In people with immune system disorders, the cause may be genetic defects, underlying diseases, drugs that suppresses the immune system, or autoimmune disorders where the body attacks its own tissue.
Doctors classify immune deficiencies into primary immune deficiencies (PIDs) and secondary immune deficiencies (SIDs). PIDs are a group of over 350 different immune system disorders in which genetic flaws in the cells and proteins of the immune system can cause it to stop working properly. The most common sign of having a PID is increased susceptibility to common infections, such as sinus and ear infections, common colds, bronchitis, fever and even pneumonia. Without treatment, such infections can be persistent and result in organ damage. In some cases, they can even be fatal. SIDs are caused by an underlying disease such as haematological cancer, or by a medical therapy that suppresses the immune system and leaves someone open to infection.
Immune thrombocytopenia (also known as ITP) is an autoimmune disorder causing internal bruising and an increased incidence of sometimes life-threatening internal bleeding. Bleeding occurs because the immune system attacks a certain type of cell, platelets which are needed to help control bleeding.
Chronic inflammatory demyelinating polyneuropathy (CIDP) is a rare neurological immune-mediated disorder affecting the peripheral nervous system. If left untreated, CIDP can lead to progressive motor and sensory dysfunction and permanent disability.
There are other forms of autoimmune disorders including, for example, Guillain-Barré syndrome (GBS) where the immune system attacks the nerves, and Kawasaki disease where malfunction of the immune system causes inflammation of the blood vessels.