In 2024, British scientists announced the discovery of a new blood group system. It is associated with the Mal protein, necessary for the production of a blood cell antigen called AnWj. Over 99.9 percent of people have AnWj-positive blood, and less than 1 percent are AnWj-negative.

'Therefore, the clinical significance of this discovery is not great, although it has been found that rare haemolytic complications may result from incompatibility concerning this particular antigen', says Professor Wiesław Jędrzejczak from the Department of Hematology, Transplantation and Internal Medicine at the Medical University of Warsaw, a specialist in haematology, internal medicine, clinical oncology and transplantology.

The first reports of atypical red blood cells (erythrocytes) that do not have the AnWj molecule on their surface date back to the 1970s. Such blood cells were found in samples taken from a pregnant woman. Decades of research have revealed that the AnWj antigen occurs in over 99.9% of people, and in the small percentage who do not have it, it is due to unusual blood disorders or a rare mutation.

However, only now, after 50 years of research, scientists from NHS Blood and Transplant (NHSBT) and the University of Bristol have shown that the AnWj antigen is associated with the Mal protein, encoded by the MAL gene.

In people with the hereditary AnWj-negative blood group, there is a deletion of the MAL gene (i.e. removal of its fragment), which - as it turns out - is necessary for the formation of the AnWj antigen in the erythrocyte membrane.

However, the situation of someone's blood being AnWj-negative is extremely rare. For it to happen, the person must inherit two mutated alleles of the MAL gene from their parents or lose this antigen as a result of rare haemolytic complications.

'In haematology, there are situations where a given person, e.g. after many blood transfusions, begins to develop resistance to subsequent transfusions at some point. When looking for the cause, we check the compatibility in terms of the ABO blood group system, the Rh system, and then the lesser-known systems, of which there are over forty. In very rare cases, it may turn out that this incompatibility will concern the antigen described by the authors of this publication, associated with the MAL gene mutation', Jędrzejczak explains.

According to the expert, this is therefore another discovery in the field of haematology, the clinical significance of which may not be great, but one that certainly broadens our knowledge about the functioning of the human body.

Professor Wiesław Jędrzejczak reminds that - contrary to common knowledge - the ABO blood group system and the system based on the Rh antigen, which doctors use most often, are not the only ones. There are 44 other known blood group antigen systems, and their common feature is that they are based on the presence or absence of specific molecules (antigens) on the surface of red blood cells.

All medical procedures requiring the administration of foreign blood to a patient are preceded by a serological compatibility test, i.e. determining the blood type of the donor and recipient and conducting a cross-match. The aim of these procedures is to avoid a dangerous reaction of the patient's immune system to foreign erythrocyte antigens, which could lead to complications or rejection of the transfused blood.

JHowever, even with these compatibility tests, in very rare cases there are situations in which the recipient's body rejects the blood despite the fact that all tests indicate its compatibility. One possible cause of such situations is the incompatibility of patients due to the presence of other antigens, including AnWj. Discovering further blood antigens may therefore improve the safety of transfusion and increase the effectiveness of treatment in people with rare haemolytic disorders.

Katarzyna Czechowicz (PAP)

PAP - Science in Poland

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