GCM2 and familial isolated hyperparathyroidism: Non-syndromic hereditary hyperparathyroidism, called familial isolated hyperparathyroidism (FIHP), can be caused by the incomplete manifestation of mutations of syndrome-related genes such as MEN-1, CDC73, GCM2, CDKN1A, CDKN1B, or CDKN2C [17,21].