Genetic association study of NF-κB genes in UK Caucasian adult and juvenile onset idiopathic inflammatory myopathy.

OBJECTIVE: Treatment-resistant muscle wasting is an increasingly recognized problem in idiopathic inflammatory myopathy (IIM). TNF-α is thought to induce muscle catabolism via activation of nuclear factor-kappa B (NF-κB). Several genes share homology with the NF-κB family of proteins. This study investigated the role of NF-κB-related genes in disease susceptibility in UK Caucasian IIM. METHODS: Data from 362 IIM cases [274 adults, 49 (±14.0) years, 72% female; 88 juveniles, 6 (±3.6) years, 73% female) were compared with 307 randomly selected Caucasian controls. DNA was genotyped for 63 single nucleotide polymorphisms (SNPs) from NF-κB-related genes. Data were stratified by IIM subgroup/serotype. RESULTS: A significant allele association was observed in the overall IIM group vs controls for the IKBL-62T allele (rs2071592, odds ratio 1.5, 95% CI 1.21, 1.89, corrected P = 0.0086), which strengthened after stratification by anti-Jo-1 or -PM-Scl antibodies. Genotype analysis revealed an increase for the AT genotype in cases under a dominant model. No other SNP was associated in the overall IIM group. Strong pairwise linkage disequilibrium was noted between IKBL-62T, TNF-308A and HLA-B*08 (D' = 1). Using multivariate regression, the IKBL-62T IIM association was lost after adjustment for TNF-308A or HLA-B*08. CONCLUSION: An association was noted between IKBL-62T and IIM, with increased risk noted in anti-Jo-1- and -PM-Scl antibody-positive patients. However, the IKBL-62T association is dependent on TNF-308A and HLA-B*08, due to strong shared linkage disequilibrium between these alleles. After adjustment of the 8.1 HLA haplotype, NF-κB genes therefore do not independently confer susceptibility in IIM.

Paediatric idiopathic inflammatory muscle disease.

The paediatric idiopathic inflammatory myopathies (IIMs) are a group of rare but serious systemic autoimmune conditions of childhood. The most common of the paediatric IIMs is juvenile dermatomyositis (JDM), while polymyositis and inclusion body myositis are rare in children. JDM has a significantly different spectrum of disease from adult dermatomyositis. Juvenile myositis can also occur as part of other systemic autoimmune diseases such as scleroderma and systemic lupus erythematosus. There has recently been significant progress towards the development and validation of tools to measure disease activity and damage in the paediatric IIMs. In addition, several new therapeutic avenues have been used to treat JDM. This review will discuss developments in the diagnostic criteria for JDM, the clinical types and course of these conditions, recent progress in disease assessment, treatment options and new developments in research into the pathogenesis of paediatric IIM.

International consensus on a proposed score system for muscle biopsy evaluation in patients with juvenile dermatomyositis: a tool for potential use in clinical trials.

OBJECTIVE: To devise and test a system with which to evaluate abnormalities on muscle biopsy samples obtained from children diagnosed with juvenile dermatomyositis (DM). METHODS: We established an International Consensus Group on Juvenile DM Biopsy and carried out 2 phases of consensus process and scoring workshops. Biopsy sections (n = 33) were stained by standard methods. The scoring tool was based on 4 domains of change: inflammatory, vascular, muscle fiber, and connective tissue. Using a Latin square design, biopsy samples were scored by 11 experts for items in each domain, and for a global abnormality measure using a 10-cm visual analog score (VAS 0-10). The tool's reliability was assessed using an intraclass correlation coefficient (ICC) and scorer agreement (alpha) by determining variation in scorers' ratings. RESULTS: There was good agreement in many items of the tool, and several items refined between the meetings improved in reliability and/or agreement. The inflammatory and muscle fiber domains had the highest reliability and agreement. The overall VAS score for abnormality had high agreement and reliability, reaching an ICC of 0.863 at the second consensus meeting. CONCLUSION: We propose a provisional scoring system to measure abnormalities on muscle biopsy samples obtained from children with juvenile DM. This system needs to be validated, and then could be used in prospective studies to test which features of muscle pathology are prognostic of disease course or outcome. We suggest that the process we used could be a template for developing similar systems in other forms of myositis.

MHC Class I overexpression on muscles in early juvenile dermatomyositis.

OBJECTIVE: To assess muscle expression of MHC Class I complexes (heavy chain and beta2-microglobulin) and to analyze the composition of infiltrating mononuclear cells, specifically cells that bear receptors for class I MHC molecules, in the muscles of children with early juvenile dermatomyositis (JDM). METHODS: Light microscopic and immunohistochemical analysis of muscle biopsies from 10 patients with JDM and 3 controls. The mean duration from initial weakness was 2.8 months. At the time of biopsy, 9 patients had not received steroid treatment or immunomodulatory drugs. RESULTS: MHC Class I over-expression was evident on muscle fibers in all 10 JDM samples, even in a biopsy reported as normal by conventional histology. MHC class I heavy chain and beta2-microglobulin were over-expressed in an identical distribution. Variable infiltration of T cells and macrophages was seen in the JDM biopsies, with minimal lymphocytic and monocytic infiltration in 4 cases, and none in one. Only very occasional natural killer lymphocytes were identified. Neuronal cell adhesion molecule (NCAM, CD56) staining of regenerating muscle fibers was seen in all samples and these cells were confirmed as being of muscle origin by co-staining for dystrophin. CONCLUSION: MHC Class I over-expression is an early event in JDM, and may occur in the absence of lymphocytic infiltration and muscle damage. Immunostaining for MHC Class I could be used routinely in the assessment of muscle histology in juvenile dermatomyositis.