Part of the glycosylphosphatidylinositol-N-acetylglucosaminyltransferase (GPI-GnT) complex that catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol and participates in the first step of GPI biosynthesis (PubMed:16162815). May act by regulating the catalytic subunit PIGA (PubMed:16162815). Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. Component of the glycosylphosphatidylinositol-N-acetylglucosaminyltransferase (GPI-GnT) complex composed at least by PIGA, PIGC, PIGH, PIGP, PIGQ, PIGY and DPM2 (PubMed:16162815). Interacts directly with PIGA; this interaction regulates glycosylphosphatidylinositol-N-acetylglucosaminyltransferase activity (PubMed:16162815). Does not interact with Ras proteins (PubMed:16162815). The disease is caused by variants affecting the gene represented in this entry. PREY and PIGY, 2 apparently unrelated proteins, are respectively the product of an upstream and a downstream ORF contained in a single bicistronic transcript.