Germline heterozygote activating mutations of the Glial Cells Missing Transcription Factor 2 (GCM2), encoding a transcription factor that acts as a master regulator of parathyroid development and may mediate the effect of calcium on PTH expression and secretion in parathyroid cells, were identified in FIHP probands by whole-exome sequencing, have been shown to co-segregate with the disease in affected members of the mutated FIHP families and confirmed in a prevalence-screening cohort of FIHP probands [7]. Here, HNF1B is linked to familial isolated hyperparathyroidism.