Researchers identify new blood types

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If the ABO and Rhesus systems are the most well-known (and used) blood group classification systems, you should know that there are actually dozens of ways to group red blood cells based on the molecules (sugars, proteins) they carry on their surface 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 so far.

Unfortunately, sad circumstances led to this discovery. An unborn child was showing signs of stress so the medical team at the UK hospital where the mother was taken decided to perform an emergency C-section before the baby was due. Unfortunately, the baby died of a brain hemorrhage, despite the team’s best efforts and blood transfusions performed. While looking for the causes of death, doctors noticed that the mother’s blood contained strange antibodies. A sample of his blood was therefore sent to specialists at a laboratory in Bristol.

The researchers then discovered that this blood was of an extremely rare type and may not have been compatible with the baby’s blood. So the mother’s immune system could have made antibodies against her baby’s blood, which unfortunately has crossed the placenta. This is typical of a rare condition called ‘haemolytic disease of the newborn’ (or erythroblastosis fetalis), which is defined by the destruction of the child’s red blood cells by the mother’s antibodies. This woman’s blood differed from that of her child because of a specific protein present on the surface of red blood cells.

Two rare forms that cause serious illness

The antigens that differentiate the red blood cells are crucial in a transfusion: If the blood is not compatible with that of the recipient, his immune system will immediately classify these antigens as foreign and attack them. For this reason, certain specialized researchers strive to carefully examine any blood sample classified as “abnormal”; In this way, a dozen new blood group systems have been discovered in the past decade.

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

Not only were the researchers able to characterize the genetic background of these 3 antigens, but they also identified two new antigens from the same “family”, namely Er4 and Er5, which are extremely rare. These five antigens thus enable the establishment of a completely new blood group system. ” Most people have what we consider to be the “normal” form of Er, but a small number of individuals have altered forms, including the new forms we identified in this study says Nicole Thornton of the NHSBT International Blood Group Reference Laboratory.

The recently discovered blood types Er4 and Er5 are uncommon but unfortunately cause cases of hemolytic disease in the newborn. Two patients whose case was studied in this research lost their babies because of this.

Blood variations carried by a protein

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

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

But it could be that other genetic mutations linked to this rare blood have yet 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 be 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 enable the development of new tests to identify people with unusual blood types, with the aim of providing them with the best possible care. It will also be possible to detect and treat blood incompatibility problems between pregnant women and their babies as early as possible (via a blood transfusion in the womb).

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

Source: V. Karamatic et al., Blood

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