[A case of systemic lupus erythematosus in late component (C9) complement deficiency].

We report on a case of C9 deficiency followed by the onset of systemic lupus erythematosus (SLE). A 51-year-old female patient had suffered from repeated urinary tract infections since 1977. In 1980, at 41 years of age, she had proteinuria and facial erythema along with low level of CH50 less than 12.0 U/ml. She was diagnosed as C9 deficiency (C9D) because of C9 protein less than 0.5 mg/dl, C9 activity 0.03% and C8 activity 94% and also SLE was strongly suspicious. Subsequently, she suffered from repeated urinary tract infections. In 1990, she was diagnosed as SLE because of pleuritis, pericarditis and positive anti-nuclear (1:640) and positive anti-DNA antibody (28.0 U/ml) in addition to proteinuria and facial erythema. From the family study, her two sisters showed homozygous C9D (less than 0.5 mg/dl) with hypergammaglobulinemia (2290 and 2230 mg/dl, respectively) and positive anti-nuclear antibody (1:80) in both. Her father also showed heteropygous C9D (1.7 mg/dl) with anti-nuclear antibody (1:640). These results suggest that healthy carriers of C9D may have some abnormalities in humoral or cell-mediated immunity. The possibility was thought that other unrecognized disease associated loci exist in linkage with the C9 allele like that of C4D was speculated. And repeated infections due to C9D may possibly induce B cell activation followed by the occurrence of SLE or related disorders. This case seems to be very valuable with respect to the onset of SLE under a long-term observation of C9D.