Neonatal tetany is usually seen. There can be a right-sided aortic arch or tetralogy of Fallot. The absence of the thymus leads to deficiency in cell-mediated immunity, increasing susceptibility to infection. Diagnosis The T cell defect in children with congenital thymic hypoplasia varies from mild to profound. The lymph nodes lack paracortical lymphocytes.
Plasma cells are present, however, and the levels of immunoglobulins are normal.
Although patients with congenital thymic hypoplasia produce specific antibodies when they are immunized with various antigens, the antibody response is not quite normal, because secondary responses are lacking. As the patient ages, T cell function improves, and usually by the time the child is five years of age, no abnormality in cell-mediated immunity can be revealed by skin testing. Karyotyping reveals microdeletions at chromosome 22q11 in approximately 90 percent of patients. Treatment Thymus transplantation should be undertaken in those infants with congenital thymic hypoplasia who experience frequent infections. Transplantation of fetal thymus results in rapid acquisition of normal T cell function, which is thought to be secondary to production of a thymic hormone secreted by the thymic epithelium.