Members of this family comprise various XK-related proteins, that are involved in sodium-dependent transport of neutral amino acids or oligopeptides. These proteins are responsible for the Kx blood group system - defects results in McLeod syndrome [MIM:314850], an X-linked multi-system disorder characterised by late onset abnormalities in the neuromuscular and hematopoietic systems [1][2].

1: Isolation of the gene for McLeod syndrome that encodes a novel membrane transport protein. Ho M, Chelly J, Carter N, Danek A, Crocker P, Monaco AP; Cell. 1994;77:869-880. PMID:8004674

2: Purification and partial characterization of the erythrocyte Kx protein deficient in McLeod patients. Khamlichi S, Bailly P, Blanchard D, Goossens D, Cartron JP, Bertrand O; Eur J Biochem. 1995;228:931-934. PMID:7737196