Hereditary C2 deficiency in systemic lupus erythematosus and acquired complement abnormalities in an unusual SLE-related syndrome.

Early study of kindreds with C2 deficiency indicated that absence of C2 had no detrimental effect on affected individuals. Studies of additional kindreds, however, show a high incidence of SLE and other connective tissue diseases among homozygous C2-deficient members. A group of patients with an unusual SLE-related syndrome is described. In common with certain SLE patients they have marked depression of early complement components and presence of circulating Clq precipitins. It is suggested that early complement components are involved in specific host defense mechanisms and deficiencies of these components may predispose to such diseases.