Deletion of chromosome 22q11 and pseudohypoparathyroidism

Abstract

A newborn boy with complex congenital heart disease, unilateral renal agenesis, and hypocalcemia was found to have a submicroscopic deletion of 22q11.2 (DiGeorge anomaly). In evaluating the pathogenesis of the hypocalcemia, repeatedly elevated or normal levels of parathyroid hormone were found, consistent with a diagnosis of pseudohypoparathyroidism. Pseudohypoparathyroidism can be due to mutation of a GTP binding protein (Gs-α protein) located on chromosome 20. Since there is another G protein locus (Gz alpha) adjacent to the DiGeorge critical region of chromosome 22, we hypothesized that a more extensive deletion may lead to pseudohypoparathyroidism. Fluorescence in situ hybridization was performed using a probe containing the Gz alpha gene, but no deletion was detected. This patient emphasizes the importance of determining the pathogenesis of the hypocalcemia in cases of DiGeorge anomaly. Am. J. Med. Genet. 72:63–65, 1997. © 1997 Wiley-Liss, Inc.