MDA5

Abstract: EDITORIAL article Front. Med., 31 May 2022Sec. Rheumatology https://doi.org/10.3389/fmed.2022.941370

Abstract: Purpose of review Antimelanoma differentiation antigen 5-dermatomyositis (MDA5-DM) is a complex and serious systemic autoimmune disease that primarily affects the skin and lungs. In this review, we aimed to provide new insights into the clinical features, pathogenesis, and practical management approach for this disease. Recent findings Although lung lesions are prominent in most patients with MDA5-DM, they are now recognized as heterogeneous diseases. Peripheral blood lymphocyte count can serve as a simple and reliable laboratory parameter for categorizing MDA5-DM into three subgroups: mild, medium, and severe. Recent studies have implicated viral infection, genetic factors, autoimmunity against MDA5, multiple immune cells, and interferons as significant contributors to MDA5-DM pathogenesis. In addition to traditional treatments with glucocorticoids and immunosuppressants, many new approaches, including new biologics and targeted agents, have been explored. Additionally, infection is a common complication of MDA5-DM, and prophylaxis or treatment of the infection is as important as treating the primary disease. Summary Knowledge of clinical characteristics and pathogenesis of MDA5-DM has grown in recent years. Although many new therapeutic approaches have been explored, further studies are required to confirm their efficacy.

Abstract: Abstract The IFIH1 gene, encoding melanoma differentiation‐associated protein 5 (MDA5), is an indispensable innate immune regulator involved in the early detection of viral infections. Previous studies described MDA5 dysregulation in weakened immunological responses, and increased susceptibility to microbial infections and autoimmune disorders. Monoallelic gain‐of‐function of the IFIH1 gene has been associated with multisystem disorders, namely Aicardi–Goutieres and Singleton–Merten syndromes, while biallelic loss causes immunodeficiency. In this study, nine patients suffering from recurrent infections, inflammatory diseases, severe COVID‐19 or multisystem inflammatory syndrome in children (MIS‐C) were identified with putative loss‐of‐function IFIH1 variants by whole‐exome sequencing. All patients revealed signs of lymphopaenia and an increase in inflammatory markers, including CRP, amyloid A, ferritin and IL‐6. One patient with a pathogenic homozygous variant c.2807+1G>A was the most severe case showing immunodeficiency and glomerulonephritis. The c.1641+1G>C variant was identified in the heterozygous state in patients suffering from periodic fever, COVID‐19 or MIS‐C, while the c.2016delA variant was identified in two patients with inflammatory bowel disease or MIS‐C. There was a significant association between IFIH1 monoallelic loss of function and susceptibility to infections in males. Expression analysis showed that PBMCs of one patient with a c.2016delA variant had a significant decrease in ISG15 , IFNA and IFNG transcript levels, compared to normal PBMCs, upon stimulation with Poly(I:C), suggesting that MDA5 receptor truncation disrupts the immune response. Our findings accentuate the implication of rare monogenic IFIH1 loss‐of‐function variants in altering the immune response, and severely predisposing patients to inflammatory and infectious diseases, including SARS‐CoV‐2‐related disorders.