Thyrocalcitonin-containing cells in the Di George anomaly.

The Di George syndrome is an anomaly characterized by the complete or partial absence of derivatives of the third and fourth pharyngeal pouches often associated with defective development of the third, fourth, and sixth aortic arches leading to absence or hypoplasia of the thymus and parathyroid glands and to cardiovascular anomalies. The fifth pharyngeal pouch, often considered a part of the fourth pouch, gives rise to the ultimobranchial body (UB), which becomes incorporated into the thyroid gland and is thought to be the source of thyroid C cells. Robinson suggested that complete or partial absence of the UB should be considered a part of the Di George anomaly. To substantiate this theory, the thyroid glands of 11 patients with the Di George syndrome and 11 age-matched control infants were examined immunohistochemically using the immunoperoxidase technique for presence or absence of thyrocalcitonin (TC)-containing cells. Only three of 11 patients with the Di George syndrome had TC-containing cells in their thyroid glands (27 per cent), and nine of 11 control infants had these cells (82 per cent). It is concluded that thyroid C cell deficiency is present in most patients with Di George anomaly, suggesting a relationship between these cells and development of derivatives of the third through fifth visceral pouches. Furthermore, there is a spectrum of deficiency of thyroid C cells in these individuals comparable with the spectrum of partial to complete absence of third and fourth pharyngeal pouch derivatives regarding thymus and parathyroid glands. Immunostaining for TC of the lungs of all infants with the Di George syndrome and control infants revealed similar numbers of thyrocalcitonin-containing cells in both groups. Asynchronous development of thyroid and lung thyrocalcitonin-containing cells in those with the Di George syndrome favors the theory that the latter develop independently of derivatives of the third through fifth visceral pouches. This study further supports a neural crest origin of the Di George anomaly and strengthens the concept that the Di George anomaly is a neurocristopathy.