This gene encodes a protein with both O-glucosyltransferase and O-xylosyltransferase activity which localizes to the lumen of the endoplasmic reticulum. This protein has a carboxy-terminal KTEL motif which is predicted to function as an endoplasmic reticulum retention signal. This gene is an essential regulator of Notch signalling and likely plays a role in cell fate and tissue formation during development. It may also play a role in the pathogenesis of leukemia. Mutations in this gene have been associated with the autosomal dominant genodermatosis Dowling-Degos disease 4. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Apr 2014].