Researchers identify a new set of blood types

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If the ABO and Rhesus systems are the best known (and most used) blood group classification systems, you should know that there are actually dozens of ways to group red blood cells according to the molecules (sugars, proteins) they carry on their surface, called antigens Scientists from the NHS Blood and Transplant (NHSBT) and the University of Bristol have discovered a new blood group system, called Er. This is the 44th blood group system to date.

Unfortunately, sad circumstances led to this discovery. An unborn child was showing signs of distress, so the medical team at the British hospital where the mother was admitted decided to perform an emergency caesarean section ahead of schedule. Unfortunately, the baby died of a brain hemorrhage, despite the team’s efforts and blood transfusions. While looking for the causes of death, the doctors noticed that the mother’s blood contained strange antibodies. Therefore, she had a sample of her blood sent to specialists at a laboratory in Bristol.

The researchers then discovered that this blood was an extremely rare type, potentially incompatible with the baby’s blood. Therefore, the mother’s immune system could have produced antibodies against her baby’s blood, which unfortunately crossed the placental barrier. This is typical of a rare disorder called “hemolytic disease of the newborn” (or erythroblastosis fetalis), defined by the destruction of the infant’s red blood cells by antibodies from the mother. This woman’s blood was distinguished from her son’s by a particular protein present on the surface of the red blood cells.

Two rare forms, causing serious disease

The antigens that differentiate red blood cells are absolutely critical during a transfusion: if the blood is incompatible with the recipient’s, your immune system will immediately consider these antigens foreign to the body and attack them. This is why certain specialized researchers make an effort to carefully examine each blood sample considered “abnormal”; this is how a dozen new blood group systems have been discovered in the last decade.

Almost 40 years ago, a new antigen of high incidence, called Era, was discovered. However, the molecular basis of this antigen, as well as of the two other members of the Er blood group collection (Erb and Er3) discovered later, had not yet been elucidated.

The researchers were not only able to characterize the genetic background of these 3 antigens, but also identified two new antigens from the same “family”, called Er4 and Er5, which are extremely rare. These five antigens therefore make it possible to establish a completely new system of blood groups. ” Most people have what we consider to be the “normal” form of Er, but a small number of people have altered forms, including the new forms we have identified in this study. says Nicole Thornton of the NHSBT’s International Blood Group Reference Laboratory.

The recently discovered blood types Er4 and Er5 are rare but unfortunately cause cases of hemolytic disease of the newborn. Two patients, whose case was examined in the framework of this investigation, lost their babies for this reason.

Blood variations carried by a protein.

The team identified the Piezo1 protein, which plays an important role in many biological processes, as a carrier of this blood group system. Mutations in the PIEZO1 gene that codes for this protein are at the origin of the different antigens of the Er group (Era, Erb, Er3, Er4 and Er5). ” Confirmation of the role of Piezo1 as a carrier molecule for Er blood group antigens was demonstrated by immunoprecipitations, knockout studies, and CRISPR/Cas9-mediated gene expression in an erythroblast cell line. [ndlr : les érythroblastes sont de jeunes globules rouges] “, the researchers detail in the journal Blood.

These genetic variations result in the substitution of certain amino acids that make up the Piezo1 protein in a small number of people. Therefore, blood cells that contain the more common Piezo1 protein are considered foreign by your immune system. Therefore, there are currently five possible variations of the Piezo1 protein on the surface of red blood cells, which can lead to incompatibility.

But it could be that other genetic mutations linked to this rare blood remain to be discovered. An American team, from the New York Blood Center, is also interested in the Er blood group and has additional blood samples that appear to come from people with a rare Er group. Thanks to the UK team’s research, other variations may soon emerge.

In the meantime, this discovery will allow the development of new tests to identify people with rare blood types, with the goal of providing them with the best possible care. It will also make it possible to detect and treat as soon as possible (through an intrauterine blood transfusion) blood incompatibility problems between pregnant women and their babies.

The results of this study are likely to be used to formally define a new blood grouping system later this year, at a meeting of the International Society of Blood Transfusion.

Source: V. Karamatic et al., Blood

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