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What is Thymic hypoplsia is seen in which of the following and explain in detail?
Ref Robbins 9/e p224 Thymic Hypoplasia: DiGeorge Syndrome DiGeorge syndrome results from a congenital defect in thymic development with deficient T cell maturation. T cells are absent in the lymph nodes, spleen, and peripheral blood, and infants with this defect are extremely vulnera- ble to viral, fungal, and protozoal infections. Patients are also susceptible to infection with intracellular bacteria, because of defective T cell-mediated immunity. B cells and serum immunoglobulins are generally unaffected. The disorder is a consequence of a developmental mal- formation affecting the third and fouh pharyngeal pouches, structures that give rise to the thymus, parathy- roid glands, and poions of the face and aoic arch. Thus, in addition to the thymic and T cell defects, there may be parathyroid gland hypoplasia, resulting in hypocalce- mic tetany, as well as additional midline developmental abnormalities. In 90% of cases of DiGeorge syndrome there is a deletion affecting chromosomal region 22q11, as discussed in Chapter 6. Transplantation of thymic tissue has successfully treated some affected infants. In patients with paial defects, immunity may improve spontane- ously with age.