By Suherman Candra Maholtra 
The landscape of human biology has been fundamentally altered following a landmark discovery by a collaborative team of scientists in the United Kingdom. After more than half a century of scientific uncertainty, researchers have successfully identified the genetic origin of the AnWj blood group antigen, leading to the official establishment of MAL as the 47th human blood group system. This achievement, spearheaded by scientists at NHS Blood and Transplant (NHSBT) in Bristol, the International Blood Group Reference Laboratory (IBGRL), and the University of Bristol, resolves a medical enigma that has persisted since 1972. The discovery provides a vital molecular roadmap for identifying rare individuals who lack this specific antigen, thereby significantly reducing the risk of life-threatening transfusion reactions.
While the general public is most familiar with the ABO and Rh (Rhesus) systems, human hematology is governed by a much more intricate array of biological markers. Red blood cells are coated with hundreds of different molecules, many of which function as antigens—biological "flags" that the immune system uses to distinguish self from non-self. For the vast majority of the global population, these minor systems remain inconsequential. However, for the small fraction of individuals with rare blood types, the presence or absence of a single antigen can mean the difference between a successful medical procedure and a fatal immune response.
The Decades-Long Mystery of the AnWj Antigen
The story of the AnWj antigen began in 1972, when clinicians first identified a marker on human red blood cells that did not fit into any known classification at the time. Despite its discovery, the specific protein carrying the antigen and the gene responsible for its production remained elusive for over five decades.
Statistically, the AnWj antigen is nearly universal, present in more than 99.9% of the human population. Because of this ubiquity, the rare individuals who are "AnWj negative" face a unique medical peril. If an AnWj-negative person is exposed to AnWj-positive blood—either through a transfusion or during pregnancy—their immune system may recognize the antigen as a foreign invader and develop potent antibodies against it. In subsequent transfusions, these antibodies can launch a massive attack on the donor cells, leading to an acute hemolytic transfusion reaction, where the red blood cells are destroyed, potentially causing organ failure or death.
The challenge in solving this mystery lay in the dual nature of AnWj negativity. Most individuals who lack the antigen do so because of "suppression"—an acquired condition often linked to hematological disorders or specific types of cancer that interfere with the body’s ability to express the marker. Far more elusive are those who are "genetically" AnWj negative, meaning they were born without the ability to produce the antigen due to an inherited genetic mutation. Prior to this breakthrough, only a handful of such individuals had ever been documented, providing researchers with an incredibly small pool of genetic material to study.
Advanced Genetic Sequencing and the Discovery of the MAL Gene
To crack the case, the research team utilized whole exome sequencing, a sophisticated genomic technique that targets the protein-coding regions of the DNA. By sequencing the entire exome of the rare individuals known to be genetically AnWj negative, the scientists were able to search for shared mutations across thousands of genes.
The analysis led the team to the MAL gene, which provides instructions for creating the Mal protein (Myelin and Lymphocyte protein). The Mal protein is a small, highly specialized membrane protein involved in cellular transport and the organization of the cell’s outer boundary. The researchers discovered that every individual with the inherited AnWj-negative phenotype carried homozygous deletions in the MAL gene. In genetics, "homozygous" indicates that the individual inherited the same mutation from both parents, effectively "switching off" the production of the full-length Mal protein.
The study’s cohort included five genetically AnWj-negative individuals, including members of an Arab Israeli family. Notably, the researchers also analyzed a blood sample donated in 2015 by the very first woman identified as AnWj negative in the 1970s. This connection between the original discovery and modern genomic technology provided the definitive evidence needed to link the phenotype to the MAL gene.
Rigorous Validation through Laboratory Experimentation
Identifying a genetic association is only the first step in establishing a new blood group system; the researchers had to prove causality. To do this, the team at the University of Bristol employed advanced gene expression manipulation.
Scientists introduced the normal MAL gene into laboratory cell lines that did not previously express the antigen. Following this intervention, the cells began to react with AnWj antibodies, confirming that the presence of the Mal protein is what creates the AnWj-positive status. Conversely, when the team introduced the mutated version of the gene found in AnWj-negative patients, the cells remained non-reactive. These experiments demonstrated that the Mal protein is both necessary and sufficient for the expression of the AnWj antigen on the surface of red blood cells.
This level of proof is the gold standard in hematology. By connecting the serological observation (the reaction to antibodies) to a specific molecular structure (the Mal protein) and a specific genetic sequence (the MAL gene), the researchers fulfilled the requirements to propose a new blood group system.
Official 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 a distinct blood group system, assigning it the designation ISBT 047. This classification is a major milestone in transfusion medicine.
The field of hematology is currently experiencing a period of rapid expansion driven by genomic technology. MAL was one of four systems ratified during the ISBT’s 2026 terminology report cycle, joined by the ER, CD36, and ATP11C systems. Shortly thereafter, in September 2026, the ISBT announced the discovery of JAMA as the 49th blood group system. This rapid succession of discoveries underscores that the biological map of human blood is far more complex than previously understood, with many rare markers still being integrated into clinical practice.
Clinical Implications: Transforming Patient Care
The primary benefit of this discovery is the ability to develop reliable genotyping tests. Previously, identifying an AnWj-negative patient or donor required complex and rare antibody testing, which is often only available in specialized reference laboratories. With the MAL gene identified, healthcare providers can now use DNA-based screening to identify these rare individuals quickly and accurately.
The clinical necessity for such testing is underscored by recent medical cases. In 2026, researchers documented a 75-year-old man suffering from severe anemia who had developed an anti-AnWj autoantibody. Because compatible blood could not be found, doctors were forced to perform an "unmatched" transfusion, weighing the risk of a reaction against the immediate threat of anemia. In this instance, genetic testing confirmed his MAL gene was normal, suggesting his lack of AnWj was an acquired condition rather than an inherited one, which helped clinicians manage his treatment strategy.
In another complex 2026 case, a patient with high-grade B-cell lymphoma experienced red blood cell destruction (hemolysis) following a transfusion due to anti-AnWj antibodies. Clinicians treated the patient with sutimlimab, a monoclonal antibody that inhibits the C1s enzyme in the immune complement pathway. This represented the first reported use of sutimlimab to manage AnWj-related hemolysis, offering a potential new therapeutic avenue for patients when perfectly matched blood is unavailable.
Perspectives from the Research Team
The resolution of the AnWj mystery is the result of decades of persistence. Louise Tilley, Senior Research Scientist at the IBGRL, noted the personal significance of the breakthrough. "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 stated. "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."
Ash Toye, Professor of Cell Biology at the University of Bristol, highlighted the role of modern biotechnology in solving historical puzzles. "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 said. He emphasized that the development would directly aid in identifying rare donors for future patients.
Nicole Thornton, Head of IBGRL Red Cell Reference, emphasized the global impact of the work. "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, making these discoveries for the benefit of rare patients around the world," she said. Thornton confirmed that genotyping tests for MAL can now be integrated into existing blood screening platforms.
Conclusion: A New Era in Transfusion Safety
The identification of the MAL blood group system marks the end of a 50-year "cold case" in human biology. By moving AnWj from a mysterious serological observation to a genetically defined system, researchers have provided the medical community with the tools to prevent rare but devastating transfusion reactions.
As blood centers around the world begin to incorporate MAL genotyping into their screening protocols, the safety of the global blood supply will continue to improve. This discovery serves as a powerful reminder of the hidden complexities within the human body and the vital importance of international collaboration in the pursuit of medical science. For the rare individuals who are AnWj negative, the world has just become a significantly safer place.
