Tn syndrome is a rare autoimmune disease characterized by the expression of the Tn antigen, an incompletely glycosylated membrane glycoprotein, on all blood cell lineages. The epitope of the Tn antigen is terminal alpha-N-acetylgalactosamine alpha-linked to either a serine or threonine amino-acid residue. The defect may be due to a malfunction of the glycosylating enzyme T-synthase. Tn syndrome is associated with a somatic mutation in Cosmc gene, encoding a molecular chaperone that is required for the proper folding and hence full activity of T-synthase.
