PTH and hypercalcemia disease: Mutated mice showed hyperplastic enlarged parathyroids with increased cell proliferation, enhanced PTH secretion and hypercalcemia, and developed chronic PHPT with characteristic abnormalities in bone [38], providing evidence of a direct role of cyclin D1 over-expression in uncontrolled parathyroid cell proliferation and in hypercellularity-derived excessive release of PTH.