis and anti-Jo-1 autoantibody-positive myositis, multiple alleles of AH8.1 were required for the full risk effects. Our findings establish that alleles of the AH8.1 comprise the primary genetic risk factors associated with the major myositis phenotypes in geographically diverse Caucasian populations.

A Systems Based Investigation into Vitamin D and Skeletal Muscle Repair, Regeneration and Hypertrophy

Skeletal muscle is a direct target for vitamin D. Observational studies suggest that low 25[OH]D correlates with functional recovery of skeletal muscle following eccentric contractions in humans and crush injury in rats. However, a definitive association is yet to be established. To address this gap in knowledge in relation to damage repair, a randomised, placebo-controlled trial was performed in 20 males with insufficient concentrations of serum 25(OH)D (45 ± 25 nmol/l). Prior to and following 6 wk of supplemental vitamin D3 (4,000 IU/day) or placebo (50 mg of cellulose), participants performed 20 × 10 damaging eccentric contractions of the knee extensors, with peak torque measured over the following 7 days of recovery. Parallel experimentation using isolated human skeletal muscle-derived myoblast cells from biopsies of 14 males with low serum 25(OH)D (37 ± 11 nmol/l) were subjected to mechanical wound injury, which enabled corresponding in vitro studies of muscle repair, regeneration, and hypertrophy in the presence and absence of 10 or 100 nmol 1α,25(OH)2D3. Supplemental vitamin D3 increased serum 25(OH)D and improved recovery of peak torque at 48 h and 7 days postexercise. In vitro, 10 nmol 1α,25(OH)2D3 improved muscle cell migration dynamics and resulted in improved myotube fusion/differentiation at the biochemical, morphological, and molecular level together with increased myotube hypertrophy at 7 and 10 days postdamage. Together, these preliminary data are the first to characterize a role for vitamin D in human skeletal muscle regeneration and suggest that maintaining serum 25(OH)D may be beneficial for enhancing reparative processes and potentially for facilitating subsequent hypertrophy.

Genotyping of immune-related genetic variants identifies TYK2 as a novel associated locus for idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) may present as a primary autoimmune disorder, or overlap with other autoimmune/connective tissue diseases. The aetiology of IIM likely includes interactions between genetic and environmental factors. Several genetic variants common to multiple autoimmune disorders have been identified in recent genome-wide association studies (GWAS). A Myositis Genetics Consortium dermatomyositis (DM) GWAS also suggests genetic overlap with other autoimmune disorders.1 We sought to extend these findings to identify novel genetic risk factors in a large cohort of adult/juvenile patients with DM and polymyositis (PM), by genotyping immune-related single nucleotide polymorphisms (SNPs) not captured through the DM GWAS.1 SNPs significantly associated (p<5×10−8) with 10 autoimmune disorders (systemic lupus erythematosus, rheumatoid arthritis, juvenile idiopathic arthritis, coeliac disease, Crohns disease, ulcerative colitis, psoriasis, type 1 diabetes, multiple sclerosis and systemic sclerosis) were identified from published GWAS or the National Human Genome Research Institute GWAS catalogue.2 Unique SNPs were identified (n=233), of which 99 had not been directly genotyped or captured (r2≥0.8 with genotyped SNPs) through our DM GWAS.1 These 99 SNPs were genotyped using Sequenom in 1001 European Caucasian individuals with …

Myofibrillar activation failure in McArdle's disease

Contractile properties of the adductor pollicis muscle were examined in 9 normal volunteers and 7 patients with histochemically proven myophosphorylase deficiency (McArdles disease). Fatiguing contractions were produced by supramaximal stimulation of the ulnar nerve, delivered over a range of frequencies, to allow further examination of the mechanisms responsible for the premature fatigue in patients. The excessive reductions in force, demonstrated in patients at all frequencies, were not associated at high frequencies (50 and 100 Hz) with excessive declines in excitation (measured as compound muscle action potential). These results demonstrate that, in patients, myofibrillar activation failure occurs over and above that due to excitation failure. Abnormal slowing of relaxation mechanisms was also confirmed. These findings appear consistent with the hypothesis of inhibition of various ATPases by metabolic products. The observed, clear differences between normal subjects and myophosphorylase-deficient patients constitute the basis of an objective screening procedure for this and other glycolytic disorders.

The role of myokines in muscle health and disease.

Purpose of reviewThis article updates on the concept that muscle-derived cytokines (myokines) play important roles in muscle health and disease. Recent findingsInterleukin-6 (IL-6) is released from normal skeletal muscle in response to exercise, mediating both anti-inflammatory responses and metabolic adaptations, actions contradictory to the prevailing view that IL-6 is a proinflammatory cytokine that is inducing and propagating disease. The anti-inflammatory effects of IL-6 result from its trans-membrane signalling capability, via membrane-bound receptors, whereas its proinflammatory effects result instead from signalling via the soluble IL-6 receptor and gp130. IL-15 is elevated following exercise, promoting muscle fibre hypertrophy in some circumstances, while inducing fibre apoptosis in others. This functional divergence appears because of variations in expression of IL-15 receptor isoforms. Decorin, a recently described myokine, is also elevated following exercise in normal muscle, and promotes muscle fibre hypertrophy by competitively binding to, and thus inhibiting, myostatin, a negative regulator of muscle protein synthesis. Exercise-induced myostatin downregulation thus promotes muscle fibre growth, prompting recent trials of a biological myostatin inhibitor in inclusion body myositis. SummaryMyokines appear to exert diverse beneficial effects, though their mechanistic roles in myositis and other myopathologies remain poorly understood.

Understanding the origin of non-immune cell-mediated weakness in the idiopathic inflammatory myopathies - potential role of ER stress pathways.

Purpose of reviewDiscussion of endoplasmic reticulum (ER) stress pathway activation in idiopathic inflammatory myopathies (IIM), and downstream mechanisms causative of muscle weakness. Recent findingsIn IIM, ER stress is an important pathogenic process, but how it causes muscle dysfunction is unknown. We discuss relevant pathways modified in response to ER stress in IIM: reactive oxygen species (ROS) generation and mitochondrial dysfunction, and muscle cytokine (myokine) generation. First, ER stress pathway activation can induce changes in mitochondrial bioenergetics and ROS production. ROS can oxidize cellular components, causing muscle contractile dysfunction and energy deficits. Novel compounds targeting ROS generation and/or mitochondrial dysfunction can improve muscle function in several myopathologies. Second, recent research has demonstrated that skeletal muscle produces multiple myokines. It is suggested that these play a role in causing muscle weakness. Myokines are capable of immune cell recruitment, thus contributing to perturbed muscle function. A characterization of myokines in IIM would clarify their pathogenic role, and so identify new therapeutic targets. SummaryER stress pathway activation is clearly of etiological relevance in IIM. Research to better understand mechanisms of weakness downstream of ER stress is now required, and which may discover new therapeutic targets for nonimmune cell-mediated weakness.

2016 American College of Rheumatology/European League Against Rheumatism Criteria for Minimal, Moderate, and Major Clinical Response in Juvenile Dermatomyositis: An International Myositis Assessment and Clinical Studies Group/Paediatric Rheumatology International Trials Organisation Collaborative Initiative.

To develop response criteria for juvenile dermatomyositis (DM). We analysed the performance of 312 definitions that used core set measures from either the International Myositis Assessment and Clinical Studies Group (IMACS) or the Paediatric Rheumatology International Trials Organisation (PRINTO) and were derived from natural history data and a conjoint analysis survey. They were further validated using data from the PRINTO trial of prednisone alone compared to prednisone with methotrexate or cyclosporine and the Rituximab in Myositis (RIM) trial. At a consensus conference, experts considered 14 top candidate criteria based on their performance characteristics and clinical face validity, using nominal group technique. Consensus was reached for a conjoint analysis–based continuous model with a total improvement score of 0–100, using absolute per cent change in core set measures of minimal (≥30), moderate (≥45), and major (≥70) improvement. The same criteria were chosen for adult DM/polymyositis, with differing thresholds for improvement. The sensitivity and specificity were 89% and 91–98% for minimal improvement, 92–94% and 94–99% for moderate improvement, and 91–98% and 85–86% for major improvement, respectively, in juvenile DM patient cohorts using the IMACS and PRINTO core set measures. These criteria were validated in the PRINTO trial for differentiating between treatment arms for minimal and moderate improvement (p=0.009–0.057) and in the RIM trial for significantly differentiating the physicians rating for improvement (p<0.006). The response criteria for juvenile DM consisted of a conjoint analysis–based model using a continuous improvement score based on absolute per cent change in core set measures, with thresholds for minimal, moderate, and major improvement.