What began as a strange lab result in a pregnant woman’s blood has ended in the formal recognition of a brand‑new human blood group system, one so rare that almost everyone on Earth carries the opposite type.
A mystery hidden in a 1972 blood sample
Back in 1972, doctors examined a pregnant woman whose red blood cells seemed to be missing a surface molecule that every other tested person had. No one could explain it. The sample was unusual, but technology at the time could not reveal much more, so the case lingered in the background of transfusion medicine for decades.
That missing molecule has now been traced to a protein called MAL, leading scientists from the UK and Israel to define a new blood group system, officially recognised in 2024. The work connects that puzzling case from half a century ago with modern genetics and cell biology.
After more than 50 years, scientists have turned a single odd result into a clearly defined, ultra‑rare blood group known as MAL.
Far beyond A, B, and O
Most people only know their blood type as something like A+, O−, or B+. Those letters come from the ABO system, while the plus or minus refers to the Rh factor. Yet these are only two out of dozens of recognised blood group systems, each based on different molecules that decorate the surface of red blood cells.
These surface molecules, called antigens, act a bit like ID badges. The immune system checks them to distinguish between “self” and “foreign”. If blood from a donor carries antigens that the recipient’s immune system does not recognise, antibodies in the recipient’s plasma can attack the transfused cells.
When blood antigens do not match between donor and recipient, even a life‑saving transfusion can turn dangerous.
Most of the major blood groups, including ABO and Rh, were characterised early in the 20th century, when doctors started to understand why some transfusions failed. Since then, more subtle and rare blood group systems have been catalogued, each affecting only a tiny number of people. MAL now joins that list.
What makes the MAL blood group different
The newly recognised MAL system centres on a specific antigen called AnWj. Earlier work showed that more than 99.9 percent of people carry AnWj on their red blood cells. That 1972 patient did not, making her what scientists now call AnWj‑negative.
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The MAL protein itself sits in cell membranes and helps keep them stable. It is also involved in moving molecules around within cells. The AnWj antigen appears on this protein, but not straight away in life: researchers have observed that newborns do not have detectable AnWj on their red cells at birth. The antigen appears shortly afterwards, suggesting that the MAL system switches on in early infancy.
How genetics creates a rare blood type
Researchers finally pinpointed the cause of the missing AnWj by looking directly at the MAL gene. When both copies of this gene carry a particular mutation, the MAL protein does not display the AnWj antigen properly, and the person is AnWj‑negative.
That mutation pattern was shared by all the inherited AnWj‑negative individuals studied in the research. To prove that MAL was the key, scientists inserted a normal, working MAL gene into AnWj‑negative blood cells in the lab. Once MAL was restored, AnWj appeared on the cell surface.
By restoring the normal MAL gene in the lab, researchers switched the missing AnWj antigen back on, clinching the case for a new blood group system.
The team also uncovered a second route to the same blood type. Three additional patients were AnWj‑negative but did not carry the same MAL mutation. In those cases, blood disorders appeared to suppress the expression of the antigen, even though the MAL gene itself was intact.
Why such a rare blood group still matters
AnWj‑negative people are vanishingly rare, but that does not mean their blood is unimportant. For them, routine medical care can turn complex quickly. If someone who is AnWj‑negative receives blood packed with the AnWj antigen, their immune system may react strongly, destroying the donor red cells and triggering fever, low blood pressure, or kidney damage.
The impact of the discovery goes beyond a handful of patients. It also gives hospitals better tools to interpret unexpected transfusion reactions and pregnancy complications. When a blood test flags an anomaly, clinicians can now check whether a MAL‑related issue is involved.
- People with two mutated MAL genes: inherited AnWj‑negative blood type
- People with normal MAL but no AnWj: possible suppression by another blood disorder
- People with normal MAL and AnWj present: the overwhelming majority of the population
With the genetic marker identified, labs can screen for MAL mutations rather than relying only on complex antibody tests. That helps distinguish a lifelong, inherited blood type from a temporary loss of the antigen linked to an underlying illness.
How MAL fits into modern transfusion practice
Transfusion services already juggle many blood group systems when matching donors and recipients. For most patients, ABO and Rh matching, along with a standard antibody screen, are enough. The MAL system will mainly come into play for people with rare serological patterns or past unexplained reactions.
Blood banks that specialise in rare donor registries may now start flagging known AnWj‑negative donors, much as they do for other scarce types. Even a small pool of correctly typed donors can be lifesaving for a patient who cannot safely receive standard blood products.
Rare blood groups turn into critical problems only at the exact moment a patient needs blood and nothing seems to match.
Researchers also note that the MAL mutation identified in AnWj‑negative individuals was not linked to obvious disease or structural defects in blood cells. That suggests people with this inherited type can live normal, healthy lives, with the main risk arising when they require transfusion or certain pregnancy care.
Key terms and ideas worth unpacking
Antigens and antibodies, in plain language
Antigens are molecules on the surface of cells, including red blood cells. They act like name tags. An antigen such as AnWj tells your immune system, “I belong here.” Antibodies are Y‑shaped proteins circulating in blood plasma. They recognise specific antigens and latch on to those that look foreign.
During a transfusion, if your antibodies find antigens they have never seen before, they may attack the donor cells. This is why a person with a rare blood group might need blood from someone with a nearly identical antigen pattern.
What might this mean for patients in real life?
Consider a patient who has received several transfusions over many years. At some point, lab staff notice that standard matches keep triggering weak reactions, and cross‑matching becomes increasingly difficult. With MAL now on the radar, doctors can request genetic testing for the MAL gene and AnWj status. If the patient is AnWj‑negative, targeted donor searches can prevent stronger reactions later on.
Pregnancy is another scenario. If a pregnant person is AnWj‑negative and their fetus inherits a different MAL pattern, antibodies produced during pregnancy might target fetal red cells. While such cases would be extremely rare, recognising the MAL system allows obstetric teams to watch more closely and plan care.
For people who are simply curious about their blood type, MAL testing will not become part of routine screening any time soon. The cost and complexity do not justify it for the general public. For a small number of patients with puzzling transfusion histories, though, this new blood group gives doctors a sharper tool and another explanation to consider.