Galactose Supplementation in Patients With TMEM165-CDG Rescues the Glycosylation Defects.
BACKGROUND
TMEM165 deficiency is a severe multisystem disease that manifests with metabolic, endocrine, and skeletal involvement. It leads to one type of congenital disorders of glycosylation (CDG), a rapidly growing group of inherited diseases in which the glycosylation process is altered. Patients have decreased galactosylation by serum glycan analysis. There are >100 CDGs, but only specific types are treatable.


OBJECTIVE
Galactose has been shown to be beneficial in other CDG types with abnormal galactosylation. The aim of this study was to characterize the effects of galactose supplementation on Golgi glycosylation in TMEM165-depleted HEK293 cells, as well as in 2 patients with TMEM165-CDG and in their cultured skin fibroblast cells.


METHODS
Glycosylation was assessed by mass spectrometry, western blot analysis, and transferrin isoelectrofocusing.


METHODS
Both unrelated patients with TMEM165-CDG with the same deep intronic homozygous mutation (c.792+182G>A) were allocated to receive d-galactose in a daily dose of 1 g/kg.


RESULTS
We analyzed N-linked glycans and glycolipids in knockout TMEM165 HEK293 cells, revealing severe hypogalactosylation and GalNAc transfer defects. Although these defects were completely corrected by the addition of Mn2+, we demonstrated that the observed N-glycosylation defect could also be overcome by galactose supplementation. We then demonstrated that oral galactose supplementation in patients with TMEM165-deficient CDG improved biochemical and clinical parameters, including a substantial increase in the negatively charged transferrin isoforms, and a decrease in hypogalactosylated total N-glycan structures, endocrine function, and coagulation parameters.


CONCLUSIONS
To our knowledge, this is the first description of abnormal glycosylation of lipids in the TMEM165 defect and the first report of successful dietary treatment in TMEM165 deficiency. We recommend the use of oral d-galactose therapy in TMEM165-CDG.
Université Lille, Centre National de la Recherche Française, UMR 8576-Unité de Glycobiologie Structurale et Fonctionnelle-Unité de Glycobiologie Structurale et Fonctionnelle, F-59000 Lille, France.
Willy
W
Morelle
Université Lille, Centre National de la Recherche Française, UMR 8576-Unité de Glycobiologie Structurale et Fonctionnelle-Unité de Glycobiologie Structurale et Fonctionnelle, F-59000 Lille, France.
Sven
S
Potelle
Metabolic Center, Department of Pediatrics, University Hospitals Leuven, Leuven B-3000, Belgium.
Peter
P
Witters
Hayward Genetics Center, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Sunnie
S
Wong
Department of Physiology and Biophysics, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205.
Leslie
L
Climer
Department of Physiology and Biophysics, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205.
Vladimir
V
Lupashin
Center for Human Genetics, KU Leuven, Leuven B-3000, Belgium.
Gert
G
Matthijs
Hayward Genetics Center, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Therese
T
Gadomski
Metabolic Center, Department of Pediatrics, University Hospitals Leuven, Leuven B-3000, Belgium.
Jaak
J
Jaeken
Metabolic Center, Department of Pediatrics, University Hospitals Leuven, Leuven B-3000, Belgium.
David
D
Cassiman
Metabolic Center, Department of Pediatrics, University Hospitals Leuven, Leuven B-3000, Belgium.|Hayward Genetics Center, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Eva
E
Morava
Université Lille, Centre National de la Recherche Française, UMR 8576-Unité de Glycobiologie Structurale et Fonctionnelle-Unité de Glycobiologie Structurale et Fonctionnelle, F-59000 Lille, France.
François
F
Foulquier
D000328:Adult; D017920:Antiporters; D027682:Cation Transport Proteins; D002648:Child; D018981:Congenital Disorders of Glycosylation / Q000178:diet therapy* / Q000235:genetics* / Q000473:pathology; D019587:Dietary Supplements; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D005690:Galactose / Q000494:pharmacology* / Q000627:therapeutic use*; D006031:Glycosylation / Q000187:drug effects*; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics*; D009154:Mutation; D016896:Treatment Outcome
D017920:Antiporters; D027682:Cation Transport Proteins; D008565:Membrane Proteins; C575014:TMEM165 protein, human; D005690:Galactose