A complete selective C1q deficiency in a patient with discoid lupus erythematosus (DLE).

A 32 year old male patient with discoid lupus erythematosus (DLE) was found to have a complete, selective deficiency of C1q subcomponent of the complement assessed either by haemolytic assay or by protein determination. Addition of highly purified C1q completely restored the complement haemolytic activity of the patient's serum. Neither C1q precipitin nor anti-complementary activity was detected. Lymphocytes isolated from the patient's peripheral blood, however, bound as many C1q molecules as those of healthy control individuals. The patient is in good health except for skin lesions. A low level of circulating immune complexes was detected in his serum, but no C1q molecules were bound. Serum complement activities of the patient's mother and two other siblings were within the normal range. An impaired synthesis of C1q protein was strongly suggested as the cause of C1q deficiency in this patient's serum.