Genetic Deficiencies of the Complement System

Genetic deficiencies of almost all the 20 proteins of the complement system have been described. They are all inherited as autosomal recessive phenomena with the exception of properdin (X-linkage) and CI 1NH (autosomal dominant). The deficiencies readily fall into five categories that are distinctive but not without overlap. They present with angio-oedema (CI 1NH); immune complex disease (Clq, Or, C4, C2); susceptibility to pyogens (C3, factor H, factor I) or Neisseria (C5, C6, C7, C8, properdin). C9-deficient individuals appear to be mostly asymptomatic. Rapid progress is being made in understanding the molecular biology of these deficient states.