Hypoparathyroidism is a clinical disorder characterized by hypocalcemia and hyperphosphatemia. It manifests when parathyroid hormone secreted from the parathyroid glands is insufficient to maintain normal extracellular fluid calcium concentrations or, less commonly, when PTH is unable to function optimally in target tissues, despite adequate circulating levels. Familial isolated hypoparathyroidism-1 (FIH1) is caused by heterozygous, homozygous, or compound heterozygous mutation in the parathyroid hormone gene.