World’s Rarest Blood Group: Gwada-Negative
In a routine blood test that turned extraordinary, French scientists have identified the world’s newest and rarest blood group . The sole known carrier is a woman from Guadeloupe whose blood is so unique that doctors couldn’t find a single compatible donor.
The discovery of the 48th recognised blood group, called “Gwada-negative”, began when the woman’s blood plasma reacted against every potential donor sample tested, including those from her own siblings. Consequently, it was impossible to find a suitable blood donor for her.
Most people know their blood type – A, B, AB or O – along with whether they are Rh-positive or negative. But these familiar categories (those letters plus “positive” or “negative”) represent just two of several dozens of blood group systems that determine compatibility for transfusions. Each system reflects subtle but crucial differences in the proteins and sugars coating our red blood cells.
To solve the mystery of the Guadeloupian woman’s incompatible blood, scientists turned to cutting-edge genetic analysis. Using whole exome sequencing – a technique that examines all 20,000-plus human genes – they discovered a mutation in a gene called PIGZ.
This gene produces an enzyme responsible for adding a specific sugar to an important molecule on cell membranes. The missing sugar changes the structure of a molecule on the surface of red blood cells. This change creates a new antigen – a key feature that defines a blood group – resulting in an entirely new classification: Gwada-positive (having the antigen) or -negative (lacking it).
Using gene editing technology, the team confirmed their discovery by recreating the mutation in a lab. So red blood cells from all blood donors tested are Gwada-positive and the Guadeloupean patient is the only known Gwada-negative person on the planet.
The implications of the discovery extend beyond blood transfusions. The patient suffers from mild intellectual disability, and tragically, she lost two babies at birth – outcomes that may be connected to her rare genetic mutation.
The enzyme produced by the PIGZ gene operates at the final stage of building a complex molecule called GPI (glycosylphosphatidylinositol). Previous research has shown that people with defects in other enzymes needed for GPI assembly can experience neurological problems ranging from developmental delays to seizures. Stillbirths are also common among women with these inherited disorders.
Although the Caribbean patient is the only person in the world so far with this rare blood type, neurological conditions including developmental delay, intellectual disability and seizures have been noted in other people with defects in enzymes needed earlier in the GPI assembly line.
The Gwada discovery highlights both the marvels and challenges of human genetic diversity. Blood groups evolved partly as protection against infectious diseases (many bacteria, viruses and parasites use blood group molecules as entry points into cells). This means your blood type can influence your susceptibility to certain diseases.
But extreme rarity creates medical dilemmas. The French researchers acknowledge they cannot predict what would happen if Gwada-incompatible blood were transfused into the Guadeloupian woman. Even if other Gwada-negative people exist, they would be extremely difficult to locate. It is also unclear if they can become blood donors.
This reality points towards a futuristic solution: lab-grown blood cells. Scientists are already working on growing red blood cells from stem cells that could be genetically modified to match ultra-rare blood types. In the case of Gwada, researchers could artificially create Gwada-negative red blood cells by mutating the PIGZ gene.
Gwada joins 47 other blood group systems recognised by the International Society of Blood Transfusion. Like most of these blood-group systems, it was discovered in a hospital lab where technicians were trying to find compatible blood for a patient.
The name reflects the case’s Caribbean roots: Gwada is slang for someone from Guadeloupe, giving this blood group both scientific relevance and cultural resonance.
As genetic sequencing becomes more advanced and widely used, researchers expect to uncover more rare blood types. Each discovery expands our understanding of human variation and raises fresh challenges for transfusion and other types of personalised medicine.
Martin L Olsson is a Wallenberg Clinical Scholar who receives research funding from Knut and Alice Wallenberg Foundation (grant no. 2020.0234). He holds other major grants from the Swedish Research Council (grant no. 2024-03772), the Novo Nordisk Foundation (grant no. NNF22OC0077684) and the Swedish government funds to university healthcare for clinical research (ALF grant no. 2022.0287). He is also a member of the International Society of Blood Transfusion (ISBT)’s Working Party on Red Cell Immunogenetics and Blood Group Terminology.
Jill Storry receives funding from the Swedish Research Council (grant no. 2024-03772). She is affiliated with, and the current senior Vice-President, of the International Society of Blood Transfusion, as well as a member of the society’s Working Party on Red Cell Immunogenetics and Blood Group Terminology.