FGF23 and hypophosphatemic rickets: Thus, intact FGF23 is stabilized through O‐glycosylation on Thr178 by GALNT3;(96) it can be cleaved by the serine endoprotease furin at S180 to form the cleaved peptide, which is thought to be inactive and/or inhibitory.(96) Humans that lack the ability to cleave FGF23 develop hypophosphatemic rickets (autosomal dominant or X‐linked).(95) One of the receptors for FGF23, FGFR1c, may also be involved with phosphate sensing through intracellular phosphorylation, independent of ligand.(98) In the kidney, FGF23 acts to promote phosphate excretion.