DiGeorge Syndrome (DGS) is a combination of signs and symptoms caused by defects in the development of structures derived from the pharyngeal arches during embryogenesis. Features of DGS were first described in 1828 but properly reported by Dr. Angelo DiGeorge in 1965, as a clinical trial that included immunodeficiency, hypoparathyroidism, and congenital heart disease.[1] DGS is one of several syndromes that has historically grouped under a bigger umbrella called 22q11 deletion syndromes, which include Shprintzen-Goldberg syndrome, velocardiofacial syndrome, Cayler cardiofacial syndrome, Sedlackova syndrome, conotruncal anomaly face syndrome, and DGS. Although the genetic etiology of these syndromes may be the same, varying phenotypes has supported the use of different nomenclature in the past, which has led to confusion in diagnosing patients with DGS, which causes potentially catastrophic delays in diagnosis.[2] Current literature supports the use of the names of these syndromes interchangeably. Features of DGS include an absent or hypoplastic thymus, cardiac abnormalities, hypocalcemia, and parathyroid hypoplasia (See "History and Physical" below). Perhaps, the most concerning characteristic of DGS is the lack of thymic tissue, because this is the organ responsible for T lymphocyte development. A complete absence of the thymus, though very rare and affecting less than 1% of patients with DGS, is associated with a form of severe combined immunodeficiency (SCID). T-cells are a differentiated type of white blood cell specializing in certain immune functions: destroying cells that are infected or malignant, existing as an integral part of the innate immune system by killing viruses (e.g., Killer T-cells), helping B-cells mature to produce immunoglobulins for stronger adaptive immunity (e.g. helper T-cells), etc. The degree of immunodeficiency of patients with DGS can present differently depending on the extent of thymic hypoplasia. Some patients may have a mild to moderate immune deficiency, and the majority of patients have cardiac anomalies. Other features include palatal, renal, ocular, and gastrointestinal anomalies. Skeletal defects, psychiatric disease, and developmental delay are also of concern. There are different opinions about syndrome-related alterations in cognitive development, and a cognitive decline rather than an early onset intellectual disability is observable.[3] The particularities of the clinical presentation requires observation on an individual basis, with careful evaluation and interprofessional treatment throughout the patient's life.