Nezelof syndrome is one of many immunodeficiency disorders. Other names for Nezelof syndrome include Nezelof thymic aplasia, thymic dysplasia with normal immunoglobulins, combined immunodeficiency with immunoglobulins, pure alymphocytosis, Nezelof-type severe combined immunodeficiency, and immune defect due to the absence of the thymus. As with other immunodeficiency disorders, Nezelof syndrome is characterized by decreased ability of the individual to fight infections. Immunodeficiency in Nezelof syndrome is attributed to the absence of the thymus gland. The thymus gland, when present, is located in the neck and is critical to the function of the lymphatic system. Because T-lymphocytes are matured in the thymus gland, although immune factors (immunoglobulin) are present in the blood, there is an absence of T-cell function in Nezelof syndrome, and immune response is not present.