[Clinical features and laboratory findings in children with both anti-dsDNA and anti-U1-RNP antibody].

Mixed connective tissue disease (MCTD) includes clinical features of systemic lupus erythematosus (SLE), dermatomyositis/polymyositis (DM/PM), and systemic sclerosis (SSc) occurring in conjunction with a high anti-U1-RNP antibody titer. Childhood MCTD rarely manifests the symptoms and signs of DM/PM and SSc, and mostly does those of SLE. Thus, the diagnosis of childhood MCTD is inevitably based on the two major findings, Raynaud's phenomenon and a high titer of anti-U1-RNP antibody. However, in clinical setting there exist patients who have both anti-dsDNA antibody, a SLE disease-marker, and anti-U1-RNP antibody, a MCTD disease-marker, and thus it is hard to differentiate MCTD patients from SLE. Eighty children were enrolled in this study, and divided into 3 groups ; group A, those who are positive for anti-dsDNA antibody/negative for anti-U1-RNP antibody (48 cases, 60.0%), group B : those who are positive for both anti-dsDNA and anti-U1-RNP antibody (22 cases, 27.5%), group C; those who are negative for anti-dsDNA antibody/positive for anti-U1-RNP antibody (10 cases, 12.5%), and each of the clinical characteristics among these 3 groups was mutually examined. The results indicated that the frequency of hypocomplementemia in group B was close to group A rather than group C, and the frequencies of both hyper-gamma-globulinemia and Raynaud's phenomenon were very close to group C, but not to group A. On the contrary, the findings which seemed to be specific to MCTD, high titers of speckled type anti-nuclear antibody and rheumatoid factor, located at the middle between group A and group C. Thus, children in group B essentially carried characteristic symptoms and signs of both SLE and MCTD, and it will be difficult to differentiate these two diseases at the onset of the disease. Taken together, children with high titers of both anti-dsDNA antibody and anti-U1-RNP antibody as well as clinical symptoms and signs such as hyper-gamma-globulinemia, Raynaud's phenomenon, membranous nephritis, positive speckled type anti-nuclear antibody and rheumatoid factor should be followed and treated as children with MCTD along with SLE.