Increased prevalence of autoantibodies to Ku antigen in African American versus white patients with systemic lupus erythematosus

Objective. To investigate whether the widely varying estimates of the preva lence of anti-Ku autoantibodies are explained by racial/ethnic differences. Methods. Consecutive African American or white patients who met the 1982 cr iteria for systemic lupus erythematosus (SLE) and who were evaluated over 1 0 years in North Carolina, Florida, and New York were tested by immunopreci pitation of K562 cell extract for anti-Ku as well as anti-nuclear RNP (nRNP )/Sm, anti-Ro/SSA, and anti-La/SSB autoantibodies. Results. Anti-Ku autoantibodies were detected in sera from 18 of 155 Africa n American patients with SLE (12%) versus 0 of 126 white patients (P < 0.00 01, by Fisher's exact test). Anti-nRNP (63% versus 16%; P < 0.0001) and ant i-Sm (23% versus 7%; P < 0.0004) autoantibodies were also more common in th e African American subset. The 2 groups had comparable frequencies of anti- Ro/SSA and anti-La/SSB autoantibodies. Conclusion. Anti-Ku antibodies are common in African American patients with SLE but rare in whites, probably explaining the different estimates of the ir prevalence. In African Americans, the frequency is comparable with that of anti-La/SSB. Along with anti-Ku, anti-nRNP and anti-Sm autoantibodies ar e also overrepresented in African Americans, suggesting that a group of spe cificities is characteristically associated with SLE in African Americans.