Thymic Deficiency in Down's Syndrome

Children with Down's syndrome (DS) often have small and abnormal thymuses, with lymphocyte depletion, diminution of the cortex, and loss of corticomedullary demarcation—a picture resembling thymic involution. Besides this, they have markedly enlarged Hassall's corpuscles, some surrounded by a sheath of lymphocytes. Patients with DS are known to have increased numbers of respiratory infections; they also have a higher incidence of lymphaic leukemia than do individuals who do not have DS. Studies of cell-mediated (thymic-dependent) immunity demonstrate that children with DS have both diminished numbers of T cells as well as functional deficiency of these cells.