U1RNP positive neonatal lupus erythematosus: association with anti-La antibodies?

Neonatal lupus erythematosus (NLE) is an antibody-mediated disorder most commonly associated with autoantibodies to Ro and/or La antigens. There have been five previous reports describing eight NLE patients with anti-U1RNP antibody in the absence of anti-Ro and anti-La autoantibodies. We report two cases of anti-U1RNP antibody-positive NLE, and briefly review the five previous reports. The diagnosis of NLE was based on physical examination and serological studies by ELISA, immunodiffusion, and immunoblotting. By conventional immunodiffusion and ELISA, our cases were negative for anti-Ro and anti-La antibodies, and positive for anti-U1RNP antibody. However, one of the mothers had anti-La antibody detected by immunoblot assay only. All anti-U1RNP antibody-positive infants had classic cutaneous lesions of NLE, but it is of interest that none had congenital heart block (CHB). Although these infants were negative for anti-Ro and anti-La antibodies with immunodiffusion and ELISA techniques, these antibodies might be detectable by immunoblotting, as was the case in one of the mothers.