On Sept. 16, 2024, researchers from the National Health Service Blood and Transplant (Bristol), NHSBT’s International Blood Group Reference Laboratory (IBGRL) and the University of Bristol identified the genetic background of the previously known but mysterious AnWj blood group antigen.

The findings allow identification and treatment of rare patients lacking this blood group. Some people can lack this blood group due to the effect of illness, but the rare inherited form of the AnWj-negative phenotype has only been found in a handful of individuals – though due to this discovery it will now be easier to find others in the future.

If people who are AnWj-negative receive AnWj-positive blood they could have a transfusion reaction, and this research allows development of new genotyping tests for detecting such rare individuals and reducing the risk of transfusion-associated complications.

The AnWj antigen – an antigen is a surface marker – was discovered in 1972 but its genetic background was unknown until now.(3) The new research, to be published by Blood, the journal of the American Society of Hematology, and now available online in pre-print, establishes a new blood group system (MAL), the 47^th ever to be discovered, as home to the AnWj antigen.

The research team established that AnWj is carried on the Mal protein. More than 99.9% of people are AnWj-positive, and such individuals were shown to express full-length Mal protein on their red cells, which was not present on the cells of AnWj-negative individuals. The team identified homozygous deletions in the MAL gene associated with the inherited AnWj-negative phenotype.