The role of FGF23 was first identified in inherited conditions, such as X-linked hypophosphatemic rickets, autosomal dominant hypophosphatemic rickets and autosomal recessive hypophosphatemic rickets 1 and 2, caused by a loss-of-function of the following genes: phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX), dentine matrix protein 1 (DMP1) and ectonucleotide pyrophosphate/phosphodiesterase 1 (ENPP1), respectively [6]. Here, PHEX is linked to autosomal recessive hypophosphatemic rickets.