Terminal complement component deficiencies and rheumatic disease: development of a rheumatic syndrome and anticomplementary activity in a patient with complete C6 deficiency.

Hereditary deficiencies of early complement components have usually been associated with the development of rheumatic diseases like systemic lupus erythematosus (SLE), while terminal component deficiency is well known to predispose to recurrent neisserial infection. In contrast, only recently have patients been reported with rheumatic disease and hereditary deficiency of a terminal component. The clinical syndrome in these patients has been characterised as 'SLE-like'. We describe here a third patient with complete C6 deficiency and a systemic rheumatic illness characterised by fever, anaemia, lymphadenopathy, hepatosplenomegaly, episcleritis, and asymmetric arthritis. After blood transfusion her serum became anticomplementary; IgG antibody to human C6 was found to be the cause of anticomplement activity. Persistent absence of C6 in this patient and production of anti-C6 antibody after antigenic challenge indicate hereditary C6 deficiency. This case supports an association between hereditary deficiency of a terminal complement protein and the development of systemic rheumatic disease.