Hereditary deficiency of the third component of complement in two sisters with systemic lupus erythematosus-like symptoms.

We observed two sisters with lupus-like syndrome with homozygous C3 deficiencies. A 19-year-old woman and her 15-year-old sister developed malar rash, arthralgia, and photosensitivity, but antinuclear antibodies and LE cell preparations were negative. The older sister experienced recurrent bronchitis in her childhood, but the younger sister had no recurrent infections. Serum C3 was not detected immunochemically in either sister, and total complement activity and C3 hemolytic activity were extremely low.