Urinary mercury levels in patients with autoantibodies to U3-RNP (fibrillarin)

Objective. Autoantibodies to the U3 nucleolar ribonucleoprotein (RNP) fibrillarin occur in some patients with systemic sclerosis (SSc) or other connective tissue diseases and can be induced in certain mouse strains by injections of mercuric chloride, perhaps due to antigenic alteration of fibrillarin by mercury (Hg). Thus, potential occult exposure to Hg was explored in patients with SSc. Methods. Urinary Hg levels were measured by cold vapor atomic absorption in 13 patients with antifibrillarin antibodies (11 with SSc), 39 SSc patients without antifibrillarin antibodies, and 32 healthy controls. Results. Mean urinary Hg levels were significantly elevated in the antifibrillarin antibody positive patients compared to those in other patients with SSc and controls. After correction for urinary creatinine levels, mean urinary Hg levels remained significantly different than in the other 2 groups, although Hg levels in all were still within the normal or 'unexposed' range. When patients and controls with low urinary creatinine levels were excluded from analysis, there were no significant differences in mean urinary Hg levels among the 3 groups. Conclusion. These findings suggest that further epidemiological and basic research studies of mercury are warranted in patients with SSc, especially those expressing antifibrillarin antibodies.