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Abstract Complement proteins are deposited in the muscles of patients with myositis. However, the local expression and regulation of complement genes within myositis muscle have not been well characterized. In this study, bulk RNA sequencing (RNAseq) analyses of muscle biopsy specimens revealed that complement genes are locally overexpressed and correlate with markers of myositis disease activity, including the expression of interferon-gamma (IFNγ)-induced genes. Single cell and single nuclei RNAseq analyses showed that most local expression of complement genes occurs in macrophages, fibroblasts, and satellite cells, with each cell type expressing different sets of complement genes. Biopsies from immune-mediated necrotizing myopathy patients, who have the lowest levels of IFNγ-induced genes, also had the lowest complement gene expression levels. Furthermore, data from cultured human cells showed that IFNγ upregulates complement expression in macrophages, fibroblasts, and muscle cells. Taken together, our results suggest that in myositis muscle, IFNγ coordinates the local overexpression of complement genes that occurs in several cell types.

Background: Myositis, or idiopathic inflammatory myopathy (IIM), is a group disorders of unknown etiology characterized by the inflammation of skeletal muscle. The role of T cells and their antigenic targets in IIM initiation and progression is poorly understood. T cell receptor (TCR) repertoire sequencing is a powerful approach for characterizing complex T cell responses. However, current TCR sequencing methodologies are complex, expensive, or both, greatly limiting the scale of feasible studies. Methods: Here we present Framework Region 3 AmplifiKation sequencing (“FR3AK-seq”), a simplified multiplex PCR-based approach for the ultra-efficient and quantitative analysis of TCR complementarity determining region 3 (CDR3) repertoires. By using minimal primer sets targeting a conserved region immediately upstream of CDR3, undistorted amplicons are analyzed via short read, single-end sequencing. We also introduce the novel algorithm Inferring Sequences via Efficiency Projection and Primer Incorporation (“ISEPPI”) for linking CDR3s to their associated variable genes. Findings: We find that FR3AK-seq is sensitive and quantitative, performing comparably to two different industry standards. FR3AK-seq and ISEPPI were used to efficiently and inexpensively characterize the T cell infiltrates of surgical muscle biopsies obtained from 145 patients with IIM and controls. A cluster of closely related TCRs was identified in samples from patients with sporadic inclusion body myositis (IBM). Interpretation: The ease and minimal cost of FR3AK-seq removes critical barriers to routine, large-scale TCR CDR3 repertoire analyses, thereby democratizing the quantitative assessment of human TCR repertoires in disease-relevant target tissues. Importantly, discovery of closely related TCRs in muscle from patients with IBM provides evidence for a shared antigen-driven T cell response in this disease of unknown pathogenesis. Funding: This work was supported by NIH grant U24AI118633 and a Prostate Cancer Foundation Young Investigator Award.

Abstract Background The screening of high-risk populations using dried blood spots (DBS) has allowed the rapid identification of patients with Pompe disease, mostly in Neurology departments. The aim of the study was to determine the prevalence of late-onset Pompe disease (LOPD) among patients not previously diagnosed or tested for this entity despite presenting possible signs or symptoms of the disease in Internal Medicine departments in Spain. Methods This epidemiological, observational, cross-sectional, multicenter study included a single cohort of individuals with clinical suspicion of LOPD seen at Internal Medicine departments in Spain. The diagnosis of LOPD was initially established on the basis of the result of DBS. If decreased enzyme acid-alpha-1,4-glucosidase (GAA) activity was detected in DBS, additional confirmatory diagnostic measurements were conducted, including GAA activity in lymphocytes, fibroblasts, or muscle and/or genetic testing. Results The diagnosis of LOPD was confirmed in 2 out of 322 patients (0.6%). Reasons for suspecting LOPD diagnosis were polymyositis or any type of myopathy of unknown etiology (in one patient), and asymptomatic or pauci-symptomatic hyperCKemia (in the other). The time between symptom onset and LOPD diagnosis was 2.0 and 0.0 years. Both patients were asymptomatic, with no muscle weakness. Additionally, 19.7% of the non-LOPD cases received an alternative diagnosis. Conclusions Our study highlights the existence of a hidden population of LOPD patients in Internal Medicine departments who might benefit from early diagnosis and early initiation of potential treatments.

Dermatomyositis is a systemic vasculopathy mainly affecting skin, muscle and lung, but may affect the gastrointestinal tract. We aim to describe clinical characteristics of patients with severe gastrointestinal involvement related to dermatomyositis in our center and medical literature. We retrospectively analysed these patients in our center, including cases of erosions/ulcers, perforation or digestive bleeding. Reported cases from April 1990 to April 2021 were reviewed through PubMed and Cochrane. From our cohort (n = 188), only 3 presented gastrointestinal compromise. All were women (10, 46 and 68 years). The initial symptom was abdominal pain and all had ≥2 episodes of digestive bleeding. All died due to complications of gastrointestinal involvement. Available pathological samples showed vascular ectasia. From the literature review (n = 50), 77% were women with a mean age of 49 years and the main symptom was abdominal pain (65%). All presented active muscular and cutaneous involvement at complication diagnosis. Mortality was 41.7%. The underlying lesion was perforation or ulcer (n = 22), intestinal wall thickening (n = 2), macroscopic inflammation (n = 2) or intestinal pneumatosis (n = 15). In 13 cases, vasculitis was described. Gastrointestinal involvement in dermatomyositis denotes severity, so an early intensive treatment is recommended. Pathological findings suggest that the underlying pathophysiological mechanism is a vasculopathy and not a true vasculitis.