GCM2 and familial isolated hyperparathyroidism: An increased prevalence of germline missense GCM2 variants is also reported in patients with apparently sporadic parathyroid adenomas, whilst certain FIHP and PHPT-associated GCM2 variants are enriched in individuals of specific ethnic background (e.g., Ashkenazi Jewish), and are likely associated with low disease penetrance.64,67 Genetic testing for each of the hereditary PHPT syndromes, FHH types 1-3, and GCM2 mutations should be considered in those with apparent FIHP to resolve diagnostic confusion (Figure 2).