New blood type discovered after 50 years of mystery

When a pregnant woman’s blood was drawn in 1972, doctors discovered that a surface molecule found on all other red cells known at the time was mysteriously missing.

After 50 years, this strange molecular absence finally led researchers in the UK and Israel to describe a new blood group system in humans. In 2024, the team published their paper on the new discovery.

“It is a huge achievement and the culmination of a long team effort to finally establish this new blood group system and to be able to provide the best care for rare but important patients.”

This was said by haematologist Louise Tilley, of the UK’s National Health Service, after almost 20 years of personal research into this strange blood group.

More blood types?

Although we are all most familiar with the ABO blood group system and the Rh factor (plus or minus), humans actually have several different blood group systems based on the wide variety of cell surface proteins and sugars that coat our red cells.

Our bodies use these antigen molecules, among their other purposes, as identification markers to separate “self” from potentially harmful non-self.

If these markers do not match when a blood transfusion is received, this lifesaving tactic can cause reactions or even be fatal.

Most of the important blood groups were identified in the early 20th century.

Many more have been discovered since then, such as the Er blood type, first described by researchers in 2022, but which only affects a small number of people. This is also the case with the new blood type.

“The research was difficult because genetic cases are very rare,” Tilley explained.

New blood type: MAL

Previous studies have found that more than 99.9% of people have the AnWj antigen that was missing from the 1972 patient’s blood.

This antigen lives on a myelin and lymphocyte protein, which led the researchers to name the newly described system the MAL blood group.

When someone has a mutated version of both copies of the MAL genes, they end up with an AnWj-negative blood type, like the pregnant patient.

Tilley and his team identified three patients with the rare blood type who did not have this mutation, suggesting that sometimes blood disorders can also cause antigen suppression.

“MAL is a very small protein with some interesting properties that made it difficult to identify and showed us that we needed to pursue several lines of investigation to accumulate the evidence we needed to establish this group system,” explained Tim Satchwell, a cell biologist at the University of the West of England.

To determine whether they had the correct gene, after decades of research, the team introduced the normal MAL gene into red cells that were AnWj-negative. This effectively delivered the AnWj antigen to those cells.

MAL mutation – an anomaly?

The MAL protein is known to play a vital role in maintaining cell membranes and supporting cellular transport. Furthermore, previous research has found that AnWj is not actually present in newborns, but appears shortly after birth.

Interestingly, all of the AnWj-negative patients included in the study shared the same mutation. However, no other cellular abnormalities or diseases were found to be associated with this mutation.

Now that researchers have identified the genetic markers behind the MAL mutation, patients can be tested to see if their MAL negative blood type is inherited or is due to suppression, which could be a sign of another underlying medical problem.

These rare blood quirks can have devastating effects on patients, so the more we can understand about them, the more lives can be saved.

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Source: sciencealert.com, thebiomedicalscientist.net, bbc.com.

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