By Suherman Candra Maholtra 
The landscape of human hematology has been fundamentally altered following a breakthrough discovery by a collaborative team of researchers in the United Kingdom. Led by scientists at NHS Blood and Transplant (NHSBT) in Bristol, in conjunction with the International Blood Group Reference Laboratory (IBGRL) and the University of Bristol, the team has successfully identified the genetic source of the AnWj blood group antigen. This discovery marks the official establishment of the MAL blood group system, solving a biological puzzle that has confounded the medical community since the antigen was first detected in 1972. By identifying the MAL gene as the blueprint for the protein carrying the AnWj antigen, researchers have provided clinicians with the tools necessary to identify rare individuals at risk of life-threatening transfusion reactions.
For over half a century, the AnWj antigen remained a "serological curiosity"—a marker known to exist on the surface of red blood cells but one that lacked a defined genetic or molecular home. While the ABO and Rh systems are the most widely recognized blood groups, they represent only a fraction of the complex surface chemistry of human erythrocytes. The recognition of MAL as the 47th official blood group system highlights the ongoing evolution of genomic medicine and its direct application to patient safety in transfusion science.
The Half-Century Search for the AnWj Source
The story of the AnWj antigen began in 1972 when hematologists first identified a patient whose blood lacked a specific marker found in the overwhelming majority of the human population. This marker was eventually named the AnWj antigen. Statistically, more than 99.9% of people are AnWj-positive, meaning their red blood cells express this specific protein. However, for the infinitesimal minority who are AnWj-negative, the absence of this marker is a critical medical detail.
If an AnWj-negative individual is exposed to AnWj-positive blood—either through a transfusion or during pregnancy—their immune system may recognize the antigen as a foreign invader. This can lead to the development of alloantibodies. If that person requires a subsequent transfusion, these antibodies can launch a massive attack on the donor cells, resulting in a hemolytic transfusion reaction. Such reactions can range from mild fever to acute kidney failure or even death.
Despite the clinical importance of the antigen, the specific gene responsible for its production remained elusive for decades. The primary obstacle was the extreme rarity of the inherited AnWj-negative phenotype. Because so few people are born with this condition, scientists lacked a sufficient pool of genetic material to conduct traditional linkage studies. The mystery persisted until the advent of whole exome sequencing (WES) provided the technological bridge needed to cross this decades-old gap.
The Genetic Breakthrough: Pinpointing the MAL Gene
The research team employed whole exome sequencing to analyze the protein-coding regions of the DNA of a small group of AnWj-negative individuals. This group included a member of an Arab Israeli family and, notably, a blood sample donated in 2015 by the very woman who was first identified as AnWj-negative in the 1970s. By comparing these rare genomes against the general population, the researchers identified a common thread: homozygous deletions in the MAL gene.
The MAL gene is responsible for producing the Mal protein (Myelin and Lymphocyte protein), a small, highly hydrophobic integral membrane protein. While the Mal protein was known to play a role in the organization of "lipid rafts" and cellular transport in various tissues, its presence and significance on red blood cells had never been fully explored. The researchers discovered that while AnWj-positive individuals possessed full-length Mal protein on their red cell membranes, the protein was entirely absent in those with the inherited AnWj-negative phenotype.
To confirm that the MAL gene was indeed the source of the AnWj antigen, the team performed a series of sophisticated laboratory experiments. Using gene-editing techniques, they introduced the normal MAL gene into cells that did not naturally express the antigen. Following this intervention, the cells began to react with AnWj antibodies, proving that the Mal protein was both necessary and sufficient for the antigen’s expression. Conversely, introducing the mutant or deleted form of the gene failed to produce a reaction, solidifying the causal link.
Clinical Implications: Inherited vs. Acquired Phenotypes
One of the most significant aspects of the study is the distinction it draws between the two ways a person can become AnWj-negative. The researchers clarified that the inherited form, caused by the MAL gene deletion, is exceptionally rare, with only a handful of cases documented globally.
However, a much larger (though still small) group of people can become "transiently" AnWj-negative. This usually occurs as a secondary effect of an underlying medical condition, such as certain types of leukemia, lymphoma, or other hematological disorders that suppress the expression of the antigen on the cell surface.
The ability to genetically distinguish between these two groups is a major clinical advancement. For a patient with an acquired AnWj-negative status due to cancer, the treatment focus remains on the primary disease. For an individual with the inherited MAL deficiency, the focus is on lifelong transfusion management and the identification of compatible donors within their family or through international rare donor registries.
Recent Case Studies and the Role of Sutimlimab
The practical necessity of this discovery was underscored by clinical cases reported as recently as 2026. In one instance, a 75-year-old man presenting with severe anemia was found to have an anti-AnWj autoantibody. Because compatible blood could not be sourced in time, doctors had to proceed with an unmatched transfusion. While genetic testing eventually showed his MAL gene was normal—confirming his condition was acquired rather than inherited—the case highlighted the high-stakes pressure clinicians face when dealing with rare blood markers.
In another 2026 case, a patient suffering from high-grade B-cell lymphoma developed a complement-binding anti-AnWj autoantibody. When standard incompatible transfusions led to evidence of red cell destruction (hemolysis), doctors turned to an innovative solution: sutimlimab. This drug, a monoclonal antibody that inhibits the C1s protein in the immune system’s complement pathway, was used to successfully mitigate the destruction of transfused cells. This represented the first recorded use of sutimlimab for this specific type of hemolysis, offering a potential new pathway for treating patients with rare antibodies when compatible blood is unavailable.
Official Recognition and the Expanding Map of Human Blood
Following the publication of these findings, the International Society of Blood Transfusion (ISBT) formally ratified MAL as the 47th human blood group system (designated ISBT 047). This designation is reserved for antigens that have been definitively linked to a specific gene and protein structure.
The 2026 ISBT terminology report also noted the rapid expansion of the field, with the ratification of three other systems: ER, CD36, and ATP11C. Shortly thereafter, in September 2026, JAMA was announced as the 49th system. This surge in discovery reflects the power of modern genomic tools in resolving long-standing mysteries in human biology. The MAL system, however, remains unique due to the 50-year duration of its "homeless" status and the specific challenges posed by the Mal protein’s small size and complex membrane structure.
Statements from the Research Team
The resolution of the AnWj mystery has been described by those involved as the culmination of decades of persistence. Louise Tilley, Senior Research Scientist at the IBGRL Red Cell Reference, noted the personal significance of the achievement. "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. She emphasized that the breakthrough was a "team effort" that would finally allow for the "best care to rare, but important, patients."
Professor Ash Toye, Director of the NIHR Blood and Transplant Research Unit at the University of Bristol, highlighted the role of technology in the discovery. "It’s really exciting we were able to use our ability to manipulate gene expression in developing blood cells to help confirm the identity of the AnWj blood group," Toye said. He noted that the ability to identify rare donors is perhaps the most immediate benefit of the work.
Nicole Thornton, Head of IBGRL Red Cell Reference, pointed out the future-facing applications of the research. "Now genotyping tests can be designed to identify genetically AnWj-negative patients and donors," she explained. "Such tests can be added to existing genotyping platforms," making it easier for blood banks around the world to screen for these rare individuals during routine testing.
Broader Impact on Transfusion Medicine and Future Research
The identification of the MAL blood group system has several far-reaching implications for the global medical community:
- Enhanced Screening: Blood services can now develop DNA-based tests to screen for the MAL gene deletion. This is significantly faster and more accurate than older serological methods, which required rare, specialized antibodies that were in short supply.
- Global Rare Donor Registries: By identifying more AnWj-negative donors through genotyping, international registries can increase their stocks of compatible blood, which can be frozen and shipped across borders in emergencies.
- Insights into Cell Biology: The discovery that the Mal protein is essential for the AnWj antigen opens new avenues for research into the protein’s function on red blood cells. Given its role in "lipid rafts," researchers may now investigate whether the Mal protein affects how red cells interact with pathogens or handle oxidative stress.
- Diagnostic Precision: Clinicians can now quickly determine if a patient’s AnWj-negative status is a permanent genetic trait or a temporary symptom of a disease like lymphoma, allowing for more tailored treatment plans.
As the genetic map of human blood continues to be filled in, the resolution of the MAL system stands as a testament to the importance of collaborative science. It bridges the gap between the observational hematology of the early 1970s and the high-precision genomic medicine of the 2020s. For the rare individuals whose lives depend on finding a "one-in-a-thousand" match, this 50-year-old mystery finally reaching its conclusion is more than a scientific milestone—it is a vital safeguard for the future.
