Prevalence of Sm antibody in family members of Sm positive patients with systemic lupus erythematosus.

Sm antibody is found almost exclusively in systemic lupus erythematosus (SLE). Considering Sm antibody to be a possible "marker" for SLE, we investigated the prevalence of Sm antibody in 29 first degree relatives and spouses of Sm positive patients with SLE. Sm antibody was not detected by Ouchterlony agar gel diffusion in any of the study group, and none of the family members or spouses had SLE or other antoimmune disease. This study suggests that Sm antibody is not a likely "marker" for a transmissable agent involved in the pathogenesis of SLE.