PTH and hyperinsulinemic hypoglycemia, familial, 4: Chronic hyperphosphatemia, hypocalcemia, and 1,25-dihydroxyvitamin D [1,25(OH)2D] deficiency are the primary factors that stimulate parathyroid hormone (PTH) synthesis and parathyroid cell proliferation, resulting in the autonomous hypersecretion of PTH and the development of hyperplastic parathyroid glands [2].