Genetic deficiencies of almost all the components of the complement system have been found in humans. The phenotype of these deficiencies tell us a good deal about the role of the complement system, though in the case of C1 INH it is complicated by the activity if C1 INH in inhibiting the serum proteases kallikrein and plasmin as well as C1s so that it's loss also dysregulates coagulation.
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