This gene encodes a mannosyltransferase enzyme involved inThe biosynthesis of glycosylphosphatidylinositol (GPI). GPI is a complex glycolipid that functions as a membrane anchor for many proteins and plays a role in multiple cellular processes including protein sorting and signal transduction.The encoded protein is localized toThe endoplasmic reticulum and transfersThe second mannose toThe GPI backbone. Mutations inThis gene are associated with hyperphosphatasia mental retardation syndrome. Alternatively spliced transcript variants have been observed forThis gene. [provided by RefSeq, Feb 2011]