This gene encodes an endoplasmic reticulum membrane protein that is required for utilization of the mannose donor mannose-P-dolichol in the synthesis of lipid-linked oligosaccharides and glycosylphosphatidylinositols. Mutations in this gene result in congenital disorder of glycosylation type If. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Dec 2008].