Complement deficiency describes a group of four disorders caused by a lack of one protein in the complement system. All of these disorders are caused by a genetic condition where one of the necessary proteins is missing or dysfunctional. This label describes conditions that both prevent the activation of certain parts of the immune system (immunodeficiency) and those that prevent the suppression of certain parts of the immune system (autoimmune). There are also conditions that can appear after the appearance of infection that fall within this group of disorders.
In over 90% of cases, the symptoms are so prosaic that no specific disorder can be identified, making this a zebra diagnosis. Moreover, because the immune system has built in redundancies, the condition is rarely life threatening.The vast majority of cases go undiagnosed. Moreover, the condition is rare, occuring in about one out of every ten thousand people.
Treatment focuses on relieving the patient's particular symptoms. Immunosuppressants are commonly used.