• Researchers from NHS Blood and Transplant (Bristol), NHSBT’s International Blood Group Reference Laboratory (IBGRL) and the University of Bristol have discovered a new blood group named MAL.

• They identified the genetic background of the previously known but mysterious AnWj blood group antigen, thus allowing identification and treatment of rare patients lacking this blood group.

• The AnWj antigen — an antigen is a surface marker — was discovered in 1972 but its genetic background was unknown until now.

• 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.

• The new blood group system (MAL) is the 47th ever to be discovered.

What is the AnWj antigen?

• 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. This research allows the development of new genotyping tests for detecting such rare individuals and reducing the risk of transfusion-associated complications.

• The research team established that AnWj is carried on the Mal protein. More than 99.9 per cent 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.

• Only a very small number of people are AnWj-negative due to a genetic cause. There were five genetically AnWj-negative individuals in the study including a family of Arab-Israelis. 

• The blood tested included a sample given by a lady in 2015 who was the first AnWj-negative person to be discovered in the 1970s.

• The research team used whole exome sequencing — the genetic sequencing of all DNA that encodes proteins — to show that these rare inherited cases were caused by homozygous DNA sequence deletions in the MAL gene, which codes for Mal protein.

Blood group system

• The circulatory system consists of the heart, blood vessels and blood. The blood carries oxygen and nutrients to every cell in the body and picks up waste products (such as carbon dioxide) for removal from the body.

• The bulk of your blood is made up of plasma. Floating in the plasma are the red blood cells that carry oxygen, the white cells that form part of the immune system, and clotting cells called platelets.

• The blood group is identified by antibodies and antigens. Antibodies are proteins found in plasma. They are part of the body’s natural defences. They recognise foreign substances, such as germs, and alert the immune system. Antigens are protein molecules found on the surface of red blood cells.

• The two main ways to classify blood groups are the ABO system and the Rh system. Together, they make up the eight main blood groups.

• Red blood cells sometimes have another antigen, a protein known as the RhD antigen. If this is present, the blood group is RhD positive. If it is absent, the blood group is RhD negative.

• Other blood group systems exist. Researchers have identified minor blood groups with new antigens still being discovered.

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