Dental Defects in XLH Patients and hyp Mice

X-linked hypophosphatemic vitamin D-resistant rickets (XLH) is caused by reduced renal tubular reabsorption of phosphate and characterized by growth retardation, skeletal abnormalities, and hypophosphatemia. Genetic defects underlying XLH have been identified as mutations in the phosphate-regulating gene which have homology to endopeptidases on the X chromosome (Phex) gene. The characteristic dental manifestation is the occurrence of gingival abscesses in the absence of an obvious cause such as dental caries or tooth fracture. Histopathological examination of teeth in the patients with XLH reveals evidence of poor mineralization in the dentin such as interglobular dentin, widened predentin, and tubular defects. The degree of occurrence of interglobular dentin was more severe in the XLH male tooth than in the female tooth. Objectives: In the present study, the effects of serum phosphate level on the formation of dentin were examined in hypophosphatemic (Hyp) mice. Methods: We gave a diet high in calcium and phosphate to Hyp mice for more than 10 days, which resulted in increase in serum phosphate level to that in normal mice. Results: when a high Ca/P diet was given to Hyp mice for 80 days, hypomineralized dentin was still present, while the transverse morphology of the incisor changed from triangle to round as the feeding period became longer. Conclusions: These results suggest that the hypo-mineralization of dentin that occurs in Hyp mice is not dependent on serum phosphate level alone.