After five decades of unanswered questions, scientists from the UK and Israel have finally identified a new blood group system in humans. This discovery, published in September, solves a medical mystery that began in 1972 when doctors encountered a pregnant woman whose blood lacked a key surface molecule found on all other known red blood cells at the time.
“This represents a huge achievement and the culmination of a long team effort,” said Louise Tilley, a hematologist with the UK National Health Service.
Tilley has dedicated nearly 20 years of her career to understanding this rare blood phenomenon.
“We can now offer the best care to rare, but important, patients.”
What Are Blood Group Systems?
While most people are familiar with the ABO blood group system and the rhesus factor (the “positive” or “negative” designation), there are many more blood group systems based on proteins and sugars that coat the surface of red blood cells. These molecules, called antigens, play a vital role in helping the body distinguish between its own cells and potential threats.
However, if the antigens on donor blood do not match those of the recipient, transfusions can cause dangerous reactions or even be fatal. This is why understanding rare blood types is crucial for patient safety.
The MAL Blood Group System
The newly identified blood group system has been named “MAL,” after the myelin and lymphocyte protein that carries the missing AnWj antigen. The discovery explains why the 1972 patient’s blood was different: she had a rare mutation in both copies of her MAL genes, making her AnWj-negative.
“Previous research found that more than 99.9% of people have the AnWj antigen. But in rare cases, people with a specific MAL gene mutation do not,” explained Tilley.
The researchers identified three other patients with this rare blood type. Interestingly, in some cases, the absence of the AnWj antigen was not caused by a genetic mutation but by blood disorders that suppress the antigen.
Solving a Decades-Long Puzzle
The journey to identify the MAL blood group was complex and spanned decades.
“MAL is a very small protein with some interesting properties which made it difficult to identify. We had to pursue multiple lines of investigation to gather enough evidence to establish this new blood group system,” said Tim Satchwell, a cell biologist at the University of the West of England.
The breakthrough came when researchers inserted a normal MAL gene into blood cells that were AnWj-negative. This process successfully restored the AnWj antigen, confirming the role of the MAL protein.
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Implications for Patients
The MAL protein is known to stabilize cell membranes and assist in cell transport. Scientists also found that the AnWj antigen is absent in newborns but develops shortly after birth.
Interestingly, all patients with the AnWj-negative blood type in the study shared the same mutation. However, no other health issues or abnormalities were linked to this mutation.
Now that the genetic markers for the MAL mutation are identified, doctors can test patients to determine whether their AnWj-negative status is inherited or caused by other medical conditions. If suppression of the antigen is found, it could indicate an underlying health problem requiring further investigation.
Saving Lives Through Research
This discovery highlights the importance of studying rare blood group systems.
“These rare blood quirks can have devastating impacts on patients. The more we understand them, the more lives we can save,” Tilley emphasized.