PHEX and hypophosphatemia: XLH features hypophosphatemia and reduced 1,25‐dihydroxyvitamin D levels, and both of these changes can directly affect ameloblast functions as shown by nutritional and genetic mouse studies.(3, 32, 33, 34) Ameloblasts have been reported to have low levels of PHEX protein localization,(35) though another study found no detectable Phex mRNA,(36) making the exact mechanism for enamel defects in XLH unclear.