[Meningococcal meningitis in isolated familial deficiency of the 7th complement component, C7].

Based on recent reports of a hereditary disposition to neisserial infections in subjects deficient in one of the hemolytic components of the complement system, we have studied 2 siblings who had had "sporadic" meningococcal meningitis in 1976 and 1977 respectively. In neither was C7 detectable, which suggested a homozygous deficiency. The two children of the first propositus showed values compatible with a heterozygous state.