Embryologic and other developmental considerations of thirty-eight possible variants of the DiGeorge anomaly.

The DiGeorge anomaly (DGA) represents a polytopic developmental field defect that can be caused by a number of different chromosomal, mendelian, toxic, or metabolic factors operating in early embryonic life. If the affected field is thought to be focused on either the fourth branchial arch or the third branchial pouch, with variable cephalad or caudad extension, 38 different combinations of malformations can include DiGeorge anomalies, 24 complete and 14 partial DGA, with the constraints that the field defect must be contiguous (involvement of more than one branchial arch or pouch requires involvement of all intervening arches or pouches) and complete (all derivatives of an affected branchial arch or pouch are deficient). The types and relative frequencies of abnormalities of structures other than the thymus and parathyroid glands in these possible "subsets" of DGA are discussed, and the need for more data on their occurrence in patients diagnosed as having DGA is emphasized.