An<unk>  is a dysfunction of the<unk>  system. These disorders can be characterized in several different ways: * By the component(s) of the<unk>  system affected * By whether the<unk>  system is overactive or underactive * By whether the condition is congenital or acquired According to the International Union of<unk> logical Societies, more than 150 primary<unk> deficiency diseases (PIDs) have been characterized. However, the number of acquired<unk> deficiencies exceeds the number of PIDs. It has been suggested that most people have at least one primary<unk> deficiency. Due to redundancies in the<unk>  system, though, many of these are never detected.
Immune disorder
Autoimmune disease
Viral disease
Immunoproliferative disorder
Genetic disorder
Metabolic disorder
Psychogenic disease
Degenerative disease