By Suherman Candra Maholtra 
In a landmark achievement for hematology and transfusion medicine, researchers have finally identified the genetic source of a mysterious blood marker that has puzzled the scientific community for more than half a century. The breakthrough, led by scientists at NHS Blood and Transplant (NHSBT) in Bristol, in collaboration with the International Blood Group Reference Laboratory (IBGRL) and the University of Bristol, has officially established MAL as the world’s 47th human blood group system. This discovery provides a long-awaited molecular explanation for the AnWj-negative phenotype, a condition so rare that it has eluded genetic characterization since the antigen was first detected in 1972.
The resolution of this biological mystery is not merely an academic milestone; it carries profound implications for clinical safety. By identifying the MAL gene as the blueprint for the protein carrying the AnWj antigen, medical professionals can now utilize targeted genetic testing to identify rare patients and donors. This capability is critical for preventing life-threatening transfusion reactions in individuals whose immune systems would otherwise view standard donor blood as a foreign threat.
The Half-Century Search for the AnWj Antigen
The story of the AnWj antigen began in 1972, when clinicians first encountered a patient whose blood lacked a specific surface marker found in the vast majority of the human population. At the time, while the ABO and Rh systems were well-understood, the broader landscape of human blood group systems was still being mapped. For decades, the AnWj antigen remained a "serological curiosity"—it could be detected through traditional antibody testing, but its genetic origin and the specific protein that carried it remained unknown.
Statistically, more than 99.9% of the global population is AnWj-positive. The antigen is nearly ubiquitous, meaning that almost every human carries this marker on their red blood cells. However, for the infinitesimal minority of individuals who are AnWj-negative, the stakes are incredibly high. If an AnWj-negative person is exposed to AnWj-positive blood—either through a transfusion or during pregnancy—their immune system may develop potent antibodies against the antigen. Subsequent exposure can trigger a hemolytic transfusion reaction, where the body’s immune system systematically destroys the donor red blood cells, leading to severe complications or death.
The primary obstacle to solving this mystery was the extreme rarity of the inherited AnWj-negative phenotype. While some individuals become AnWj-negative temporarily due to hematological disorders or certain types of cancer—where the expression of the antigen is suppressed—those who are born without the antigen due to genetic factors are exceptionally hard to find. Over five decades, only a handful of such individuals were identified worldwide, leaving researchers with a very limited pool of genetic material to study.
The Role of Whole Exome Sequencing in Genomic Discovery
The breakthrough finally arrived through the application of whole exome sequencing (WES), a sophisticated genomic technique that focuses on the protein-coding regions of the DNA. Because the exome represents less than 2% of the human genome but contains about 85% of known disease-causing variants, it is a powerful tool for identifying the causes of rare genetic conditions.
The research team analyzed the DNA of several AnWj-negative individuals, including members of an Arab Israeli family and the original patient identified in the 1970s, who had provided a blood sample as recently as 2015. The analysis revealed a consistent pattern: all individuals with the inherited AnWj-negative phenotype carried homozygous deletions in the MAL gene.
In genetics, a homozygous deletion means that the specific genetic instruction is missing from both copies of the gene—one inherited from the mother and one from the father. The MAL gene is responsible for producing the Mal protein (Myelin and Lymphocyte protein), a small, highly hydrophobic integral membrane protein. Prior to this study, the Mal protein was known to play a role in membrane organization and the sorting of proteins within cells, but it had never been associated with red blood cell antigens.
Experimental Validation: Proving the MAL Connection
To confirm that the MAL gene was indeed the source of the AnWj antigen, the researchers conducted a series of rigorous laboratory experiments. The team utilized gene-editing technology to manipulate the expression of the Mal protein in developing blood cells.
In the first phase of validation, the researchers introduced a normal, functional MAL gene into laboratory-grown cells that did not naturally express the AnWj antigen. Following this introduction, the cells began to react positively with AnWj antibodies, proving that the presence of the Mal protein was sufficient to create the antigen. Conversely, when the team introduced the mutated or deleted versions of the gene found in AnWj-negative patients, the cells remained non-reactive.
Additional experiments demonstrated that the Mal protein is essential for the antigen’s presence on the cell surface. These findings provided the "smoking gun" evidence required by international regulatory bodies to recognize a new blood group system. The study proved that the AnWj antigen is not merely a passenger on the protein but is fundamentally tied to the protein’s structure.
Formal Recognition and the Expanding Map of Human Blood
Following the publication of the team’s findings, the International Society of Blood Transfusion (ISBT) formally ratified MAL as a distinct blood group system, assigning it the designation ISBT 047. This classification places MAL alongside other recently discovered systems such as ER, CD36, and ATP11C.
The pace of discovery in this field has accelerated rapidly. By late 2026, the ISBT reported the addition of JAMA as the 49th blood group system. This ongoing expansion highlights a fundamental truth in modern medicine: human blood is far more complex than the standard A, B, AB, and O categories taught in introductory biology. As of 2026, there are now nearly 50 recognized blood group systems containing hundreds of individual antigens.
For a marker to be elevated to the status of a "blood group system," it must meet strict criteria, including the identification of the gene responsible for the antigen and evidence that the antigen is inherited. The MAL discovery met all these requirements, transforming it from a clinical observation into a genetically defined diagnostic category.
Clinical Case Studies and the Impact on Patient Care
The practical necessity of this discovery is underscored by recent clinical reports. In 2026, a case study emerged involving a 75-year-old male patient suffering from severe anemia and possessing an anti-AnWj autoantibody. Because compatible blood was non-existent in the local and national registries, physicians were forced to proceed with an unmatched transfusion after a careful risk-benefit analysis. Genetic testing facilitated by the new MAL discovery confirmed that his MAL gene was normal, indicating that his AnWj-negative status was acquired due to his underlying health condition rather than inherited.
In another complex case from 2026, a patient with high-grade B-cell lymphoma developed a complement-binding anti-AnWj antibody. After initial transfusions led to signs of hemolysis (red blood cell destruction), clinicians turned to sutimlimab, a monoclonal antibody designed to inhibit the C1s enzyme in the classic complement pathway. This marked the first recorded use of sutimlimab to manage anti-AnWj-associated hemolysis. While the results were promising, researchers noted that more data is needed to confirm the drug’s efficacy in these rare scenarios.
These cases illustrate the two-fold challenge clinicians face: identifying patients who are genetically AnWj-negative from birth and managing those who become AnWj-negative due to disease. The discovery of the MAL gene allows for the development of genotyping platforms that can quickly distinguish between these two groups, ensuring that rare blood units are reserved for those with a permanent genetic need.
Perspectives from the Research Team
The successful identification of the MAL system was the result of decades of persistence. Louise Tilley, a Senior Research Scientist at IBGRL who has dedicated nearly 20 years of her career to this specific puzzle, described the achievement as the culmination of a massive team effort.
"The genetic background of AnWj has been a mystery for more than 50 years," Tilley stated. "It represents a huge achievement to finally establish this new blood group system and be able to offer the best care to rare, but important, patients. The work was difficult because the genetic cases are so rare. We would not have achieved this without exome sequencing, as the gene we identified wasn’t an obvious candidate."
Ash Toye, Professor of Cell Biology at the University of Bristol, emphasized the role of modern technology in solving historical cold cases in biology. "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 these rare donors will significantly improve the safety of blood banks worldwide.
Nicole Thornton, Head of IBGRL Red Cell Reference, highlighted the global implications 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. Now genotyping tests can be designed to identify genetically AnWj-negative patients and donors."
The Future of Transfusion Medicine and Rare Donor Registries
The identification of the MAL blood group system marks a turning point in the field of transfusion medicine. Prior to this discovery, identifying an AnWj-negative donor required labor-intensive serological screening, which involved testing blood samples against rare antibodies that were themselves in short supply.
With the genetic sequence of MAL now known, blood services can integrate AnWj screening into existing high-throughput genotyping platforms. This allows for the proactive screening of thousands of donors to find the "one in a thousand" individuals who lack the antigen. These donors can then be added to international rare donor registries, such as those maintained by the World Health Organization (WHO) and the ISBT.
Furthermore, this discovery opens new avenues for research into the Mal protein itself. While its role in red blood cells is now established as the carrier of the AnWj antigen, its broader physiological functions in the human body remain a subject of interest. As scientists continue to map the "dark matter" of the human genome, the resolution of the MAL mystery serves as a testament to the power of collaborative science and the persistence of the human spirit in the face of long-standing biological puzzles.
For the rare patients who live with the knowledge that their blood type is one of the rarest on Earth, the discovery of the MAL system offers more than just a name—it offers the security of a safer medical future. As genomic technology continues to advance, the medical community moves closer to a day when every patient, no matter how unique their biological profile, can receive a safe and compatible blood transfusion.
