Familial X-chromosome linked hypophosphatemic rickets: Report of a case

Abstract

Phosphorus is regulated by the kidney and bone system orchestrated mainly by the action of parathormone (PTH) and a molecule recently described as fibroblast growth factor 23 (FGF-23). We present the cases of two mother-son patients with X-linked hypophosphatemic rickets. Hypophosphatemic rickets is part of a group of tubulopathies characterized by hyperphosphaturia. A genetic study was performed, identifying a mutation in the PHEX gene (pathogenic splicing-type variant in hemizygosis), mutation previously described as HGMD CS126536. Loss-of-function mutation of the PHEX gene leads to increased FGF-23. PHEX degrades FGF-23 into inactive fragments, preventing excessive phosphate excretion and the development of hypophosphatemia. In a patient with hypophosphatemia not dependent on the hormone PTH or vitamin D and of familial presentation, the diagnosis of X-linked hypophosphatemic rickets should be considered.