Systemic lupus erythematosus associated with homozygous C2 deficiency. Apropos of a case report and literature review

: Inherited deficiencies of classical pathway complement components are rare and associated with autoimmune diseases and with increased susceptibility to bacterial infections. We report the clinical evolution and studies of the complement system in a 17-year-old female patient of Swiss origin presenting with systemic lupus erythematosus (malar rash, photosensitivity, leukopenia and antinuclear antibodies), in whom the hemolytically active second complement component (C2) was less than 10% of the normal value and antigenic C2 was not detectable. Linkage studies showed that the patient is HLA-A25, B18 positive and has the slow factor B allotype BfS. Further immunological assessment revealed low IgG4 concentrations in the patient, who had the G2M(23) allotype. The asymptomatic first degree family members had half-normal C2 levels compatible with a heterozygous state of C2 deficiency. Therapy with hydroxychloroquine for 17 months and topical sunscreen preparations produced marked clinical improvement. During the 4 years of follow-up, the patient has been well and shown only an abnormal titer of antinuclear antibodies. No infections were observed. To the best of our knowledge, 99 cases of homozygous C2 deficiency have been described so far and are discussed here.