Ethanolamine phosphate transferase involved in glycosylphosphatidylinositol-anchor biosynthesis. Transfers ethanolamine phosphate to the GPI third mannose which links the GPI-anchor to the C-terminus of the proteins by an amide bond. Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. Forms a complex with PIGF. PIGF is required to stabilize PIGO (By similarity). Additional isoforms seem to exist. The disease is caused by variants affecting the gene represented in this entry. Belongs to the PIGG/PIGN/PIGO family. PIGO subfamily. Truncated N-terminus. Truncated N-terminus.