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 prevalence of anti‐Ku autoantibodies are explained by racial/ethnic differences. Methods Consecutive African American or white patients who met the 1982 criteria for systemic lupus erythematosus (SLE) and who were evaluated over 10 years in North Carolina, Florida, and New York were tested by immunoprecipitation 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 African American patients with SLE (12%) versus 0 of 126 white patients (P < 0.0001, by Fisher's exact test). Anti‐nRNP (63% versus 16%; P < 0.0001) and anti‐Sm (23% versus 7%; P < 0.0004) autoantibodies were also more common in the 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 their prevalence. In African Americans, the frequency is comparable with that of anti‐La/SSB. Along with anti‐Ku, anti‐nRNP and anti‐Sm autoantibodies are also overrepresented in African Americans, suggesting that a group of specificities is characteristically associated with SLE in African Americans.