An antigen without a gene
The AnWj antigen was identified in 1972 and named after two patients, Anton and Wj, whose blood contained the antibody. For more than 50 years no one could say which gene produced it, which made it impossible to test donors properly for the rare people who lack it. Now researchers at NHS Blood and Transplant's International Blood Group Reference Laboratory in Bristol, working with the University of Bristol and international partners, have found the answer on the MAL gene.
MAL becomes the 47th blood group system
Because a blood group system requires an antigen with a defined genetic and molecular basis, the finding created one: MAL, registered as ISBT 047 by the International Society of Blood Transfusion. It was one of four systems ratified in the society's 2026 terminology report, alongside ER, CD36 and ATP11C. There are now 47 blood group systems and more than 360 known antigens. People with ordinary AnWj-positive blood carry the full-length Mal protein on their red cells; AnWj-negative people do not. The Mal protein helps stabilise cell membranes and move molecules across them.
Why rare negatives matter
Red cells that lack the antigen are rare, but a transfusion of AnWj-positive blood into a patient who carries the antibody can cause a reaction. In one 2026 case, a 75-year-old man with severe anaemia and an anti-AnWj autoantibody needed blood when no compatible units were available; doctors weighed the risk and transfused unmatched red cells, and he did not develop a haemolytic reaction. In another case, a patient with high-grade B-cell lymphoma received sutimlimab, a drug that blocks part of the complement pathway, after incompatible transfusions were followed by signs of red cell destruction; laboratory markers improved, though the authors cautioned against firm conclusions from one complicated case.
What changes for patients
The practical result is a test. Reference laboratories can now screen donors genetically for MAL variants instead of relying on scarce antisera and case-by-case detective work, which shortens the search for compatible units for patients who need repeated transfusions. The genetic background of AnWj has been a mystery for more than 50 years, said Louise Tilley of NHS Blood and Transplant, who worked on the puzzle for nearly two decades of her career.