Background Autoantibodies (Abs) against 5'-Nucleotidase, Cytosolic 1A (NT5C1A) have been portrayed as a potential diagnostic aide in distinguishing inclusion body myositis (IBM) and polymyositis (PM) in adults. However, 4–21% of dermatomyositis (DM) patients also have Abs to NT5C1A.
Objectives The prevalence and clinical features of anti-NT5C1A Abs in juvenile-onset myositis (IIM) patients is unknown, so we sought to examine this in a large cohort.
Methods We screened 384 juvenile IIM patients meeting probable or definite Bohan and Peter criteria for anti-NT5C1A Abs by immunoblotting for the full length NT5C1A protein in transfected and non-transfected lysates. Clinical characteristics and HLA typing were compared between juvenile IIM patients who were anti-NT5C1A positive (Ab+) and those who were anti-NT5C1A negative (Ab-).
Results In this cohort, 29% (103) of juvenile DM, 15% (3) of juvenile PM, and 37% (15) of juvenile overlap myositis patients tested positive for anti-NT5C1A Abs. Compared with anti-NT5C1A Ab- patients, anti-NT5C1A Ab+ juvenile IIM patients showed a similar distribution of race, gender, and association with myositis-specific Abs. However, NT5C1A Ab was associated with anti-p155/140 Abs (p=0.05). The only observed clinical difference was an increased frequency of V- or shawl-sign rashes ever present (44% vs. 26%, p=0.002). Disease severity was increased in anti-NT5C1A Ab+ patients, based on more frequent hospitalizations (p=0.02), more medications used (p<0.001), and more treatment trials per year (p<0.001). Additionally, pulse steroids (p<0.001) and intravenous immunoglobulin therapy (p=0.008) were prescribed more frequently in anti-NT5C1A Ab+ than Ab- patients. The HLA alleles DRB1*07 (20% vs. 9%, p<0.05) and DQA1*0201 (21% vs. 7%, p<0.01) were present more frequently in anti-NT5C1A Ab- compared to Ab+ patients.
Conclusions Anti-NT5C1A Abs are commonly present in juvenile DM and juvenile overlap myositis patients, and are present more frequently in patients with anti-p155/140 Abs, but are also seen in association with other myositis specific Abs. Consistent with data in adult IIM patients, anti-NT5C1A Abs have few distinguishing clinical features in juvenile myositis, but are associated with increased illness severity marked by increased hospitalizations and receipt of additional therapy.
Disclosure of Interest R. Yeker: None declared, I. Pinal-Fernandez Grant/research support from: The Myositis Association, T. Kishi Grant/research support from: The Myositis Association, I. Targoff Consultant for: Oklahoma Medical Research Foundation Clinical Immunology Laboratory regarding myositis autoantibody testing, F. Miller: None declared, L. Rider: None declared, A. Mammen: None declared