Antibodies to small ubiquitin-like modifier activating enzyme are associated with a diagnosis of dermatomyositis: results from an unselected cohort.

The aim of this study was to examine the frequency and significance of antibodies targeting the small ubiquitin-like modifier 1 activating enzyme (SAE) in patients under serologic evaluation for idiopathic inflammatory myopathies. Patient sera (n = 17) recognizing bands at approximately 40 (SAE1) and 90 (SAE2) kDa were identified in 6445 consecutive samples for myositis autoantibody evaluation by immunoprecipitation (IP) of S35-labeled K562 cell lysate. All 17 positive samples, 176 disease, and 67 healthy controls were evaluated for SAE1 antibodies using a line immunoblot assay (LIA). Clinical data of SAE antibody-positive patients were obtained by retrospective chart review. Positivity with both methods was associated with a diagnosis dermatomyositis with characteristic skin manifestations of varying severity and muscle involvement. Majority of the patients were female (73.7%), mean age of 55.0 (range 12.0-82.0) years at the time of testing. Using the IP as reference, the SAE1 LIA had a sensitivity of 100% (95% CI 82.4-100%), specificity of 99.6% (95% CI 97.7-100%), positive predictive value of 95.0% (95% CI 75.1-99.9%), and negative predictive value of 100% (95% CI 98.5-100%). This study confirms the association of SAE antibodies in patients with dermatomyositis. A combination of IP and the LIA specific for SAE1 may be useful in antibody detection.