Inherited C2 deficiency and systemic lupus erythematosus: studies on a family.

A patient is described in which an inherited defect in the synthesis of C2 complement component coexisted with the disease systemic lupus erythematosus. The family studies show evidence of the autosomal recessive nature of the inheritance of the C2 synthesis defect. Of particular interest was the finding of a great-aunt who also had homozygous C2 deficiency. This great-aunt suffered from discoid lupus erythematosus as well. The occurrence of various autoantibodies in the serum from the family members, the typing for blood groups, HL-A antigens, and some serum protein markers are reported and discussed. The C2 deficiency may be a critical defect in the host defenses to infection that predisposed to the development of autoimmune disease.