<unk>  is an immunodeficiency of absent or suboptimal functioning of one of the complement system proteins.
The disorders can be divided into two categories:
Disorders of the proteins that act to inhibit the complement system (such as C1-inhibitor) can lead to an overactive response, causing conditions such as hereditary angioedema and hemolytic-uremic syndrome.
Disorders of the proteins that act to activate the complement system (such as C3) can lead to an underactive response, causing greater susceptibility to infections.
Because there are redundancies in the immune system, many complement disorders are never diagnosed. A recent study estimated that less than 10% are identified.
Complement deficiency
Complement deficiencies
IgG deficiency
Congenital defects of phagocytes
Natural killer cell deficiency
Leukocyte adhesion deficiency
Hyper-IgE syndrome
Primary immunodeficiency