Because of its incomplete penetrance, patients with germline CDC73 mutation can present with a spectrum of phenotypes including seemingly sporadic parathyroid cancer (CDC73 PV/LPVs have been identified in 20–29% of parathyroid carcinomas), familial isolated hyperparathyroidism (FIHP) with or without parathyroid cancer, or full expression of hyperparathyroidism-jaw tumor syndrome (HPT-JT) [107, 108]. This evidence concerns the gene CDC73 and familial isolated hyperparathyroidism.