Missense mutations in the FGF23 consensus sequence or in GalNT3 and/or FAM20C have been shown to be detrimental to physiologic processes, where interfering with FGF23 cleavage results in either elevated serum intact FGF23 levels that results in hypophosphatemia, or diminished serum intact FGF23 levels which results in hyperphosphatemia due to excessive proteolytic cleavage [38,47,55,56,57,58,59]. The gene discussed is FGF23; the disease is hypophosphatemia.