X-linked Kx blood group antigen, Kell and VPS13A binding protein (XK)

The X-linked Kx blood group antigen, Kell and VPS13A binding protein (XK) is a multi-pass membrane transport protein encoded by the XK gene on the X chromosome[1][3][5][7]. XK is found on red blood cells and multiple other tissues, most notably the brain, heart, and muscle[1]. On red blood cells, it carries the Kx antigen, crucial for blood group typing and transfusion compatibility, and forms a complex with the Kell glycoprotein via a disulfide bond[3][4]. Its transporter function is not fully defined, but it also recruits VPS13A lipid transfer protein to the endoplasmic reticulum in other cell types[5]. Mutations or deletions in XK lead to McLeod syndrome—an X-linked disorder causing neurodegeneration, myopathy, hemolytic anemia, and cardiomyopathy, with high risk of transfusion reactions due to loss of Kx and Kell antigens on red blood cells[6][8]. Diagnosis relies on genetic analysis and serological typing, with clinical management focused on transfusion safety and supportive care[4][6][8].

Other names

XKXKR1XRG1Kx antigenKxX1kKell complex 37 kDa componentMembrane transport protein XKEndoplasmic reticulum membrane adapter protein XKKell blood group precursor (McLeod phenotype)Kell blood group complex subunit (McLeod syndrome)Kell and VPS13A binding proteinKell blood group precursorNACNA

No direct drug mechanism; therapeutic challenges center on preventing immune reactions (acute hemolytic transfusion reaction) from anti-Kx alloantibodies in patients lacking Kx antigen due to XK mutations. Prevention focuses on antigen matching during transfusion in McLeod phenotype.