Polypeptide-N-Acetylgalactosaminyltransferase 5 (GALNT5)

Hereditary multiple exostoses (HME) is an autosomal dominant condition in which bony outgrowths occur from the juxtaepiphyseal regions of the long bones. In a few percent of cases these exostoses undergo malignant transformation to chondrosarcomas.

One recent study has also reported that these proteins co-purify with glycosyltransferase (GlcA and GlcNAc transferase) activity and on that basis it has been postulated that they are themselves glycosyl-transferases. Significantly, both these interactions were abrogated by a disease-causing EXT mutation, indicating that they are important in the etiology of HME. The EXT2-GalNAc-T5 interaction provides the first direct physical link between EXT proteins and known components of glycosamino-glycan synthesis.