Systemic lupus erythematosus in a patient with C4 deficiency.

A 40-year-old female with systemic lupus erythematosus was found to be totally deficient in the 4th component of complement and to be lacking in Chido and Rodgers blood group substances on red cells and in plasma. Family studies were suggestive of a linkage of the C4 deficiency with an HLA haplotype. C2 in the patient's serum was 50% of normal but other complement components and alternative pathway functions were normal. Chemotactic and opsonic activities in the patient's serum were diminished.