Protein glycosylation: chaperone mutation in Tn syndrome

Nature. 2005 Oct 27;437(7063):1252. doi: 10.1038/4371252a.


Tn syndrome is a rare autoimmune disease in which subpopulations of blood cells in all lineages carry an incompletely glycosylated membrane glycoprotein, known as the Tn antigen. This truncated antigen has the sugar N-acetylgalactosamine alpha-linked to either a serine or threonine amino-acid residue, whereas the correct T antigen has an additional terminal galactose; the defect may be due to a malfunction of the glycosylating enzyme T-synthase. Here we show that Tn syndrome is associated with a somatic mutation in Cosmc, a gene on the X chromosome that encodes a molecular 'chaperone' that is required for the proper folding and hence full activity of T-synthase. The production of the autoimmune Tn antigen by a glycosyltransferase enzyme rendered defective by a disabled chaperone may have implications for other Tn-related disorders such as IgA nephropathy, a condition that can result in renal failure.

MeSH terms

  • Alleles
  • Antigens, Tumor-Associated, Carbohydrate / chemistry
  • Antigens, Tumor-Associated, Carbohydrate / metabolism*
  • Autoimmune Diseases / genetics*
  • Autoimmune Diseases / metabolism*
  • Female
  • Galactosyltransferases / chemistry
  • Galactosyltransferases / metabolism*
  • Genetic Diseases, X-Linked / genetics
  • Glycosylation
  • Humans
  • Male
  • Molecular Chaperones / genetics*
  • Molecular Chaperones / metabolism
  • Mutation / genetics*
  • Syndrome


  • Antigens, Tumor-Associated, Carbohydrate
  • C1GALT1C1 protein, human
  • Molecular Chaperones
  • Tn antigen
  • C1GALT1 protein, human
  • Galactosyltransferases