In a groundbreaking development, French scientists have identified the world’s rarest blood group, known as Gwada-negative. It’s a blood group so rare that only one woman in the world is known to have it.
The existence of the unique blood type was first suspected in 2011 during a pre-surgical screening, when clinicians at France’s national blood agency, the Établissement Français du Sang (EFS), noticed something strange about a Guadeloupean woman’s blood: it reacted against every donor sample, including that of close family members.
Later tests revealed something astonishing, she carried antibodies that didn’t match any known blood group in the world. The presence of this unfamiliar antibody presented the French scientists with a mystery that would take over a decade to solve.
The breakthrough came in 2019, when high-throughput DNA sequencing revealed a rare mutation in a gene called PIGZ. This particular gene encodes for an enzyme involved in the final step of producing glycosylphosphatidylinositol (GPI), a molecule essential for anchoring proteins to the surface of red blood cells.
In the case of the Guadeloupean woman, the absence of a specific sugar prevented proper formation of the EMM antigen. Without this antigen, her red blood cells triggered immune reactions when exposed to donor blood.
This wasn’t just a rare blood type. It was a new blood type. A discovery so unique that there is no known compatible donor in the global registry.
“She is the only person in the world who is compatible with herself,” said EFS medical biologist Thierry Peyrard.
Her case is a reminder that not all patients fit within established medical frameworks.
In June 2025, the International Society of Blood Transfusion (ISBT) recognized Gwada as the 48th blood group. It is scientifically known as ERYR, or EMM-negative, but in honor of the patient’s Caribbean roots, it has been nicknamed Gwada-negative – “Gwada” being slang for “from Guadeloupe”.
The implications of this rare blood type extend beyond emergent transfusion needs. Scientists have noted that the Guadeloupean woman suffers from a mild intellectual disability and has endured two stillbirths. Scientists at EFS suspect these abnormalities may be linked to the PIGZ mutation and its disruption of GPI biosynthesis. Similar enzyme defects are known to cause neurological and developmental issues, in addition to blood incompatibility.
To address the challenge of ultra-rare blood types, scientists are now exploring the possibilities of lab-grown blood using stem cell technology and gene editing. With genetic sequencing becoming cheaper and more widespread, discoveries like this may become more common. Each one brings us closer to a personalized model of medicine, where understanding our unique biology could directly shape how we are treated.
But this isn’t just a tale of one woman. It’s a significant reminder that medical systems are still catching up to the diversity of the human population. Many blood group systems beyond the familiar ABO and Rh types – especially among people of African and Caribbean descent, groups historically underrepresented in genomic research – remain poorly understood.
The Gwada-negative discovery could help change that. It may be the genesis of new modalities for diagnosing genetic disorders, tailoring transfusions, and even preparing for the future of personalized medicine. With each new rare blood type discovery, we learn more about how our genes shape health outcomes, improve transfusion safety, and deepen our understanding of human evolution, health risks, and disease susceptibility.
Source: The Conversation
