Identification of a p.Trp403* nonsense variant in PHEX causing X-linked hypophosphatemia by inhibiting p38 MAPK signaling

Hum Mutat. 2019 Jul;40(7):879-885. doi: 10.1002/humu.23743. Epub 2019 Mar 28.

Abstract

X-linked hypophosphatemia (XLH) is the most common hereditary rickets, caused by mutations in PHEX encoding the phosphate regulating endopeptidase homolog X-linked. Here, we report a nonsense variant in exon 11 of PHEX (c.1209G>A p.Trp403*) cosegregating with XLH in a Chinese family with a LOD score of 2.70. Real-time reverse transcription polymerase chain reaction analysis demonstrated that p.Trp403* variant did not cause nonsense-mediated mRNA decay (NMD), but significantly increased the expression level of FGF23 mRNA in the patients. Interestingly, p.Trp403* significantly reduced phosphorylation of p38 mitogen-activated protein kinase (MAPK) but not ERK1/2. Moreover, overexpression of FGF23 significantly decreased phosphorylation of p38 MAPK, whereas knockdown of FGF23 by siRNA significantly increased phosphorylation of p38 MAPK. These data suggest that p.Trp403* may not function via an NMD mechanism, and instead causes XLH via a novel signaling mechanism involving PHEX, FGF23, and p38 MAPK. This finding provides important insights into genetic and molecular mechanisms for the pathogenesis of XLH.

Keywords: ERK1/2; FGF23; PHEX; X-linked hypophosphatemia; p38 MAPK.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Codon, Nonsense
  • Familial Hypophosphatemic Rickets / genetics*
  • Familial Hypophosphatemic Rickets / metabolism
  • Female
  • Fibroblast Growth Factor-23
  • Fibroblast Growth Factors / genetics*
  • Genetic Predisposition to Disease
  • Humans
  • MAP Kinase Signaling System
  • Male
  • PHEX Phosphate Regulating Neutral Endopeptidase / genetics*
  • Pedigree
  • Phosphorylation
  • Point Mutation*
  • Up-Regulation
  • p38 Mitogen-Activated Protein Kinases / metabolism*

Substances

  • Codon, Nonsense
  • FGF23 protein, human
  • Fibroblast Growth Factors
  • Fibroblast Growth Factor-23
  • p38 Mitogen-Activated Protein Kinases
  • PHEX Phosphate Regulating Neutral Endopeptidase
  • PHEX protein, human