Dosage effect of a phex mutation in a murine model of X-linked hypophosphatemia

Shoji Ichikawa, Amie K. Gray, Emmanuel Bikorimana, Michael J. Econs

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

X-linked hypophosphatemia (XLH) is caused by mutations in the PHEX gene, which increase circulating levels of the phosphaturic hormone, fibroblast growth factor 23 (FGF23). Because XLH is a dominant disease, one mutant allele is sufficient for manifestation of the disease. However, the dosage effect of a PHEX mutation in XLH is not completely understood. To examine the effect of Phex genotypes, we compared serum biochemistries and skeletal measures between all five possible genotypes of a new murine model of XLH (Phex K496X or Phex Jrt ). Compared to sex-matched littermate controls, all Phex mutant mice had hypophosphatemia, mild hypocalcemia, and increased parathyroid hormone and alkaline phosphatase levels. Furthermore, mutant mice had markedly elevated serum Fgf23 levels due to increased Fgf23 expression and reduced cleavage of Fgf23. Although females with a homozygous Phex mutation were slightly more hypocalcemic and hypophosphatemic than heterozygous females, the two groups had comparable intact Fgf23 levels. Similarly, there was no difference in intact Fgf23 or phosphorus concentrations between hemizygous males and heterozygous females. Compared to heterozygous females, homozygous counterparts were significantly smaller and had shorter femurs with reduced bone mineral density, suggesting the existence of dosage effect in the skeletal phenotype of XLH. However, overall phenotypic trends in regards to mineral ion homeostasis were mostly unaffected by the presence of one or two mutant Phex allele(s). The lack of a gene dosage effect on circulating Fgf23 (and thus phosphorus) levels suggests that a Phex mutation may create the lower set point for extracellular phosphate concentrations.

Original languageEnglish (US)
Pages (from-to)155-162
Number of pages8
JournalCalcified Tissue International
Volume93
Issue number2
DOIs
StatePublished - Aug 1 2013

Keywords

  • Fgf23
  • Gene dosage effect
  • Phex
  • Phosphate
  • X-linked hypophosphatemia

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Endocrinology, Diabetes and Metabolism
  • Endocrinology

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