| Abstract: | Complement system proteins, C4 metabolism and serologic markers of systemic lupus erythematosus were studied in identical male twins with chronic discoid lupus erythematosus and hereditary angioedema. Systemic lupus erythematosus was confirmed in their mother at age 22 during the twins' gestation. She also manifested symptoms suggesting hereditary angioedema. Low C1&;#x0304; inhibitor (C1&;#x0304; INH) and C4 have been documented since age 13 in both twins. At this time, metabolic studies disclosed a combined C4 fractional hypercatabolism (0.96 to 1.02/day) and decreased synthesis (3.0 to 3.15 mg /kg/day). Normal C1&;#x0304; inhibitor and C4 concentrations are present in their healthy father and maternal grandparents, indicating that the C1&;#x0304; inhibitor deficiency in the twins was inherited as an autosomal codominant from their mother in whom a spontaneous mutation had occurred. Positive antinuclear antibody, increased antibody to denatured deoxyribonucleic acid and immunoglobulin deposits in normal skin in both twins are evidence of systemic lupus erythematosus. In addition, a chronic biologic false-positive serology is present in one twin. We postulate that the association of hereditary angioedema and “familial” systemic lupus erythematosus is a biologically relevant phenomenon. It is proposed that the secondary C4 deficiency predisposed the patient to the development of systemic lupus erythematosus in some presently unknown manner. |
