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The Journey From Vitamin D–Resistant Rickets to the Regulation of Renal Phosphate Transport

Department of Medicine, VA Greater Los Angeles Healthcare System, and David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California

Correspondence: Dr. Arnold J. Felsenfeld,Nephrology Section (111L), West Los Angeles VA Medical Center, 11301 Wilshire Boulevard, Los Angeles, CA 90073. Phone: 310-268-4381; Fax: 310-268-4653; E-mail: arnold.felsenfeld{at}va.gov

In 1937, Fuller Albright first described two rare genetic disorders: Vitamin D resistant rickets and polyostotic fibrous dysplasia, now respectively known as X-linked hypophosphatemic rickets (XLH) and the McCune-Albright syndrome. Albright carefully characterized and meticulously analyzed one patient, W.M., with vitamin D–resistant rickets. Albright subsequently reported additional carefully performed balance studies on W.M. In this review, which evaluates the journey from the initial description of vitamin D–resistant rickets (XLH) to the regulation of renal phosphate transport, we (1) trace the timeline of important discoveries in unraveling the pathophysiology of XLH, (2) cite the recognized abnormalities in mineral metabolism in XLH, (3) evaluate factors that may affect parathyroid hormone values in XLH, (4) assess the potential interactions between the phosphate-regulating gene with homology to endopeptidase on the X chromosome and fibroblast growth factor 23 (FGF23) and their resultant effects on renal phosphate transport and vitamin D metabolism, (5) analyze the complex interplay between FGF23 and the factors that regulate FGF23, and (6) discuss the genetic and acquired disorders of hypophosphatemia and hyperphosphatemia in which FGF23 plays a role. Although Albright could not measure parathyroid hormone, he concluded on the basis of his studies that showed calcemic resistance to parathyroid extract in W.M. that hyperparathyroidism was present. Using a conceptual approach, we suggest that a defect in the skeletal response to parathyroid hormone contributes to hyperparathyroidism in XLH. Finally, at the end of the review, abnormalities in renal phosphate transport that are sometimes found in patients with polyostotic fibrous dysplasia are discussed.