Subsequent identification of FGF23 as the gene responsible for autosomal dominant hypophosphatemic rickets and of FGF23 overproduction in tumor-associated rickets led to the proposal that FGF23 might be the natural substrate for PHEX, and more generally to the recognition of a previously unsuspected FGF23-based phosphaturic regulation mechanism [11]. Here, FGF23 is linked to autosomal dominant hypophosphatemic rickets.