Congenital athymia (CA) is an ultra-rare condition in which the individuals are born without a functioning thymus. The thymus is responsible for controlling the development and maturation of T-cells, which are critical for protection against infection. Without a functioning thymus, individuals are profoundly immunodeficient, at significant increased susceptibility for infection, and greater tendency to develop autologous graft-versus-host disease (GVHD). Approximately 20 babies are diagnosed with CA annually in the United States. Without appropriate management, individuals with CA usually die before three (3) years of age due to fatal infection or autoimmune sequalae. Multiple genetic and syndromic disorders, mutations and deficiencies are associated with CA including: Forkhead Box Protein N1 (FOXN1) deficiency, 22q11.2 deletion, chromodomain helicase DNA binding protein 7 (CHD7) mutations, T Box transcription factor 1 and 2 (TBX1 and TBX2) mutations, CHARGE (Coloboma, Heart defects, Atresia of the nasal choanae, Retardation of growth and development, Genitourinary anomalies and Ear anomalies) Syndrome, and Complete DiGeorge Syndrome. Environmental factors such as diabetic embryopathy and exposure to retinoic acid have been found to be associated with CA as well.