For more than half a century, one strange clue about human blood sat unexplained in medical records: a molecule that seemed to be missing from a patient’s blood cells, with no known reason why. Now, researchers have finally cracked the case — and in doing so, added an entirely new blood group system to the map of human biology.
The Mystery That Started With One Pregnant Woman in 1972
Every scientific mystery needs an origin point, and this one begins in 1972, when a pregnant woman had her blood sampled during a routine test. Doctors ran the sample and found something odd: it was missing a surface molecule found on the red blood cells of virtually everyone else tested at the time.
That missing molecule was eventually named the AnWj antigen — a marker found on the surface of almost all human red blood cells. For the next fifty years, that single unexplained gap in one woman’s blood sample became one of hematology’s most stubborn open questions. Scientists knew the antigen existed. They knew a vanishingly small number of people didn’t have it. What they didn’t know, for five decades, was why.
That changed with new research from NHS Blood and Transplant’s International Blood Group Reference Laboratory (IBGRL) in Bristol, working with the University of Bristol and several international partners. The team finally identified the genetic cause behind the elusive AnWj marker — closing a scientific case file that had been open since before most people reading this article were born.
Meet MAL: The 47th Human Blood Group System
If your only exposure to blood types came from high school biology, you probably learned about two systems: ABO (A, B, AB, O) and Rh (the positive or negative that gets tacked onto your blood type). What most people don’t realize is that those are just two of dozens of blood group systems scientists have identified on the surface of human red blood cells.
This new discovery adds one more to that list — and it has a name: MAL.
Researchers traced the AnWj antigen back to a specific gene, called MAL, which produces a protein of the same name. That protein — formally known as myelin and lymphocyte-associated protein — is what carries the AnWj marker on the surface of red blood cells. Once scientists confirmed this genetic link through laboratory testing, the discovery was significant enough to earn formal recognition: the International Society of Blood Transfusion designated MAL as an official human blood group system, ISBT 047 — the 47th distinct blood group system ever formally recognized.
For context on just how rare this condition is: more than 99.9% of people worldwide carry the AnWj antigen on their red blood cells. The vanishingly small minority who don’t are the very same “medical mystery” patients whose blood confounded doctors for half a century, one strange test result at a time.
Why It Took 50 Years to Solve
If the answer was sitting in a single gene, a reasonable question is: why did this take five decades to figure out?
The honest answer is scarcity. Louise Tilley, Senior Research Scientist at IBGRL Red Cell Reference at NHS Blood and Transplant, has explained that investigating the genetic background of AnWj proved exceptionally difficult precisely because so few people affected by it exist. Modern genetic research typically relies on studying multiple affected individuals to identify shared genetic patterns with confidence — and when your entire eligible study population worldwide might amount to a handful of documented cases, that kind of pattern-matching becomes enormously harder.
Nicole Thornton, head of the Bristol laboratory where much of this research took place, has similarly emphasized that unraveling the AnWj mystery represented a considerable challenge for the team — a fitting understatement for a puzzle that outlasted entire careers in hematology. It’s worth pointing out that this wasn’t fifty years of active, continuous research — it was fifty years of an unanswered question resurfacing periodically, worked on in fits and starts as new genetic sequencing technology gradually became powerful enough to make the answer findable.
Two Very Different Reasons to Lack AnWj
One of the more clinically important nuances to come out of this research is the discovery that people can lack the AnWj antigen for two genuinely different reasons — and the distinction matters enormously for patient care.
The first, and far more common, explanation is acquired absence: AnWj expression can be suppressed in someone who otherwise has the normal gene, usually due to an underlying blood disorder or certain cancers. In these cases, the antigen isn’t genetically missing — it’s temporarily suppressed by an unrelated medical condition.
The second, far rarer explanation is inherited absence: some people are born permanently without the AnWj antigen because they carry an inherited deletion affecting both copies of their MAL gene. Unlike the acquired form, this version is a lifelong, genetically fixed trait, present from birth and unrelated to any current illness.
That distinction is exactly the kind of clinical nuance blood banks and hematologists need in order to treat patients safely — because the medical risks that come with lacking AnWj don’t disappear just because the underlying cause differs.
When Missing an Antigen Becomes Dangerous
For the overwhelming majority of the 99.9%+ of people who carry the AnWj antigen normally, none of this changes anything about their day-to-day health or transfusion needs. But for the small number of AnWj-negative patients, this discovery could be genuinely lifesaving.
People whose blood lacks the AnWj antigen can develop antibodies against it — meaning their immune system treats AnWj-positive blood, the kind carried by virtually everyone else, as a foreign threat. If an AnWj-negative patient receives a transfusion of ordinary AnWj-positive blood, it can trigger a dangerous transfusion reaction, as their immune system attacks the incoming red blood cells.
Recent case reports from 2026 illustrate just how serious these complications can be. In one documented case, a 75-year-old man with severe anemia and an anti-AnWj autoantibody had to receive unmatched red blood cells simply because no compatible, AnWj-negative blood was available at the time. In another case involving a patient with high-grade B-cell lymphoma who had developed a complement-binding anti-AnWj autoantibody, clinicians turned to sutimlimab — a drug that blocks part of the body’s immune complement pathway — after incompatible transfusions triggered signs that the patient’s red blood cells were being destroyed.
These aren’t hypothetical scenarios. They’re real patients who faced genuine danger during routine medical care, precisely because doctors had no reliable way to identify or screen for AnWj-negative blood before this discovery.
What This Means for Blood Banks Going Forward
This is where the science translates directly into practical, lifesaving change. Before this discovery, doctors had no genetic test capable of reliably identifying AnWj-negative individuals in advance — they largely discovered someone was AnWj-negative only after a dangerous reaction had already occurred, or through painstaking, specialized laboratory antibody testing that isn’t part of routine blood screening.
Now, knowing the exact gene responsible gives blood specialists something they never had before: a direct genetic method for identifying people who are AnWj-negative before a medical emergency forces the issue. A genetic test built around this discovery can be incorporated into existing donor and patient genotyping platforms already used by blood banks — meaning rare AnWj-negative patients could eventually be flagged proactively, and rare AnWj-negative donors could be identified and recruited to build up a reserve supply for exactly the kind of emergency transfusion scenarios described above.
For a healthcare system that already carefully matches blood type, Rh factor, and a range of other rarer markers before every transfusion, adding a reliable genetic test for MAL status closes a genuine, previously invisible gap in patient safety.
A Field That’s Still Rapidly Expanding
It would be easy to assume that after this discovery, the map of human blood groups is now essentially complete. It isn’t — and the pace of new discoveries happening right alongside this one proves it.
MAL was just one of four new blood group systems formally ratified by the International Society of Blood Transfusion during the period covered by its 2026 terminology report, alongside three others named ER, CD36, and ATP11C. And the field hasn’t slowed down since: in September 2026, the International Society of Blood Transfusion announced JAMA as the 49th officially recognized human blood group system — a sign that the genetic map of human blood is still actively being redrawn, decades after most people assumed the basics had long since been settled.
For something to formally qualify as a recognized blood group system, researchers have to do more than simply notice a marker exists — they need to connect that antigen to a defined, confirmed genetic and molecular basis, exactly the kind of work that took fifty years in AnWj’s case and, apparently, considerably less time for some of these newer additions, thanks to how far genetic sequencing technology has advanced since 1972.
Why This Story Resonates Beyond Medicine
Part of what makes a story like this so compelling isn’t just the clinical significance — it’s the reminder that something as seemingly basic and well-understood as “what’s my blood type” is actually a far deeper and more complex biological question than most people realize.
Nearly everyone assumes they fully understand their own blood type once they’ve heard “A positive” or “O negative” at some point in their life. In reality, red blood cells carry dozens of distinct antigen systems beyond ABO and Rh — most of which never come up in a person’s lifetime unless something rare occurs, like needing a transfusion during a medical emergency and discovering, unexpectedly, that your blood doesn’t match what the textbooks assumed applies to everyone.
This discovery closes one fifty-year-old chapter of that ongoing story. But as the rapid addition of new blood group systems throughout 2026 shows, it’s very unlikely to be the last surprise hiding in something as familiar as the blood running through all of our veins.
