Decades-Old Mystery Solved: Scientists Discover New Human Blood Group System
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A decades-long investigation sparked by a puzzling anomaly in a 1972 blood sample has culminated in the identification of a new human blood group system, offering crucial insights for rare transfusion cases and potentially uncovering hidden medical conditions. Researchers from the United Kingdom and Israel published their findings in 2024, marking a significant advancement in hematological science.
The Curious Case of the Missing Antigen
The story began with a pregnant woman whose blood sample, analyzed in 1972, lacked a surface molecule present in all other known red blood cells at the time. For over 50 years, this anomaly remained a medical curiosity. Now, that initial observation has led to the formal description of a previously unknown blood group system. “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,” said a hematologist from the UK National Health Service, who dedicated nearly two decades to researching this unusual case.
Beyond ABO and Rh: The Complexity of Blood Groups
While most people are familiar with the ABO blood group system and the Rh factor (positive or negative), human blood is far more complex. Numerous other blood group systems exist, defined by a diverse array of antigen molecules – proteins and sugars – coating the surface of red blood cells. These antigens act as identifiers, allowing the body to distinguish between “self” and potentially harmful “non-self.”
Mismatches in these markers during blood transfusions can trigger dangerous reactions, even proving fatal. Most major blood groups were identified in the early 20th century, but discoveries continue, often revealing systems present in only a small fraction of the population, like the Er system described in 2022. The newly identified blood group falls into this category of rarity.
Unveiling the MAL Blood Group
Researchers discovered that over 99.9% of people possess the AnWj antigen. Its absence in the 1972 patient’s blood proved pivotal. Because the antigen resides on a myelin and lymphocyte protein, the team named the new system the MAL blood group. Individuals with two mutated copies of the MAL gene lack the AnWj antigen, resulting in an AnWj-negative blood type, mirroring the original 1972 case.
Interestingly, researchers also identified three AnWj-negative patients without the gene mutation, suggesting that certain blood disorders can suppress the antigen’s expression. “The work was difficult because the genetic cases are very rare,” explained a lead researcher.
Decades of Research and Genetic Confirmation
Identifying the MAL blood group proved challenging. “MAL is a very small protein with some interesting properties which made it difficult to identify and meant we needed to pursue multiple lines of investigation to accumulate the proof we needed to establish this blood group system,” noted a cell biologist from the University of the West of England.
To definitively pinpoint the responsible gene, the team inserted the normal MAL gene into AnWj-negative blood cells, successfully restoring the antigen. The MAL protein is crucial for maintaining cell membrane stability and facilitating cellular transport. Notably, the AnWj antigen isn’t present in newborns, appearing shortly after birth.
Implications for Patient Care and Future Research
All AnWj-negative patients studied shared the same mutation, and no other associated health problems were identified. However, the discovery has significant clinical implications. Now, patients can be tested to determine if their AnWj-negative status is inherited or due to antigen suppression, potentially indicating an underlying medical condition.
These rare blood variations can have severe consequences for patients, underscoring the importance of continued research. As a senior official stated, “These rare blood quirks can have devastating impacts on patients, so the more of them we can understand, the more lives can be saved.”
The research was published in the journal Blood. An earlier version of this article appeared in September 2024.
