The DiGeorge anomaly.

The DiGeorge anomaly, DGA (formerly termed DiGeorge syndrome), is now known to be a developmental field defect in which pharyngeal pouch derivatives do not arise, usually because of inadequate neural crest contributions. The conditions in which this occurs include exposure to teratogens, cytogenetic abnormalities, and Mendelian disorders. As a result, the facies and cardiovascular defects which occur are very characteristic. Two rare conotruncal anomalies, type B interrupted aortic arch and truncus arteriosus account for over half of the cardiac lesions seen in DGA. Failure of descent of the thymus is extremely common in DGA, but immunodeficiency which requires correction occurs only in approximately 25% of the cases. The term, complete DGA, should be reserved for those patients in need of reconstitution of the immune system. One can identify those patients requiring treatment of the thymic defect by T cell enumeration and in vitro proliferation assays. Two alternatives for therapy are thymus transplantation and bone marrow transplantation from a HLA matched sibling.