LATENT HYPOPARATHYROIDISM IN CHILDREN WITH CONOTRUNCAL CARDIAC DEFECTS

Background DiGeorge anomaly is characterized by hypoplasia or atresia of the thymus and parathyroid glands resulting in T cell-mediated immu ne deficiency, hypocalcemic hypoparathyroidism, and conotruncal cardia c defects. It usually is associated with deletions of chromosomal regi on 22q11. We hypothesized that the stimulated (secretory reserve) but not the constitutive secretion of parathyroid hormone would be reduced in normocalcemic children with conotruncal cardiac defects but no ove rt immune deficiency and would be related to the presence of a deletio n in the DiGeorge chromosomal region of 22q11. Methods and Results Blo od-ionized calcium and serum-intact parathyroid hormone were measured at baseline and seven more times during hypocalcemia induced during ca rdiopulmonary bypass in 22 patients and 10 control subjects with an at rial septal defect. Chromosomal deletions were detected by fluorescent in situ hybridization and DNA dosage analysis. There were no differen ces in basal calcium and parathyroid hormone levels between patients a nd control subjects. All had increased parathyroid hormone in response to hypocalcemia; despite lower calcium levels, parathyroid hormone le vels were lower in patients. The parathyroid hormone secretory reserve in 14 of 22 patients was reduced compared with control subjects; 4 of the 14 had deletions. Conclusions A significant number of children wi th conotruncal cardiac defects have normocalcemia and a normal constit utive level of parathyroid hormone but deficient parathyroid hormone s ecretory reserve; about 30% also have 22q11 deletions. Such children m ay be at risk for the later development of hypocalcemic hypoparathyroi dism.