The Yt blood group system consists of 5 antigens carried on a membrane bound GPI-linked glycoprotein acetylcholinesterase (AChE) that consists of 617 amino acids. It has a leader sequence of 31 amino acids and a carboxyl-terminal GPI motif of 29 amino acids, both of which are cleaved from the mature erythrocyte isoform AChE-E. The protein is encoded by ACHE (or YT, acceptable if analysis is to predict a blood group antigen).