Congenital Athymia is an ultra-rare condition in which children are born without a thymus. The “T” in T cell stands for thymus because it is where T cells are selected to fight infections or are destroyed if they have the potential to attack the body instead of invaders. Without a thymus, children with congenital athymia may have profound immunodeficiency, vulnerability to potentially fatal infections, and life-threatening immune dysregulation. Congenital athymia is part of several syndromes, including 22q11.2 Deletion Syndrome, CHARGE Syndrome, and FOXN1 Deficiency.

With only supportive care, children with congenital athymia typically die by age two or three. Congenital athymia is initially detected by T-cell deficiency observed in newborn screening for SCID (severe combined immune deficiency), which is now required in all 50 U.S. states. SCID and congenital athymia are both primary immunodeficiency disorders but they are distinct conditions. The estimated incidence of pediatric congenital athymia in the United States is 17 to 24 live births each year.