By Suherman Candra Maholtra 
The identification of the genetic source of the AnWj blood group antigen marks the end of a 50-year scientific quest, providing a definitive molecular explanation for a marker first detected in 1972. Led by a collaborative team from NHS Blood and Transplant (NHSBT) in Bristol, the International Blood Group Reference Laboratory (IBGRL), and the University of Bristol, the research has officially established MAL as a new human blood group system. This discovery provides clinicians with the necessary tools to identify rare individuals who lack the AnWj antigen, thereby preventing life-threatening transfusion reactions and improving the precision of hematological diagnostics.
While the ABO and Rhesus (Rh) systems are the most widely recognized blood classifications, human red blood cells are far more complex, decorated with hundreds of distinct antigens. These molecules, which can be proteins or sugars, serve as biological signatures that the immune system uses to distinguish self from non-self. When a patient requires a blood transfusion, matching these antigens is critical. If a recipient’s immune system encounters a foreign antigen it does not possess, it may produce antibodies to attack the donor cells, leading to a hemolytic transfusion reaction. For the vast majority of the global population, the AnWj antigen is a permanent fixture on their red blood cells. However, for the infinitesimal minority who are AnWj-negative, receiving standard blood can be a gamble with their lives.
The Decades-Long Search for AnWj
The AnWj antigen was first identified in 1972, yet for more than five decades, its genetic blueprint remained elusive. Scientists knew the antigen existed because they could detect antibodies against it in certain patients, but they could not pinpoint the specific protein that carried the marker or the gene responsible for its production. This lack of genetic information meant that there was no way to screen for AnWj-negative individuals using DNA testing; instead, labs had to rely on rare, labor-intensive serological reagents that were often in short supply.
The mystery was compounded by the fact that AnWj-negativity is exceptionally rare. More than 99.9% of the population is AnWj-positive. Among the few who lack the antigen, there are two distinct categories. The first and most common group consists of individuals whose AnWj expression is suppressed due to underlying medical conditions, such as hematological disorders or specific types of cancer. The second group, which is far rarer, consists of individuals who are born AnWj-negative due to an inherited genetic mutation. Prior to this study, only a handful of people with the inherited form had ever been identified worldwide, leaving researchers with very little biological material to study.
Utilizing Whole Exome Sequencing to Crack the Code
To solve the puzzle, the research team employed whole exome sequencing, a high-tech genomic approach that focuses on the protein-coding regions of the DNA. By sequencing the exomes of the few known inherited AnWj-negative individuals—including a sample provided in 2015 by the very first patient identified in the 1970s—the researchers looked for commonalities that were absent in the general population.
The analysis led the team to the MAL gene. They discovered that individuals with the inherited AnWj-negative phenotype possessed homozygous deletions in this gene. In genetics, "homozygous" means the individual inherited the same mutation from both parents, effectively "switching off" the gene’s ability to function. The MAL gene is responsible for producing the Mal protein (Myelin and Lymphocyte protein), a small, highly hydrophobic membrane protein.
The researchers observed that while the Mal protein was present on the red blood cells of 99.9% of the population, it was entirely absent in those with the rare inherited AnWj-negative profile. To confirm their findings, the team used advanced gene-editing techniques to introduce the normal MAL gene into laboratory cell lines. Once the gene was expressed, the cells became reactive to AnWj antibodies, proving that the Mal protein is the essential carrier of the AnWj antigen.
Formal Recognition and the Expanding Map of Human Blood
Following the publication of these findings, the International Society of Blood Transfusion (ISBT) formally recognized MAL as the 47th blood group system, assigning it the designation ISBT 047. This classification is a major milestone in transfusion medicine, as it moves the AnWj marker from a poorly understood serological curiosity to a genetically defined system.
The field of blood group discovery has accelerated rapidly in recent years due to advancements in genomic sequencing. MAL was ratified alongside other systems such as ER, CD36, and ATP11C. By September 2026, the ISBT had already announced the identification of JAMA as the 49th system. This rapid expansion highlights the ongoing effort to map the full spectrum of human biological diversity, ensuring that even the rarest blood types are understood and accounted for in clinical settings.
Clinical Implications and Recent Case Studies
The ability to genetically test for the MAL gene has immediate practical applications. Blood centers can now develop genotyping assays to screen donors and patients for the AnWj-negative status. This is particularly vital because finding compatible blood for an AnWj-negative patient is a logistical nightmare; since 99.9% of donors are incompatible, a match may only be found through international rare donor registries.
The clinical necessity of this discovery is illustrated by recent medical cases. In 2026, a 75-year-old man presented with severe anemia and an anti-AnWj autoantibody. Because no compatible blood could be found, doctors were forced to perform an "unmatched" transfusion, a high-risk procedure. Genetic testing eventually revealed his MAL gene was normal, confirming his AnWj-negative status was acquired due to his health condition rather than inherited. This distinction is crucial for determining long-term treatment strategies.
In another complex 2026 case, a patient with high-grade B-cell lymphoma developed a complement-binding anti-AnWj antibody. After standard transfusions led to signs of red blood cell destruction (hemolysis), clinicians turned to sutimlimab, a monoclonal antibody that inhibits the C1s enzyme in the immune system’s complement pathway. This marked the first reported use of sutimlimab to manage anti-AnWj-associated hemolysis. The patient’s stabilization following this treatment suggests a new pathway for managing patients with rare antibodies when compatible blood is unavailable.
Statements from the Research Team
The resolution of the AnWj mystery is the result of decades of persistence. Louise Tilley, Senior Research Scientist at IBGRL Red Cell Reference, reflected on the personal and professional significance of the work. "The genetic background of AnWj has been a mystery for more than 50 years, and one which I personally have been trying to resolve for almost 20 years of my career," Tilley said. "It represents a huge achievement, and the culmination of a long team effort, to finally establish this new blood group system and be able to offer the best care to rare, but important, patients."
The difficulty of the project was echoed by Ash Toye, Professor of Cell Biology at the University of Bristol. "It’s really exciting we were able use our ability to manipulate gene expression in the developing blood cells to help confirm the identity of the AnWj blood group," Toye noted. He emphasized that the Mal protein was not an obvious candidate for a blood group antigen, making the validation process through gene editing essential for the scientific community to accept the findings.
Nicole Thornton, Head of IBGRL Red Cell Reference, highlighted the global impact of the discovery. "There is so much work that goes into proving that a gene does actually encode a blood group antigen, but it is what we are passionate about," Thornton stated. "Now genotyping tests can be designed to identify genetically AnWj-negative patients and donors. Such tests can be added to the existing genotyping platforms."
A New Era for Rare Donor Identification
The identification of the MAL blood group system serves as a reminder of the hidden complexities within the human body. For most people, blood type is a simple matter of A, B, or O, but for those with rare phenotypes, these "minor" blood groups are a matter of survival.
The Mal protein itself is now a subject of further study. While its role in red blood cells is now clear, it is also known to be involved in membrane organization and cellular transport in other tissues. Understanding why certain diseases suppress the expression of this protein could lead to broader insights into hematology and oncology.
For the global medical community, the establishment of MAL as ISBT 047 provides a new level of certainty. It allows for the creation of standardized diagnostic protocols and ensures that the handful of inherited AnWj-negative individuals—and those who develop the antibody due to illness—receive the most informed care possible. Five decades after the first clue was found in a lab, the mystery of AnWj is finally solved, paving the way for a safer and more precise future in transfusion medicine.
