Definition:

Primary immunodeficiency diseases (PIDs) are genetically determined disorders of the immune system resulting in greatly enhanced susceptibility to infectious disease, autoimmunity and malignancy. Many are associated with single gene defects, whereas others may be polygenic or may represent interactions of genetically determined characteristics with environmental or infectious stresses. There are more than 150 different disorders which have been described till date. PIDs are broadly classified as disorders of adaptive immunity (i.e., T-cell, B-cell or combined immunodeficiencies) or of innate immunity (e.g., phagocyte and complement disorders). Early diagnosis and treatment are imperative for preventing significant disease-associated morbidity.