Meningococcal meningitis in a woman with inherited deficiency of the ninth component of complement

Abstract A 17-year-old woman presented with acute pyogenic meningitis; Neisseria meningitidis group C was isolated from blood on culture. Complement assays demonstrated a hemolytic complement titer of 12 u/ml; individual components were normal except for C9, which was absent by both functional and antigenic analysis. Family studies were consistent with a familial C9 deficiency, autosomal co-dominant inheritance. This is the first report of the association of C9 deficiency and disseminated neisserial infection; whether this complement deficiency predisposes to the neisserial infection remains to be established.