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. Belongs to the PIGG/PIGN/PIGO family. PIGO subfamily. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.