The discovery of a new blood group system known as MAL by NHS Blood and Transplant scientists, in collaboration with the University of Bristol, has marked the culmination of a 50-year quest to unveil the mystery surrounding the AnWj antigen.
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Blood groups play a critical role in medicine, particularly in blood transfusions. The well-known blood group systems are ABO and Rh, but there are numerous other systems that are vital to consider.
Within each blood group, red blood cells carry surface markers known as antigens. For instance, the ABO system has A and B antigens with individuals having either one, both or neither of these antigens on their red cells.
Rh blood group is characterized by the presence or absence of the RhD antigen. Currently, there are 47 recognized blood group systems collectively containing more than 360 antigens. Each system has a unique set of antigens that can determine compatibility during transfusions.
MAL has now been added to this list, the 47th blood group system. The discovery was led by researchers from the NHS Blood and Transplant and the University of Bristol.
The importance of this new system lies in its association with the AnWj antigen, a marker present in over 99.9% of the global population.
However, the AnWj-negative phenotype is extremely rare and can have implications for blood transfusions. The research was a culmination of efforts spanning over 50 years, where scientists finally identified the genetic basis of the AnWj antigen.
AnWj was discovered in 1972, but its genetic background remained unknown until now. The absence of this antigen can lead to transfusion reactions especially if AnWj-negative individuals receive AnWj-positive blood.
A team of researchers led by Dr. Louise Tilley of NHS Blood and Transplant had been working on this puzzle for almost two decades.
After extensive research, they established that the AnWj antigen is carried on the Mal protein, a discovery that has huge implications for identifying and treating patients with the rare AnWj-negative phenotype.
The researchers discovered that 99.9% of the population expresses the full-length Mal protein on their red blood cells, which carries the AnWj antigen.
Individuals with the AnWj-negative phenotype lack this antigen due to a homozygous deletion in the MAL gene, which encodes the Mal protein.
The absence of this protein in AnWj-negative individuals makes them susceptible to complications if they receive AnWj-positive blood. This genetic cause is rare and only a handful of individuals including an Arab-Israeli family have been identified with the inherited form of the AnWj-negative phenotype.
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The discovery was made by a team of researchers at NHSBT’s International Blood Group Reference Laboratory (IBGRL) in Filton, South Gloucestershire in collaboration with the University of Bristol. Led by senior scientists like Louise Tilley and Nicole Thornton, the team finally identified the genetic basis of the AnWj antigen and revealed it as part of MAL.
The research team developed a world-first genotyping test that can now identify patients who are AnWj-negative. This discovery is set to improve care for rare patients, who may have previously been at risk of dangerous transfusion reactions.
The research revealed that the AnWj antigen is carried on the Mal protein with over 99.9% of the population being AnWj-positive, meaning they express the full-length Mal protein on their red blood cells.
A small fraction of individuals are genetically AnWj-negative, due to homozygous deletions in the MAL gene. This deletion prevents the expression of the Mal protein on red cells, which can lead to complications in transfusions.
While the inherited form of the AnWj-negative phenotype is extremely rare, the antigen suppression can also occur in individuals suffering from certain types of cancers or blood disorders.
The discovery has implications for blood transfusion safety. Patients who are AnWj-negative face potential life-threatening reactions if they receive AnWj-positive blood.
By identifying individuals who lack the AnWj antigen through the new genotyping test, doctors can ensure safer blood transfusions.
Nicole Thornton, Head of IBGRL Red Cell Reference addressed that this discovery will allow the development of genotyping tests that can be integrated into existing genotyping platforms.
These tests will make it easier to identify both AnWj-negative patients and potential blood donors, improving care for individuals with rare blood types.
The new genotyping test will make it easier to find blood donors for rare patients. The NHSBT handles about 400 rare cases each year globally.
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