Scientists Solve 50 Year Blood Mystery With Discovery of New Human Blood Group

A Medical Detective Story Five Decades in the Making

In 1972, a routine blood test from a pregnant woman revealed something that would puzzle scientists for half a century. Her blood was mysteriously missing a surface molecule found on all other known red blood cells at the time. What started as a medical anomaly has finally been solved, leading researchers from the UK and Israel to identify an entirely new blood group system called MAL.

Louise Tilley, Senior Research Scientist at NHS Blood and Transplant, spent nearly two decades investigating the mystery personally. "The genetic background of AnWj has been a mystery for more than 50 years," she explained. The research was particularly difficult because inherited cases are so rare. Scientists would not have achieved this breakthrough without exome sequencing, as the gene they identified wasn't an obvious candidate.

Beyond A, B, and O: The Hidden Complexity of Human Blood

Most people think blood typing stops at the familiar A, B, AB, and O categories, plus the Rh factor. But human blood diversity extends far beyond these basic classifications. Scientists have now identified 47 blood group systems containing more than 360 known blood antigens. These antigens are molecules found on the surface of red blood cells, and even tiny differences between donors and recipients can sometimes trigger severe immune reactions.

The newly recognized MAL blood group system centers on the AnWj antigen, a rare blood marker first identified in 1972, with the name "AnWj" coming from the first patients found to produce the antibody, Anton and Wj. Previous research found that more than 99.9 percent of people have the AnWj antigen that was missing from the 1972 patient's blood.

Cracking the Genetic Code

Using whole exome sequencing, which analyzes all protein-coding regions of DNA, the team discovered that inherited AnWj-negative individuals carry deletions in both copies of the MAL gene. Because this antigen lives on a myelin and lymphocyte protein, the researchers named the newly described system the MAL blood group.

The breakthrough required sophisticated genetic detective work. To determine they had the correct gene, after decades of research, the team inserted the normal MAL gene into blood cells that were AnWj-negative, which effectively delivered the AnWj antigen to those cells. The MAL protein is known to play a vital role in keeping cell membranes stable and aiding in cellular transport.

Life-Saving Implications for Rare Patients

Now that the genetic markers behind the MAL mutation are known, patients can be tested to see if their negative MAL blood type is inherited or due to suppression – which could flag another underlying medical problem. Tilley and colleagues also identified three AnWj-negative patients without this mutation, suggesting some blood disorders can suppress the antigen.

This discovery has immediate practical benefits for patient safety. When someone lacking AnWj receives regular donor blood, their immune system attacks the transfused cells in reactions that happen fast and can be deadly. These rare blood quirks can have devastating impacts on patients, so the more of them we can understand, the more lives can be saved.

The MAL blood group discovery represents more than just another entry in medical textbooks. It demonstrates how advancing genetic technology continues to reveal hidden aspects of human biology, potentially improving transfusion safety for the rarest patients. As DNA sequencing becomes more sophisticated and accessible, researchers expect to uncover additional blood group variations that have remained invisible to medicine for decades.