Functional and electrophysiological characterization of four non-truncating mutations responsible for creatine transporter (SLC6A8) deficiency syndrome.
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 [(14)C]-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.
INSERM U781 and Paris-Descartes University, Necker-Enfants Malades Hospital, 149 rue de Sèvres, 75743 Paris cedex 15, France.
Vassili
V
Valayannopoulos
Naziha
N
Bakouh
Michel
M
Mazzuca
Luc
L
Nonnenmacher
Laurence
L
Hubert
Fatna-Léa
FL
Makaci
Allel
A
Chabli
Gajja S
GS
Salomons
Caroline
C
Mellot-Draznieks
Emilie
E
Brulé
Pascale
P
de Lonlay
Hervé
H
Toulhoat
Arnold
A
Munnich
Gabrielle
G
Planelles
Yves
Y
de Keyzer
D000818:Animals; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D003401:Creatine / Q000235:genetics / Q000378:metabolism; D055724:Electrophysiological Phenomena; D005347:Fibroblasts / Q000378:metabolism; D005838:Genotype; D006801:Humans; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000172:deficiency* / Q000235:genetics* / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D050480:Plasma Membrane Neurotransmitter Transport Proteins / Q000172:deficiency* / Q000235:genetics* / Q000378:metabolism; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism
D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D050480:Plasma Membrane Neurotransmitter Transport Proteins; C094770:SLC6A8 protein, human; C080679:creatine transporter; D003401:Creatine