DiGeorge's syndrome in monozygotic twins. Treatment with calcitriol.

Monozygotic male twins with DiGeorge's syndrome had facial dysmorphism, cardiovascular abnormalities, hypocalcemia, and immunodeficiency; however, they showed differences in several aspects of this developmental complex. An early gestational insult, rather than a mutation, may be one cause of this heterogenous disorder. One twin had clinically appreciable hypoparathyroidism and had received calcitriol since early infancy. Despite close monitoring of therapy, he experienced two episodes of unexpected and prolonged hypercalcemia. Following the first episode, he was eucalcemic for nine weeks without therapy, attesting to the prolonged biological effects of calcitriol when used in the treatment of hypoparathyroidism.