folder

Unusual clinical presentation and possible rescue of a novel Claudin-16 mutation

Authors

  • D. Mueller
  • P.J. Kausalya
  • D. Bockenhauer
  • J. Tumfart
  • I.C. Meij
  • M.J. Dillon
  • W. van't Hoff
  • W. Hunziker

Journal

  • Journal of Clinical Endocrinology and Metabolism

Citation

  • J Clin Endocrinol Metab 91 (8): 3076-3079

Abstract

  • CONTEXT: Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is caused by a dysfunction of Claudin-16 (CLDN16) and characterized by renal wasting of Mg(2+) and Ca(2+). The precise molecular defects remain unclear. OBJECTIVE: To study the clinical parameters in suspected FHHNC patients, identify mutations in the CLDN16 gene and analyze molecular defects associated with the mutant protein. DESIGN, SETTING, PARTICIPANTS: Sequencing of the CLDN16 gene from two siblings diagnosed with FHHNC. Expression and characterization of the mutant protein in renal MDCK cells. OUTCOME MEASURES: Standard urine and serum parameters to diagnose FHHNC were determined. Mutations in the CLDN16 gene were identified. The subcellular distribution of the mutant protein was analyzed by immunofluorescence microscopy. RESULTS: Urine and blood analysis showed signs typical for FHHNC. One patient, in addition, presented with hypocalcemic tetany, a phenomenon so far not described for FHHNC. Both siblings carry a novel mutation in CLDN16, Y207X. The review of medical records showed that hypocalcaemia is not uncommon in the early childhood of FHHNC patients. Expressed in MDCK cells, the Y207X mutant is not detected at tight junctions but instead found in lysosomes and, to a lesser extent, the endoplasmic reticulum. Surface expression can be rescued by inhibiting clathrin-mediated internalization. CONCLUSIONS: We propose that mutations in CLDN16 are considered in childhood hypocalcaemia. CLDN16 Y207X is transiently delivered to the plasma membrane but not retained and rapidly retrieved by internalization. Inhibitors of endocytosis may provide novel therapeutic strategies.


DOI

doi:10.1210/jc.2006-0200