Primary immunodeficiency disease: A disorder caused by an inherited flaw in the immune system that increases the susceptibility to infections. Primary immunodeficiency diseases are unlike secondary or acquired immune deficiency diseases, which are caused by infectious, chemical or radiological agents. AIDS is a prototype of an acquired immune deficiency disease.
It has been estimated that there are 100 different primary immunodeficiency diseases. All are genetic conditions in which specific cells of the immune system do not function properly. Clinical symptoms range from mild or nonexistent as in the case of selective IgA deficiency to severe symptoms as in the case of severe combined immunodeficiency (SCID), commonly referred to as "bubble-boy" syndrome.
Although the susceptibility to infections is a major consequence of the primary immunodeficiency diseases, they may cause other health problems as well, including allergies, asthma, swollen joints, digestive tract problems, growth problems or an enlarged liver and spleen. Many people with primary immune deficiency diseases require treatment which may include intravenous gamma globulin infusions, antibiotic therapies, or bone marrow transplantation.
The primary immune deficiency disorders range in frequency. Some disorders such as selective IgA deficiency are quite common, occurring as often as 1/500 to 1/1000 individuals. Others disorders such as SCID are rare affecting perhaps one person per million. Approximately 25,000 to 50,000 Americans are severely affected by primary immune deficiency disorders.