DiGeorge’s syndrome (Thymic Aplasia)
DiGeorge’s syndrome (DGS) is secondary to a hemizygous deletion of the short arm of chromosome 22 (DEL 22q.11.2). This chromosomal defect causes a complex inherited syndrome characterized by cardiac malformations, thymic hypoplasia, palatopharingeal abnormalities with associated velopharingeal abnormalities with associated velopharingeal dysfunction, hypoparathyroidism, and facial dysmorphism. The 22q deletion has an incidence of approxymately 1 in 2500 live births. The associated clinical phenotype is highly variable. About 20% of individuals with 22q deletion have thymic aplasia, resulting in T lymphopenia and impaired CMI. In most such cases, the degree of T lymphopenia is modest (partial DGS) and almost complete restitution of the T cell repertoire and function occurs by two years of age. Therefore, infections characteristic of T-cell deficiency are rare in these individuals. A minority of infected individuals (<1 percent) exhibit profound T lymphopenia, associated with opportunistic infections and a poor outlook unless rescued with fetal thymic transplant.