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Genotype-phenotype correlations
Short report
Variant in C-terminal region of intestinal alkaline phosphatase associated with benign familial hyperphosphatasaemia
  1. Takayuki Ishige1,
  2. Sakae Itoga1,
  3. Emi Utsuno2,
  4. Motoi Nishimura1,2,
  5. Masaharu Yoshikawa3,
  6. Naoya Kato3,
  7. Kazuyuki Matsushita1,2,
  8. Osamu Yokosuka3,
  9. Fumio Nomura2
  1. 1 Division of Laboratory Medicine, Chiba University Hospital, Chiba, Japan
  2. 2 Division of Clinical Genetics, Chiba University Hospital, Chiba, Japan
  3. 3 Department of Gastroenterology and Nephrology, Graduate School of Medicine, Chiba University, Chiba, Japan
  1. Correspondence to Dr Takayuki Ishige, Division of Laboratory Medicine, Chiba University Hospital, Chiba 260-8677, Japan; ishige-t{at}chiba-u.jp

Abstract

Background A genetic diagnosis has been rarely performed in benign familial hyperphosphatasaemia, and molecular mechanism largely remains unclear.

Objectives We encountered a case with benign familial hyperphosphatasaemia of intestinal alkaline phosphatase (IAP). To elucidate the molecular mechanism, we performed ALPI gene sequencing and in vitro protein expression analysis.

Methods ALPI gene was sequenced by long-range PCR and massively parallel sequencing. The soluble and membrane-bound ALP activities of the cultured cell line, transfected with the wild-type or variant-type ALPI gene were analysed by a glycosylphosphatidylinositol (GPI)-cleaving assay.

Results We identified a deletion–insertion variant in the C-terminal end of the ALPI gene. This variant causes the attenuation of the hydrophobicity in GPI-anchor signal of IAP. An in vitro GPI-cleaving assay demonstrated that the membrane-bound IAP was greatly decreased, whereas the soluble IAP was increased, in the variant IAP.

Conclusions The C-terminal variant in ALPI causes the benign familial hyperphosphatasaemia of IAP by the attenuation of the membrane-binding capability.

  • diagnosis
  • gastroenterology
  • molecular genetics

https://doi.org/10.1136/jmedgenet-2017-104964

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    Footnotes

    • Contributors TI and FN were responsible for the study design. TI, SI, EU, MN and MY were responsible for the data collection and analysis. TI wrote the article. NK, KM, OY and FN were involved in the critical revision of the manuscript.

    • Funding This work was supported by JSPS KAKENHI, Grant Number 17K15768.

    • Competing interests None declared.

    • Ethics approval The study was approved by the Ethics Committee of Chiba University School of Medicine.

    • Provenance and peer review Not commissioned; externally peer reviewed.