A new type of congenital disorders of glycosylation (CDG-Ii) provides new insights into the early steps of dolichol-linked oligosaccharide biosynthesis

J Biol Chem. 2003 Jun 20;278(25):22498-505. doi: 10.1074/jbc.M302850200. Epub 2003 Apr 8.


Deficiency of GDP-Man:Man1GlcNAc2-PP-dolichol mannosyltransferase (hALG2), is the cause of a new type of congenital disorders of glycosylation (CDG) designated CDG-Ii. The patient presented normal at birth but developed in the 1st year of life a multisystemic disorder with mental retardation, seizures, coloboma of the iris, hypomyelination, hepatomegaly, and coagulation abnormalities. An accumulation of Man1GlcNAc2-PP-dolichol and Man2GlcNAc2-PP-dolichol was observed in skin fibroblasts of the patient. Incubation of patient fibroblast extracts with Man1GlcNAc2-PP-dolichol and GDP-mannose revealed a severely reduced activity of the mannosyltransferase elongating Man1GlcNAc2-PP dolichol. Because the Saccharomyces cerevisiae mutant alg2-1 was known to accumulate the same shortened dolichol-linked oligosaccharides as the patient, the yeast ALG2 sequence was used to identify the human ortholog. Genetic analysis revealed that the patient was heterozygous for a single nucleotide deletion and a single nucleotide substitution in the human ortholog of yeast ALG2. Expression of wild type but not of mutant hALG2 cDNA restored the mannosyltransferase activity and the biosynthesis of dolichol-linked oligosaccharides both in patient fibroblasts and in the alg2-1 yeast cells. hALG2 was shown to act as an alpha1,3-mannosyltransferase. The resulting Manalpha1,3-ManGlcNAc2-PP dolichol is further elongated by a yet unknown alpha1,6-mannosyltransferase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Carbohydrate Metabolism, Inborn Errors / genetics*
  • Carbohydrate Sequence
  • Cell Line
  • DNA Primers
  • Dolichol Phosphates / metabolism
  • Dolichols / metabolism*
  • Female
  • Fibroblasts
  • Genetic Complementation Test
  • Glycosylation
  • Humans
  • Male
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Oligosaccharides / biosynthesis*
  • Pedigree
  • Polyisoprenyl Phosphate Monosaccharides / metabolism
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / metabolism*
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization


  • DNA Primers
  • Dolichol Phosphates
  • Dolichols
  • Oligosaccharides
  • Polyisoprenyl Phosphate Monosaccharides
  • dolichol pyrophosphate
  • N-acetylglucosaminylpyrophosphoryldolichol