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Clinical and molecular features of three patients with congenital disorders of glycosylation type Ih (CDG-Ih) (ALG8 deficiency)
  1. E Schollen1,
  2. C G Frank2,
  3. L Keldermans1,
  4. R Reyntjens1,
  5. C E Grubenmann3,
  6. P T Clayton4,
  7. B G Winchester4,
  8. J Smeitink5,
  9. R A Wevers6,
  10. M Aebi2,
  11. T Hennet3,
  12. G Matthijs1
  1. 1Center for Human Genetics, University of Leuven, Leuven, Belgium
  2. 2Institute of Microbiology, Swiss Federal Institute of Technology, Zürich, Switzerland
  3. 3Institute of Physiology, University of Zürich, Zürich, Switzerland
  4. 4Great Ormond Street Hospital for Children and Institute of Child Health, University College London, London, UK
  5. 5Department of Paediatrics, University Medical Center Nijmegen, Nijmegen, The Netherlands
  6. 6Laboratory of Paediatrics and Neurology, University Medical Center Nijmegen, Nijmegen, The Netherlands
  1. Correspondence to:
 G Matthijs
 Center for Human Genetics, University of Leuven, Herestraat 49, B-3000 Leuven, Belgium;

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Protein glycosylation is an essential post-translational modification of various proteins, affecting their folding, sorting, and function. Inborn defects in the assembly and processing of glycans on glycoproteins are known as congenital disorders of glycosylation (CDG) and can affect both N- and O-glycosylation (for reviews see Marquardt and Denecke,1 Jaeken,2 and Grunewald et al3). N-glycosylation defects and especially defects in the assembly of the dolichol linked N-glycan precursor in the endoplasmic reticulum (ER) (CDG-I) result in hypoglycosylation of many kinds of (serum) glycoproteins. CDG-I is therefore a group of multisystemic disorders.

The assembly of the N-glycan precursor in the ER is a highly ordered process involving at least 30 known gene products. Mutations in 11 of these (PMM2, MPI, ALG6, DPM1, ALG3, MPDU1, ALG12, ALG8, ALG2, DPAGT1, and ALG1) have been shown to cause CDG type I (CDG-Ia to CDG-Ik).2,4–10 Although it remains difficult to define a characteristic clinical phenotype for each type of CDG, mainly because only a limited number of patients have been assigned to most types, they generally share hypotonia and different degrees of mental retardation. Central nervous system defects are absent in CDG-Ib patients (with a deficiency of phosphomannose isomerase, MPI) and in the recently published CDG-Ih patient (with a deficiency of dolichyl-P-Glc: Glc1Man9GlcNAc2-PP-dolichyl α1, 3-glucosyltransferase, ALG8).4 CDG-Ib patients present mainly with hypoglycaemia, coagulopathy, hepatomegaly, protein-losing enteropathy, hepatic fibrosis, cyclic vomiting, and diarrhoea.11–14 It is the only type with an efficient therapy because dietary mannose can be used via an alternative pathway to generate mannose-6-phosphate that is normally produced from fructose-6-phosphate by the action of MPI.

The only CDG-Ih patient described so far shares this relatively mild presentation with severe diarrhoea and moderate hepatomegaly.4

Our cohort of unsolved CDG patients included …

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  • This work was supported by TANDEM grant 3238–056350.99 from the Swiss National Foundation and by grant G.0243.98 from the Foundation for Scientific Research (FWO, Flanders). Collaboration occurred in the context of EUROGLYCAN, a network for CDG research funded by the Fifth Framework Program of the European Commission (QLG1-CT-2000-00047).

  • Conflict of interest: none declared.