Researchers have solved a 50-year-old mystery by discovering a new blood group system called MAL.

Scientists from NHS Blood and Transplant (Bristol), the International Blood Group Reference Laboratory (IBGRL) and the University of Bristol first identified the genetic basis of the mysterious AnWj blood group antigen.

This breakthrough will help identify and treat patients who lack this rare blood group.

While some people may temporarily lose this antigen due to disease, the hereditary absence of AnWj is extremely rare and has been found in only a small number of individuals worldwide. Thanks to this discovery it will now be easier to identify other people with this condition.

Blood group systems like ABO and Rh are well known, but blood is more complex and matching with other groups can be lifesaving. There are many other important blood group markers. Mismatches in rare groups such as AnWj can cause serious transfusion-related reactions.

This research enables better testing to detect individuals with this rare blood type, reducing the risk of complications.

The AnWj antigen was first discovered in 1972, but its genetic origin has remained unknown until now. Research published in the journal Blood shows that AnWj is based on a protein called Mal.

More than 99.9% of people have the AnWj antigen because they produce the full-length MAl protein on their red blood cells. In contrast, AnWj-negative individuals lack this protein due to a deletion in the MAL gene.

The study found that most people who are AnWj-negative have underlying health problems, such as blood disorders or certain cancers, that suppress expression of the antigen.

Only a small number of individuals are genetically AnWj-negative, including a family of Arab-Israeli descent.

The researchers used whole exome sequencing, a technique that examines protein-coding regions of DNA, to identify the deletion in the MAL gene responsible for the absence of AnWj.

They confirmed their findings by reintroducing a normal MAL gene into cells, which restored the antigen.

Lewis Tilley, senior research scientist at IBGRL, called the discovery an important milestone after two decades of effort, highlighting the importance of teamwork and advanced genetic tools.

Ash Toy of the University of Bristol emphasized how gene manipulation techniques played a key role in solving this long-standing puzzle.

The discovery of the MAL blood group system is a step toward improving care of patients with rare blood types and paves the way for better diagnostic tools and treatment options in the future.