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.

The two best known blood group systems are ABO and Rh but blood is more complex and matching across the other groups can be lifesaving.

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. 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.

The most common reason for being AnWj-negative is due to suffering from a haematological disorder or some types of cancer which suppress antigen expression.

Read the full University of Bristol news item

'Deletions in the MAL gene result in loss of Mal protein, defining the rare inherited AnWj-negative blood group phenotype' by Louise A Tilley, Ashley Mark Toye, Timothy J Satchwell, Nicole M Thornton et al. in Blood