In contrast to established causes of FIHP such as inactivated alleles of MEN1 or CDC73 (Table 3), the main GCM2 variants are found at much higher‐order frequencies in the general population(148, 149) with very limited data on their penetrance and with functional evidence only from in vitro transcriptional activity that heretofore is unlinked to the PHPT phenotype. This evidence concerns the gene GCM2 and familial isolated hyperparathyroidism.