U1—70‐kd autoantibody–positive mixed connective tissue disease in children. A longitudinal clinical and serologic analysis

OBJECTIVE: To obtain longitudinal data on the clinical, serologic, and immunogenetic features of children with mixed connective tissue disease (MCTD). METHODS: Eleven children with MCTD were followed up for a mean of 9.8 years. Enzyme-linked immunosorbent assay and immunoblotting were used to analyze sera for autoantibodies to small nuclear ribonucleoprotein polypeptides. HLA types were determined in 9 patients, by microcytotoxicity and DNA typing. RESULTS: All 11 children had anti-U1-70-kd auto-antibodies. Six of 9 were positive for HLA-DR2, 4 of 9 for HLA-DR4, and 9 of 9 for either HLA-DR2 or DR4. Outcomes were favorable with no functional impairment in 8 of the 11 children and were poor in 3. CONCLUSION: The frequency of HLA-DR2/DR4 is increased among children with anti-U1-70-kd autoantibody positive MCTD.