Failure of development of the third and fourth pharyngeal pouches leads to absence of the thymus and parathyroids. There are also problems in development of the aortic arch and portions of the lips and ears.
This in turn leads to a lack of T-lymphocytes. There are also problems with calcium metabolism and facial abnormalities.
Most cases result from a deletion of chromosome 22q11.2. This deletion can result in a variety of phenotypes. These have collectively been described as CATCH-22 (Cardiac defects, Abnormal facies, T cell deficit due to thymic hypoplasia, Cleft palate, and Hypocalcaemia).
The condition was first described by Angelo DiGeorge.
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