Germline mutations of genes, such as MEN1, CDC73, CDKN1B/p27, GCM2, and CASR, generate hereditary syndromes, namely, multiple neoplasia syndrome type 1 (OMIM#131100), primary hyperparathyroidism-jaw tumors (JT-HPT, OMIM#145000), multiple neoplasia syndrome type 4 (OMIM#610755), familial isolated hyperparathyroidism 4 (HRPT4; OMIM#617343), familial hypocalciuric hypercalcemia (HHC1; OMIM#145980), and neonatal severe hyperparathyroidism (NSHPT; OMIM#239200). Here, GCM2 is linked to neonatal severe primary hyperparathyroidism.