The immune system is a complex network of cells and organs which cooperate to protect individual against infectious microorganisms, as well as internally-derived threats such as cancers. The immune system specializes in identifying danger, containing and ultimately eradicating it. It is composed of highly specialized cells, proteins, tissues, and organs. B- and T- lymphocytes, phagocytic cells and soluble factors such as complement are some of the major components of the immune system, and have specific critical functions in immune defense. When part of the immune system is missing or does not work correctly, immunodeficiency occurs; it may be either congenital (primary) or acquired (secondary). Secondary immunodeficiency diseases are caused by environmental factors such as infection with HIV, chemotherapy, irradiation, malnutrition, and others; while primary immunodeficiency diseases (PIDs) are hereditary disorders, caused by mutations of specific genes. Primary immunodeficiency diseases are a heterogeneous group of inherited disorders with defects in one or more components of the immune system. These diseases have a wide spectrum of clinical manifestations and laboratory findings; however, in the vast majority of cases, they result in an unusually increased susceptibility to infections and a predisposition to autoimmune diseases and malignancies . Primary immunodeficiencies constitute a large group of diseases, including more than conservatively defined hereditary disorders affecting development of the immune system, its function, or both .