The EMM blood group system consists of one antigen, Emm, carried on the glycosylphosphatidylinositol (GPI) anchor to which all GPI-linked proteins are attached. The Emm antigen is thought to involve the ethanolamine phosphate (EtNP) on the second mannose (Man2) of the GPI-anchor. This EtNP is specifically added to Man2 by GPI-ethanolaminetransferase II enzymatic complex GPI-ETII, which is composed of two proteins PIGF and PIGG. The catalytic part of GPI-ETII is defined by PIGG, encoded by the PIGG gene. The presence or absence of the Emm antigen is defined by the activity of the PIGG gene, with loss of function variants leading to the Emm– phenotype.