Discordance for X-Linked hypophosphataemic rickets in identical twin girls

Catherine J. Owen, Abdul Habeb, Simon H.S. Pearce, Michael Wright, Shoji Ichikawa, Andrea H. Sorenson, Michael J. Econs, Tim D. Cheetham

Research output: Contribution to journalArticle

5 Scopus citations


Background: We report monozygotic twin girls with a family history consistent with X-linked hypophosphataemic rickets (XLH). One twin had a skeletal and biochemical phenotype consistent with XLH, whilst the second twin appeared normal. Complete non-penetrance in XLH has not been previously reported and our aim was to explore potential reasons for this. Methods: Serum and urine biochemistry were analysed at regular intervals. Microsatellite analysis was performed to confirm monozygosity and bi-parental inheritance of the X chromosome. The X chromosome inactivation pattern was studied in peripheral blood. Exons of the paternal PHEX and FGF23 genes were sequenced. Results: Biochemistry was persistently abnormal in the slow-growing twin 1 and normal in twin 2 who has grown normally. Maximal tubular phosphate reabsorption was 0.68 mmol/l in twin 1 and 1.64 mmol/l in twin 2 at 10.8 years of age (normal 1.15-2.58 mmol/l). Microsatellite analysis confirmed monozygosity and the X chromosome inactivation pattern was random. These studies also excluded uniparental isodisomy. The exon sequence of paternal PHEX and FGF23 genes was normal. Conclusions: Discordant X inactivation is a well-recognised phenomenon in identical twins, and we suspect that non-random expression of the normal PHEX gene in critical tissues is the most likely explanation for non-penetrance.

Original languageEnglish (US)
Pages (from-to)237-244
Number of pages8
JournalHormone Research
Issue number4
StatePublished - Apr 2009


  • Monozygotic twins
  • X chromosome inactivation
  • X-linked hypophosphataemic rickets

ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

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    Owen, C. J., Habeb, A., Pearce, S. H. S., Wright, M., Ichikawa, S., Sorenson, A. H., Econs, M. J., & Cheetham, T. D. (2009). Discordance for X-Linked hypophosphataemic rickets in identical twin girls. Hormone Research, 71(4), 237-244. https://doi.org/10.1159/000201113