FGF23 and hypophosphatemic rickets: Previously, our group showed that the Sox2-Cre;Fam20Cflox/flox mice, in which Fam20C was inactivated in nearly all the tissues, suffered from hypophosphatemic rickets, along with an elevation of fibroblast growth factor 23 (FGF23) and a reduction of serum phosphorus in the serum13.