DETECTION OF AUTOANTIBODIES AGAINST MUSCLE-SPECIFIC FOUR-AND-A-HALF-LIM DOMAIN 1 (FHL1) IN INFLAMMATORY MYOPATHIES: RESULTS FROM A SINGLE-CENTER COHORT

• Autoantibodies targeting a muscle-specific autoantigen, four-and-a-half-LIM-domain 1 (FHL1), have been previously identified in patients with idiopathic inflammatory myopathies (IIM) (1).Objectives:The aim of this project was to determine the prevalence and associations of anti-FHL antibody in South Australian patients with histologically-confirmed IIM and in an autoimmune disease control (systemic sclerosis (SSc)).Methods:Sera from patients with IIM (n=267) from the South Australian Myositis Database (SAMD), and SSc (n=174) from the Australian Scleroderma Cohort Study (ASCS) followed at the Royal Adelaide Hospital, and healthy controls (HC, n=100) were analyzed for anti-FHL1 autoantibodies by Enzyme-Linked ImmunoSorbent Assay (ELISA). Clinical, serological and histological details were retrieved from the SAMD and the ASCS.Results:Autoantibodies to FHL1 were more frequent in patients with IIM (55/267, 20.5%) compared with SSc (18/174, 10%) (p<0.001) and HC (4/100, 4%) (p<0.001). Muscular vessel inflammation and atrophy were seen more frequently in IIM anti-FHL1+ patients compared with anti-FHL1- (p<0.01 and p<0.05). Dysphagia, marked muscle atrophy, and high CK levels were frequent in anti-FHL1+ patients with inclusion body myositis (IBM) and immune-mediated necrotizing myopathy (IMNM). In 35/54 anti-FHL1+ patients, there were no other myositis-specific autoantibodies present. Anti-FHL1 autoantibodies in patients with SSc were associated with gastric antral vascular ectasia.Conclusion:Anti-FHL1 autoantibodies were detected in 20.5% of IIM patients. In IBM and IMNM, the presence of anti-FHL1-autoantibodies was associated with a severe myopathy as suggested by presence of dysphagia and muscle atrophy.References:[1]Albrecht I, Wick C, Hallgren A, Tjarnlund A, Nagaraju K, Andrade F, et al. Development of autoantibodies against muscle-specific FHL1 in severe inflammatory myopathies. J Clin Invest. 2015;125(12):4612-24.Disclosure of Interests:Angeles Shunashy Galindo-Feria: None declared, Begum Horuluoglu: None declared, Jessica Day: None declared, Catia Cerqueira: None declared, Susanna Proudman: None declared, Ingrid E. Lundberg Consultant of: Consulting fees from Corbus Pharmaceuticals, Inc, Grant/research support from: Research grants from Bristol Myers Squibb and Astra Zeneca, Vidya Limaye Consultant of: Scientific adviser for Actelion and Boehringer-Ingelheim, Grant/research support from: PI for clinical trials for Bayer, Boehringer-Ingelheim, Corbus, and CSL

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