ABSTRACT
Neonatal severe hyperparathyroidism is a rare disorder arising from inherited defects in the calcium sensing receptor (CaSR) that presents early in life with severe hypercalcemia, failure to thrive, and developmental retardation. The authors describe an infant with neonatal severe hyperparathyroidism due to homozygous CaSR gene mutation presenting with recurrent episodes of severe hypercalcemia, growth retardation, and developmental delay. Medical management served as an efective bridge therapy to surgery. Total parathyroidectomy with right hemithyroidectomy was performed at 7 mo of age and resulted in successful cure and normalization of growth and developmental milestones. Timely medical and surgical management can help prevent mortality and morbidity in the form of neurodevelopmental sequelae. Life-long monitoring and treatment is mandatory for the resultant hypoparathyroidism.