The function of PIGQ (phosphatidylinositol glycan anchor biosynthesis class Q, Ensembl gene identifier ENSG00000007541) is as follows. 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. {ECO:0000269|PubMed:16162815, ECO:0000269|PubMed:9463366}.