Emm-negative: A new blood type found in only one person
In June 2025, the International Society of Blood Transfusion (ISBT) officially recognized the world's 48th human blood group system: Emm-negative. Informally referred to as 'Gwada negative,' after the Guadeloupean heritage of the only known individual with this blood type, the classification is unique. As French biologist Thierry Peyrard noted, 'She is the only person on the planet compatible with herself.'
The discovery dates back to 2011, when a 54-year-old woman underwent routine pre-operative screening. An unidentified antibody in her blood puzzled doctors. At the time, without the advanced genetic tools available today, the case was archived. Nearly a decade later, next-generation DNA sequencing uncovered a previously unknown mutation affecting the gene responsible for producing the EMM antigen, a molecule present on almost all human red blood cells.
The absence of this high-incidence antigen posed a significant challenge in transfusion medicine. Confirming the rarity and clinical implications of this finding required six additional years of peer-reviewed research. In June 2025, ISBT delegates in Milan unanimously agreed to classify Emm as a new and independent blood group system, now officially known as ISBT042.
Most people recognize their blood type by its ABO classification and Rh factor—positive or negative. However, red blood cells are adorned with dozens of other markers, or antigens, made from proteins, lipids, or sugars. The ISBT categorizes these into blood group systems, including the well-known Rh system and lesser-known groups like Vel.
The EMM antigen is considered a high-frequency antigen, meaning more than 99.99% of the global population has it. When this antigen is absent, as in the case of the Paris patient, the immune system may react aggressively to donor blood, potentially causing life-threatening hemolytic shock.
For the patient, this rare blood type means extreme caution. Any transfusion must be precisely matched to avoid immune complications. Her only option is autologous donation—banking her own blood ahead of planned medical procedures. This mirrors the situation for people with the Bombay blood group, another ultra-rare type first identified in 1952. While Bombay patients can sometimes find compatible donors globally, no such network yet exists for Emm-negative individuals.
The breakthrough came with next-generation sequencing, which allowed researchers to identify the exact gene deletion responsible for the missing EMM antigen. This technology, combined with expansive DNA databases, is rapidly accelerating the discovery of rare blood types—at least five new systems have been classified since 2012.
Rare blood types present serious logistical challenges. In the U.S., a unit of red blood cells typically costs around $225, excluding testing. For rare units, especially those deep-frozen for long-term storage, costs can soar to ten times that amount. Emergency situations involving rare blood types can incur thousands more in international shipping and delays that jeopardize lives.
The American Rare Donor Program already tracks about 100,000 individuals with uncommon antigen profiles. The addition of Emm-negative highlights the need for further expansion.
In response, French researchers have begun screening archived blood samples from Caribbean populations, hoping to identify additional Emm-negative donors. Even a small donor pool could provide essential reserves for future transfusion needs and emergencies.
In the long term, scientists are exploring lab-grown red blood cells made from stem cells engineered to match rare antigen profiles. Clinical trials are underway, with hopes of broader application within the next decade.
For now, the Paris woman who helped reveal the Emm-negative blood group continues her daily life — marked by a routine existence, yet with an extraordinary and singular designation on her medical record.
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