SNRNP70 and juvenile idiopathic arthritis: Myositis specific or associated autoantibodies were identified in 225 (59%) of patients in the myositis cohort but in none of the patients of the other disease groups (318 JIA, 21 JSLE, 27 muscular dystrophy) or healthy children, with the exception of the MAA anti-U1RNP which was found in 38% of JSLE patients.