Chapter 40 – Heritable Renal Phosphate Wasting Disorders

Heritable disorders leading to renal Pi wasting may be the most common cause of rickets in developed countries. However, the molecular mechanisms underlying the biochemical abnormalities and deranged bone/cartilage mineralization in these diseases are complex, and our current models remain incomplete. Isolated renal Pi wasting and consequent low serum Pi concentrations characterize several genetic disorders that include: autosomal dominant hypophosphatemic rickets (ADHR), X-linked hypophosphatemia (XLH), and autosomal recessive hypophosphatemic rickets (ARHR). They share a key central pathogenic role for the endocrine molecule called fibroblast growth factor 23 (FGF23). Understanding the interrelationships between these gene mutations and regulation of FGF23 production and proteolysis has provided obvious as well as new and unanticipated therapeutic targets for management of this constellation of diseases. Currently, the investigational anti-FGF23 monoclonal antibody (KRN23), called burosumab, is showing favorable results in XLH. These advances have come from ground-breaking studies in humans and animal models that will fuel further successful investigation.