Abstract

The clinical findings and genetic bases of inherited deficiencies of plasma complement components and complement control proteins are reviewed. In Japan, since the frequencies of late complement component deficiencies (LCCD) are high, clinical features of neisserial infections associated with LCCD are described in details. C9 deficiency is one of the most frequent genetic disorders in Japan and most of them are healthy. However, C9 deficiency is weakly but significantly associated with the development of meningococcal meningitis but not of systemic lupus erythematosus. The common Arg 95 Stop mutation was found in most individuals with C9 deficiency. Molecular epidemiologic study revealed that homozygous and heterozygous Arg 95 Stop mutation of C9 gene is found in approximately one of 1000 individuals and one of 15 individuals, respectively. Complement studies including C9 antigen and DNA analyses should be performed in patients with meningococcal meningitis or recurrent bacterial infections.