The syndromic forms of PHPT are due to LOF of tumor suppressor genes, e.g., MEN1, CDKN1B, and CDC73, with patients harboring germline CDC73 mutations having a higher occurrence of parathyroid carcinomas [23, 26] or increased oncogenic signaling (e.g., activating RET mutations; Table 1). This evidence concerns the gene MEN1 and parathyroid gland carcinoma.