X-linked hypophosphatemic rickets and the murine Hyp homologue

K. A. Hruska, L. Rifas, S. L. Cheng, A. Gupta, L. Halstead, L. Avioli

Research output: Contribution to journalReview articlepeer-review

29 Scopus citations

Abstract

Recent studies have reported the cloning of several sodium-dependent phosphate cotransport proteins from the apical membrane of proximal tubules of several species. The human proximal tubule apical sodium-phosphate cotransport protein maps to chromosome 5 in the 5q35 region, indicating that this gene is not a candidate for the genetic defect leading to X-linked hypophosphatemia (XLH). Studies in what is thought to be the murine XLH homologue, Hyp, also indicate that the proximal tubular phosphate cotransporter gene does not map to the X chromosome. In Hyp, message levels for the apical membrane sodium cotransport protein are reduced by ~50%, similar to the reductions in the apical membrane protein levels of the transporter. This indicates a potential transcriptional defect in Hyp, leading to underexpression of the sodium-dependent phosphate transport protein. Recent studies in the Hyp osteoblast have characterized the intrinsic abnormalities of the cell leading to the osteomalacia characteristic of both Hyp and XLH. These studies demonstrate that the Hyp osteoblast expresses normal rates of phosphate transport, but altered gluconeogenesis similar to the proximal tubule, and that there is an underphosphorylation of an important matrix protein, osteopontin. Since osteopontin is involved in matrix mineralization, defective posttranslational modification of the protein could be a factor in producing the osteomalacia of the Hyp. Other recent studies have demonstrated improved modalities of treatment for Hyp and potentially for XLH. These involve the use of phosphate and nonhypercalcemic analogues of 1α,25-dihydroxyvitamin D3. Thus, although the detection of the genetic defect producing XLH and Hyp is awaited, significant advances in the characterization of the phenotype and the bone abnormalities continue.

Original languageEnglish
Pages (from-to)F357-F362
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Volume268
Issue number3 37-3
DOIs
StatePublished - 1995

Keywords

  • Hyp mouse
  • X-linked hypophosphatemia
  • casein kinase II
  • gluconeogenesis
  • osteomalacia
  • osteopontin
  • phosphorylation
  • sodium-phosphate cotransport

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