Properdin deficiency

Properdin deficiency is a rare X-linked disorder of the immune system in which the complement protein properdin, which stabilises the alternative pathway C3 convertase, is missing, low or dysfunctional. It is described in three forms: type I, with no properdin protein in the plasma; type II, with a low but detectable amount; and type III, with a normal amount of a protein that does not work. The gene concerned, CFP, lies on the X chromosome and the condition is inherited as an X-linked recessive trait, so affected people are mostly male while carrier females may show partial deficiency without illness. It causes no outward physical signs. Its main effect is a heightened susceptibility to bacterial infection, above all with Neisseria species, which can lead to meningitis, sepsis and gonorrhoea, and occasionally recurrent pneumococcal bacteraemia. Early cases were studied in the 1980s, and the largest family study, by Fijen in 1989, followed nine affected males across three generations. Diagnosis rests on laboratory measurement of properdin, for which standard C3 and C4 tests are not sufficient, and a history of Neisseria infection. There is no cure; management treats it as an immune deficiency and relies on immunisation against the associated bacteria, with the caveat that the vaccine does not cover group B meningococci. This entry records what the sources state and is not medical advice.