The woman was preparing for surgery in a Paris hospital when doctors noticed something strange. Her blood didn’t match any known type. It wasn’t A, B, AB, or O. Nor did it fit any of the dozens of rarer classifications known to specialists.

Tests came back inconclusive. The hospital’s labs couldn’t determine what blood she could safely receive — or give.

That was in 2011.

Now, 14 years later, her blood is no longer a mystery. It is a new milestone.

In June 2025, researchers at France’s national blood agency announced that the woman carries a previously unknown blood group. It has been formally recognized as the 48th human blood group system, named “Gwada negative” after the patient’s Caribbean homeland of Guadeloupe.

“She is undoubtedly the only known case in the world,” said Thierry Peyrard, a medical biologist at Établissement français du sang (EFS), France’s national blood establishment. “She is the only person in the world who is compatible with herself.”

A Genetic Needle in a Haystack

When the patient first arrived in the clinic in 2011, doctors detected an unusual antibody in her blood. But with the tools available at the time, they could go no further.

So, the case went cold for years.

It wasn’t until 2019, with the help of newly available high-throughput DNA sequencing, that scientists could revisit her blood and sequence her entire genome. After two years of careful genetic analysis, researchers discovered a mutation in a gene called PIGZ.

This gene regulates how proteins anchor to the surface of red blood cells. In this woman’s case, the mutation disrupted that anchoring process in a way never seen before, producing a unique constellation of antigens on her blood cells.

The result: a blood group no existing system could classify.

The name “Gwada negative” honors the woman’s Guadeloupean heritage and, as Peyrard notes, “sounds good in all languages.” It also follows a blood group naming tradition whereby rare blood groups often bear the names of the people or places tied to their discovery.

Why Blood Groups Matter

Blood types are determined by antigens, which are specific molecules made of proteins or sugars that coat the surface of red blood cells. These antigens function a bit like ID cards. Your immune system uses them to distinguish between your own cells and potentially dangerous intruders.

The most familiar system, ABO, was discovered by Karl Landsteiner in 1901, earning him the Nobel Prize in 1930. In that system, people have the A antigen, the B antigen, both (AB), or neither (O). A second major system, Rhesus (Rh), classifies blood based on the presence (+) or absence (-) of another antigen known as the D antigen.

Together, these two systems produce the eight common blood types: A+, A−, B+, B−, AB+, AB−, O+, and O−.

But that’s only part of the picture. In reality, red blood cells can carry more than 600 different antigens, grouped into dozens of distinct systems. If a person’s immune system encounters an unfamiliar antigen during a blood transfusion, it may launch a dangerous attack. That’s why matching blood types is vital. Even a subtle mismatch can trigger a life-threatening immune response.

The International Society of Blood Transfusion (ISBT) tracks the systems used to classify these antigens. Until now, the ISBT recognized 47 group systems.

So, Gwada negative is now number 48.

Most transfusions — matched using the ABO and Rh systems — succeed 99.8% of the time. But when that 0.2% goes wrong, it often involves rare blood groups most people have never heard of.

“Discovering new blood groups means offering patients with rare blood a better level of care,” the EFS said in a statement.

When patients, like the woman in Paris, fall outside the standard categories, identifying the right blood type can mean the difference between life and death. Knowing her blood type now means she can receive safe transfusions, should she ever need them. But there’s a problem: no other donor has her blood.

She is, for now, an immunohematological island.

What Comes Next?

The research team is now turning its attention to Guadeloupe, hoping to find others who may carry the same mutation. Since blood types are genetic, they often cluster in families or populations. The woman inherited the mutated gene from both parents.

If others in the region carry even one copy of the variant gene, they might help researchers better understand how it works — and how common it might be in the Caribbean or elsewhere.

The discovery comes at a time when technology is rewriting the rules of what we can see in our biology. Since the ABO system was first discovered in 1901, researchers have slowly added new systems to the list. The pace was once glacial: only 45 systems had been recognized until just a few years ago.

But since 2022, scientists have been identifying more than one new blood group a year. One of the most recent, named “Er,” was confirmed just three years ago after a 50-year investigation.

Now, blood science is entering a new phase.

As sequencing becomes cheaper and faster, researchers expect more surprises. For now, “Gwada negative” is a reminder of how much remains hidden in plain sight, even in something as familiar as the blood that runs through us.