Hereditary syndromes such as multiple endocrine neoplasias (MEN1, MEN2A, MEN4), familial hypocalciuric hypercalcemia (FHH), hyperparathyroidism jaw tumor (HPT-JT), and familial isolated primary hyperparathyroidism (FIPH) account for approximately 10% of cases of pHPT, with the remaining 90% occurring sporadically, usually as parathyroid adenomas [86]. Here, RET is linked to familial hypocalciuric hypercalcemia.