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Discordance for X-Linked Hypophosphataemic Rickets in Identical Twin Girls

Lookup NU author(s): Dr Kate Owen, Professor Simon PearceORCiD, Dr Michael Wright, Professor Timothy Cheetham


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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.

Publication metadata

Author(s): Owen CJ, Habeb A, Pearce SH, Wright M, Ichikawa S, Sorenson AH, Econs MJ, Cheetham TD

Publication type: Article

Publication status: Published

Journal: Hormone Research

Year: 2009

Volume: 71

Issue: 4

Pages: 237-244

ISSN (print): 1663-2818

ISSN (electronic): 1663-2826

Publisher: S. Karger AG


DOI: 10.1159/000201113


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Funder referenceFunder name
G84/5959Medical Research Council