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01-01-2013 | Original Article

Functional and electrophysiological characterization of four non-truncating mutations responsible for creatine transporter (SLC6A8) deficiency syndrome

Authors: Vassili Valayannopoulos, Naziha Bakouh, Michel Mazzuca, Luc Nonnenmacher, Laurence Hubert, Fatna-Léa Makaci, Allel Chabli, Gajja S. Salomons, Caroline Mellot-Draznieks, Emilie Brulé, Pascale de Lonlay, Hervé Toulhoat, Arnold Munnich, Gabrielle Planelles, Yves de Keyzer

Published in: Journal of Inherited Metabolic Disease | Issue 1/2013

Abstract

Intellectual disability coupled with epilepsy are clinical hallmarks of the creatine (Cr) transporter deficiency syndrome resulting from mutations in the SLC6A8 gene. So far characterization of pathogenic mutations of SLC6A8 has been limited to Cr uptake. The aim of our study was to characterize the electrogenic and pharmacological properties of non truncating SLC6A8 mutations identified in patients presenting variable clinical severity. Electrophysiological and pharmacological properties of four mutants (including two novel ones) were studied in X. laevis oocyte expression system. Creatine uptake was assessed with [¹⁴C]-Cr in X. laevis and patients’ fibroblasts. Subcellular localization was determined by immunofluorescence and western blot. All mutants were properly targeted to the plasma membrane in both systems. Mutations led to the complete loss of both electrogenic and transport activities in X. laevis and Cr uptake in patients’ fibroblasts. Among the Cr analogs tested, guanidinopropionate induced an electrogenic activity with the normal SLC6A8 transporter similar to creatine whereas a phosphocreatine derivative, PCr-Mg-CPLX, resulted in partial activity. SLC6A8 mutants displayed no electrogenic activity with all Cr analogs tested in X. laevis oocytes. Although the mutations altered various domains of SLC6A8 Cr uptake and electrogenic properties were completely inhibited and could not be dissociated. Besides the metabolic functions of Cr, the loss of SLC6A8 electrogenic activity, demonstrated here for the first time, may also play a role in the altered brain functions of the patients.

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Title: Functional and electrophysiological characterization of four non-truncating mutations responsible for creatine transporter (SLC6A8) deficiency syndrome
Authors: Vassili Valayannopoulos
Naziha Bakouh
Michel Mazzuca
Luc Nonnenmacher
Laurence Hubert
Fatna-Léa Makaci
Allel Chabli
Gajja S. Salomons
Caroline Mellot-Draznieks
Emilie Brulé
Pascale de Lonlay
Hervé Toulhoat
Arnold Munnich
Gabrielle Planelles
Yves de Keyzer
Publication date: 01-01-2013
Publisher: Springer Netherlands
Published in: Journal of Inherited Metabolic Disease / Issue 1/2013
Print ISSN: 0141-8955
Electronic ISSN: 1573-2665
DOI: https://doi.org/10.1007/s10545-012-9495-9

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