YOUR BLOOD TYPE ISN’T JUST A, B, AB OR O.
Scientists solved a blood mystery that had been sitting inside the human body for more than fifty years. And the answer reveals just how incomplete our everyday idea of “blood type” really is.
Ask someone their blood type and, if they know it at all, the answer will probably sound familiar. A positive. O negative. AB positive. One of eight combinations most of us were taught somewhere along the way. And none of that is wrong. It is simply nowhere near the whole story. Because while most of us have been walking around thinking humanity has eight blood types, scientists have been cataloguing an enormously more complicated landscape of molecules sitting on the surfaces of our red blood cells.
As of September 2026, the International Society of Blood Transfusion recognizes 49 separate blood-group systems. Its current database contains hundreds of recognized blood-group antigens.
Yes, you read that correctly. Forty-nine separate blood-groups. And one of those systems exists because of a tiny biological mystery first noticed more than half a century ago. In 1972, researchers identified an unusual red-blood-cell antigen that eventually became known as AnWj. They knew it existed. They could detect antibodies against it. They knew that almost everybody had it. What they did not know was what gene actually produced it. That question remained unresolved for more than fifty years. Then researchers finally found the answer. And in doing so, they established an entirely new human blood-group system. Its name is MAL.
FIRST: YOUR BLOOD TYPE IS MUCH BIGGER THAN YOU THINK
The familiar A, B, AB and O labels describe one blood-group system: ABO. The positive or negative sign most of us attach to it usually refers to another: Rh, specifically whether the RhD antigen is present. Put those together and we get the familiar eight: A+, A−, B+, B−, AB+, AB−, O+ and O−.
But your red blood cells carry many other surface markers called antigens. Think of them, very loosely, as biological identification markers. Your immune system pays attention to those markers. And that becomes extremely important when somebody else’s blood enters your body.
If transfused red cells carry an antigen your immune system recognizes as foreign—and you have antibodies capable of attacking it—the immune response can destroy those cells and potentially cause a serious transfusion reaction. That is why blood matching can become considerably more complicated than simply checking whether the bag says O+ or A-.
For most routine situations, ABO and RhD do a tremendous amount of the work. For certain patients—especially people who receive repeated transfusions, develop unusual antibodies, or have exceptionally rare antigen combinations—the rest of the blood-group map can suddenly matter enormously. And that brings us back to AnWj.
THE 1972 MYSTERY
AnWj is what scientists call a high-prevalence antigen. That description is almost comically understated. More than 99.9% of people are AnWj-positive, meaning their red blood cells carry this antigen. Then there is that extraordinarily tiny number of people who do not. And those rare AnWj-negative people created a fascinating problem. Scientists could see the phenotype—the observable blood characteristic—but they could not identify the genetic machinery behind it.
For decades, researchers investigated possible explanations. There were clues. There were candidate genes. There were associations. But the actual genetic basis remained unresolved. One of the researchers who eventually helped solve it, Louise Tilley of NHS Blood and Transplant’s International Blood Group Reference Laboratory, had personally worked on the problem for almost twenty years.
Then modern genetic sequencing gave the team another way in. They studied people with the extraordinarily rare inherited AnWj-negative phenotype using whole-exome sequencing—a technique that examines the protein-coding portions of DNA. And something appeared. The rare inherited cases carried deletions involving a gene called MAL. That gene produces a small membrane protein called Mal.
Researchers then found something crucial: AnWj-positive red blood cells expressed the full-length Mal protein. AnWj-negative cells did not. Interesting. But interesting isn’t proof. So they kept going. And before we get to what finally proved it, there’s an obvious question: If this matters, why isn’t your doctor testing you for it? Because for almost everyone, there is no reason to.
The inherited AnWj-negative phenotype is extraordinarily rare. Only five genetically AnWj-negative people were included in the study that established MAL as a blood-group system.
Routine blood typing is designed around what is clinically useful for the overwhelming majority of patients. But when someone has an unusual red-cell antibody, difficulty finding compatible blood, a history that warrants further investigation, or another clinical reason for more specialized testing, blood-bank and reference laboratories can go considerably deeper. And the MAL discovery gave those laboratories something they did not previously have: A genetic target.
Researchers can now design genotyping tests to identify genetically AnWj-negative patients and donors, potentially helping locate compatible blood and reduce transfusion complications for the extraordinarily rare people who need it.
So no—this isn’t another screening test everybody needs at their annual physical. It’s a test that could matter enormously to the extraordinarily rare person who needs it. That distinction matters.
THEN THEY DID THE EXPERIMENT THAT MATTERED
The researchers introduced the normal MAL gene into laboratory cells. Those cells began expressing the AnWj antigen. In other words, adding the functioning gene caused the mysterious blood marker to appear. Additional antibody experiments pointed to the same conclusion. Mal wasn’t merely hanging around somewhere near AnWj. The evidence showed that the Mal protein was necessary and sufficient for AnWj expression.
Fifty-plus years after scientists first encountered the antigen, they finally knew what they were looking at. The mystery had a gene. The gene had a protein. And the protein had a place on the human blood-group map.
The result became the MAL blood-group system, formally recognized as the 47th human blood-group system. That is the scientific part of the story. The medical part may be even more important.
WHY THE HELL DOES THIS MATTER?
Because rare does not mean irrelevant.
Imagine being one of the extraordinarily small number of people who inherited the AnWj-negative phenotype. Your red blood cells lack an antigen carried by more than 99.9% of the population. If your immune system has developed antibodies against AnWj and you receive AnWj-positive blood, those antibodies may react with the transfused cells. And almost every donor around you is AnWj-positive.
Suddenly, finding compatible blood is not a matter of checking the giant A, B, AB or O letter printed on the bag. It becomes a search for a biological needle in a human haystack.
Knowing the gene changes that search. Now laboratories can develop genotyping tests to identify genetically AnWj-negative patients and potential donors instead of relying solely on specialized antibody testing. That can help blood services locate compatible donors and reduce the risk of transfusion complications for the rare patients who need them.
And there is another wrinkle. Not everybody who tests AnWj-negative was born that way. Researchers report that AnWj expression can also be suppressed in association with some hematological disorders and certain cancers. That distinction matters. A person can therefore appear AnWj-negative because of an acquired suppression of the antigen—or belong to the extremely rare group whose AnWj-negative status is inherited through changes in MAL. The genetic discovery gives doctors another tool for telling those situations apart.
AND HERE IS WHERE THIS STORY GETS REALLY FUCKING INTERESTING.
MAL wasn’t the end. When MAL was recognized in 2024, it became blood-group system number 47. By June 2026, the official database contained 48 systems. And this year researchers added another. JAMA. On September 14, 2026, the International Society of Blood Transfusion announced that JAMA had become the 49th recognized blood-group system.
Read that again. Not 49 blood types in the ordinary A-positive/O-negative sense. Forty-nine different classification systems describing inherited red-cell antigens. The distinction matters. But so does the larger point. JAMA was identified after researchers investigated blood from an Israeli woman and her brother. Scientists combined traditional serology with whole-exome sequencing and traced a previously unresolved high-prevalence antigen to variation in the F11R gene, which encodes the JAM-A protein.
So the fifty-year AnWj mystery wasn’t some bizarre historical leftover finally swept off the laboratory floor. It belongs to an active field in which researchers are still identifying pieces of human blood biology.
The map is still being written. And perhaps that is the strangest part. We are still discovering fundamental differences in human blood in 2026. Not in some organism pulled from the bottom of an unexplored ocean. Not in a fossil. Not on another planet. In us. In the same human body medicine has examined, dissected, transfused, scanned, sequenced and studied for centuries. Which raises a much bigger question: How much else about ourselves have we mistaken for fully understood simply because we understand part of it?
LET’S LOOK DEEPER.
There is something wonderfully humbling about this. Human beings have transfused blood for generations. We have sequenced the human genome. We can edit genes. We can grow tissues in laboratories. We can peer billions of light-years into space. And we are still discovering exactly what is sitting on the surface of the red blood cells moving through our own veins. Or do we?
That does not mean medicine has no idea how blood works. Quite the opposite. Modern transfusion medicine works because scientists have painstakingly identified these differences and built systems for detecting them. But it does mean the simplified version most of us learned— A. B. AB. O. Positive. Negative. —is exactly that. A simplified version. Useful. Important. And incomplete.
Your everyday blood type is not your entire blood identity. It is the part of an extraordinarily complicated biological classification system that most of us happen to encounter.
SO DO YOU HAVE A SECRET BLOOD TYPE?
Probably not in the dramatic sense that headline would suggest. If someone tells you they are O+, they are still O+. Discovering MAL did not invalidate ABO or Rh. It added another layer to what scientists know about red-cell biology.
But the human story behind that discovery may be just as interesting as the genetics. The 2024 study examined only five genetically AnWj-negative individuals, including members of an Arab-Israeli family. The investigation was led by scientists at NHS Blood and Transplant’s International Blood Group Reference Laboratory in Bristol, working with the University of Bristol and international collaborators.
And one blood sample connected the investigation all the way back to the beginning. The researchers tested a sample donated in 2015 by the woman who had been the first AnWj-negative person identified in the 1970s. Think about that. A biological difference first noticed in one person’s blood remained an unanswered scientific question for more than half a century. The person existed. The unusual blood existed. The antigen existed. The answer existed somewhere in the biology. Science simply didn’t yet have the complete explanation. Then genetics caught up. And that’s what makes extremely rare cases valuable far beyond the handful of people who carry them.
Rare people can reveal common biology. Medicine doesn’t investigate rare blood merely because rare things are interesting. Outliers can expose biological machinery that is almost invisible precisely because it works normally in nearly everybody else. And remarkably, the story is already repeating itself.
In September 2026, the International Society of Blood Transfusion recognized JAMA as blood-group system 49. That discovery also began with unusual blood—this time samples from an Israeli woman and her brother. Researchers combined serology with whole-exome sequencing and traced the previously unresolved antigen to variation in F11R, the gene encoding the JAM-A protein.
Different people. Different antigen. Different gene. Same scientific lesson: Sometimes the exception is the thing that shows us how the rule actually works
IS AnWj-NEGATIVE BLOOD ACTUALLY SPECIAL?
Rare? Extremely. Superhuman? There is absolutely no evidence of that. There is currently no established evidence that genetically AnWj-negative people heal faster, resist infections better, live longer, think differently, possess different neurological abilities, or receive some other biological advantage from lacking the antigen.
What researchers have established is clinically important enough without embellishment. AnWj is carried on the Mal protein, and antibodies against AnWj can be clinically significant. If an AnWj-negative person has developed anti-AnWj antibodies and receives AnWj-positive blood, a transfusion reaction can occur. That is why identifying those rare patients—and finding compatible donors—matters.
But here’s the part that makes this even stranger: Being AnWj-negative does not necessarily mean you were born that way. Researchers say the more common reason someone becomes AnWj-negative is suppression of the antigen associated with certain hematological disorders or some cancers.
The inherited MAL-related form is the exceptionally rare one. So AnWj-negative blood isn’t a secret superior version of human blood. It isn’t evidence of unusual immunity, extraordinary healing or some hidden human ability. Its importance is much more concrete. If you are one of the extraordinarily rare people for whom this antigen matters, knowing about it could help doctors find blood your immune system can safely accept. And in transfusion medicine, that isn’t trivia. That can be lifesaving.
SHOULD YOU ASK YOUR DOCTOR TO TEST YOU FOR MAL?
For the average healthy person, probably not. There is currently no evidence that knowing your AnWj status provides some general health advantage or predicts healing ability, longevity, intelligence, consciousness or resistance to disease.
Where MAL becomes important is transfusion medicine—particularly when someone has an unusual red-cell antibody, difficulty finding compatible blood, or another clinical reason for specialized blood-group investigation. If that happens, MAL stops being obscure science. It could become the difference between blood that is compatible and blood that isn’t.
WHAT WE KNOW
AnWj was identified in 1972, but its genetic basis remained unresolved for more than fifty years. Researchers eventually traced the inherited AnWj-negative phenotype to deletions in the MAL gene. The Mal protein is expressed on AnWj-positive red blood cells and absent from AnWj-negative cells.
More than 99.9% of people are AnWj-positive.
The discovery established MAL as blood-group system 47 and created a genetic route for identifying extremely rare AnWj-negative patients and donors. And the field did not stop there. As of September 2026, 49 blood-group systems are recognized by ISBT, with JAMA the newest addition.
WHAT WE STILL DON’T FUCKING KNOW
Finding the genetic basis of MAL does not mean every question about the system has been answered. Because inherited AnWj-negativity is so rare, researchers have had very few genetically confirmed people to study.
We do not yet know exactly how many genetically AnWj-negative people exist worldwide. We do not know whether future screening will reveal populations or families in which the phenotype occurs more frequently. And MAL itself was one more reminder that unresolved blood-group antigens can remain scientifically stubborn for decades before genetics, serology and enough extraordinarily rare human samples finally line up.
The answer to a fifty-year mystery therefore produced something better than closure. It produced another way to look.
THE RECEIPTS.
FFE: The original peer-reviewed MAL study was published in Blood by Louise Tilley and colleagues: “Deletions in the MAL gene result in loss of Mal protein, defining the rare inherited AnWj-negative blood group phenotype.”
FFE: The research was led by NHS Blood and Transplant’s International Blood Group Reference Laboratory, with collaborators including the University of Bristol and institutions in Israel.
FFE: The official international registry is maintained by the International Society of Blood Transfusion, whose current database recognizes 49 blood-group systems.
FFE: Read the original MAL study in Blood. Deletions in the MAL gene result in loss of Mal protein, defining the rare inherited AnWj-negative blood group phenotype
FFE: NHS Blood and Transplant — MAL discovery. NHS Blood and Transplant-led team discovers new blood group system MAL
International Society of Blood Transfusion — current blood-group database. Blood Group Database
FFE: ISBT — JAMA becomes blood-group system 49. Meet JAMA: the 49th ISBT blood group system
DON’T TAKE OUR FUCKING WORD FOR IT.
READ THE RECEIPTS.
Because perhaps the strangest thing about this story isn’t that scientists needed more than fifty years to solve it. It’s that the answer had been there the entire time. On our cells. In our genes. Moving through human veins with every heartbeat. We just hadn’t learned how to read it yet.
Same facts. Different perspectives.
Let’s look deeper. 🩸
