Detailed investigations of proximal tubular function in Imerslund-Gräsbeck syndrome

BMC Medical Genetics

Renata Kozyraki²  Erik I Christensen⁹  Rikke Nielsen⁹  Jens Michael Hertz¹  Heidi Koldsø⁶  Francesco Emma⁷  Iben Møller Jønsson⁸  Sophie Lebon⁴  Sandrine Passemard⁴  Jean-François Benoist⁵  Mette Madsen⁹  Pierre J Verroust³  Sabine Amsellem³  Olivier Cases³  Christina Zeitz³  Tina Storm⁹ 

[1] Department of Clinical Genetics, Odense University Hospital, Odense, Denmark;Service de Biochimie B, Hôpital Saint-Antoine, Paris, France;CNRS, UMR_7210, Paris, F-75012, France;Inserm U676, Hôpital Robert Debré, Paris, France;Laboratoire de Biochimie, Hôpital Robert Debré, Paris, France;Centre for Insoluble Protein Structures (inSPIN) and Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Aarhus, Denmark;Department of Nephrology and Urology, Division of Nephrology and Dialysis, Ospedale Bambino Gesù, IRCCS, Rome, Italy;Department of Pediatrics, Aarhus University Hospital, Aarhus, Denmark;Department of Biomedicine, Aarhus University, Aarhus, Denmark

关键词: Tubular proteinuria;    Proximal tubules;    Amnionless;    Cubilin;    Imerslund-Gräsbeck syndrome;   

Others  :  1122597
DOI  :  10.1186/1471-2350-14-111

 received in 2012-07-16, accepted in 2013-10-18,  发布年份 2013

【 摘 要 】

Background

Imerslund-Gräsbeck Syndrome (IGS) is a rare genetic disorder characterised by juvenile megaloblastic anaemia. IGS is caused by mutations in either of the genes encoding the intestinal intrinsic factor-vitamin B₁₂ receptor complex, cubam. The cubam receptor proteins cubilin and amnionless are both expressed in the small intestine as well as the proximal tubules of the kidney and exhibit an interdependent relationship for post-translational processing and trafficking. In the proximal tubules cubilin is involved in the reabsorption of several filtered plasma proteins including vitamin carriers and lipoproteins. Consistent with this, low-molecular-weight proteinuria has been observed in most patients with IGS. The aim of this study was to characterise novel disease-causing mutations and correlate novel and previously reported mutations with the presence of low-molecular-weight proteinuria.

Methods

Genetic screening was performed by direct sequencing of the CUBN and AMN genes and novel identified mutations were characterised by in silico and/or in vitro investigations. Urinary protein excretion was analysed by immunoblotting and high-resolution gel electrophoresis of collected urines from patients and healthy controls to determine renal phenotype.

Results

Genetic characterisation of nine IGS patients identified two novel AMN frameshift mutations alongside a frequently reported AMN splice site mutation and two CUBN missense mutations; one novel and one previously reported in Finnish patients. The novel AMN mutations were predicted to result in functionally null AMN alleles with no cell-surface expression of cubilin. Also, the novel CUBN missense mutation was predicted to affect structural integrity of the IF-B₁₂ binding site of cubilin and hereby most likely cubilin cell-surface expression. Analysis of urinary protein excretion in the patients and 20 healthy controls revealed increased urinary excretion of cubilin ligands including apolipoprotein A-I, transferrin, vitamin D-binding protein, and albumin. This was, however, only observed in patients where plasma membrane expression of cubilin was predicted to be perturbed.

Conclusions

In the present study, mutational characterisation of nine IGS patients coupled with analyses of urinary protein excretion provide additional evidence for a correlation between mutation type and presence of the characteristic low-molecular-weight proteinuria.

【 授权许可】

   
2013 Storm et al.; licensee BioMed Central Ltd.

【 图 表 】

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