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- Blood by genes: how the discovery of a new donor system will save lives
Blood by genes: how the discovery of a new donor system will save lives
Even if the blood type and Rh factor match, transfusion can sometimes be dangerous. Scientists at the University of Bristol have figured out how to identify a rare hereditary trait that makes it difficult for patients to find a suitable donor. The results of the study in the future will help to more accurately select blood for transfusion and reduce the risk of complications, the Federal State Budgetary Institution "NMITS of Hematology" of the Russian Ministry of Health told Izvestia. How the discovery will change medical practice and what other innovations there are in this area can be found in the Izvestia article.
How scientists learned to identify rare blood features
Scientists from the University of Bristol and the British blood service NHS Blood and Transplant have figured out how to identify one of the rarest hereditary features of human blood. The results of the study, published in the scientific journal Blood, will in the future make it possible to find people in advance who may need a special selection of donors and reduce the risk of dangerous complications during transfusion.
Usually, when selecting donated blood, its group and Rh factor are taken into account. However, there are hundreds of other distinguishing features on the surface of red blood cells — red blood cells — that also affect compatibility. In most people, they match, but there are extremely rare features that make it much more difficult to find a suitable donor.
The researchers focused on one such trait, which is present in more than 99.9% of the world's population. Its absence is extremely rare and, in certain circumstances, can cause a dangerous immune reaction during transfusion. Until recently, doctors could detect this feature with the help of special laboratory tests, but they did not know which hereditary changes underlie it.
Now scientists have managed to determine the genetic cause. This opens up opportunities for the development of special tests that will help identify people with this feature in advance and look for donors whose red blood cells may be suitable for them. In the future, the data obtained can be used to form databases of rare donors, so that in emergency situations you do not waste time on a long search.
Olesya Pshenichnikova, PhD, Head of the Laboratory of Genetic Engineering at the National Research Medical Center of Hematology of the Russian Ministry of Health, told Izvestia that the establishment of the genetic basis of this feature was an important achievement, primarily for the diagnosis of rare cases of incompatibility. We are talking about the AnWj antigen, a special feature on the surface of red blood cells, which was first discovered back in 1972. Scientists have established that its hereditary absence is associated with the loss of a region of the MAL gene.
— Many differences between blood groups are associated with the replacement of one "letter" in DNA — such changes are well detected by standard methods of genetic research. In this case, people with the hereditary absence of AnWj have lost an entire section of the MAL gene. Such a deletion is like a missing piece of text, not a typo in one word," the specialist said.
Why else would a suitable blood type be dangerous?
Matching blood type and Rh factor does not always guarantee that a transfusion will take place without complications. In addition to these characteristics, red blood cells have many other features that the human immune system can recognize as foreign.
If a patient is transfused with red blood cells with an antigen unfamiliar to his body, the immune system in some cases begins to produce antibodies against him — special proteins designed to recognize foreign substances. In subsequent transfusions, such antibodies can attack donor cells and cause their destruction.
This problem becomes the most serious for people with rare blood disorders. For example, a patient who lacks the AnWj antigen discovered by scientists may develop antibodies against it. If such a person is transfused with red blood cells containing this antigen, there is a risk of a dangerous reaction.
Doctors call this complication a hemolytic transfusion reaction. During its development, donor red blood cells are destroyed, which in severe cases can lead to serious disorders of the body.
According to Evgeny Zhiburt, MD, Professor, Head of the Department of Transfusiology and Blood Transfusion at the N.I. Pirogov National Medical Center, the establishment of the genetic basis of a rare antigen will make it possible to more purposefully prevent the destruction of donor red blood cells during transfusion and combat such complications.
Olesya Pshenichnikova said that similar complications have already been described in the medical literature. However, the presence of antibodies does not mean that a dangerous reaction will necessarily occur with every transfusion.
— It is not yet known how often hemolysis occurs: there are too few published observations for a reliable assessment. Therefore, the presence of these antibodies may require a special selection of donor red blood cells," she said.
The main difficulty lies in finding a suitable donor. Since the AnWj antigen is present in almost all people, it is extremely difficult to find a person who does not have it. In this case, a patient with the appropriate antibodies may need just such donor red blood cells.
How genetic tests will help find rare donors
One of the main practical results of the study may be the development of new methods of blood genotyping. Since scientists were able to establish a link between the hereditary absence of AnWj and changes in the MAL gene, it became possible to purposefully search for people with similar features.
Genetic tests will potentially make it possible to identify rare donors in advance, whose red blood cells may be suitable for patients with antibodies against AnWj. The information obtained can be used in the formation of specialized registers and the creation of stocks of compatible blood components.
However, genotyping is not a universal way to determine compatibility. In some cases, the AnWj antigen ceases to be detected on the surface of red blood cells not due to a hereditary change, but against the background of certain diseases. Therefore, genetic analysis is not always able to explain its absence.
In addition, a test focused on a specific gene change may not reveal other, as yet unknown, reasons for the absence of the antigen.
— In practice, it is most useful to combine serology, genotyping and accounting for rare donors. The genotype helps to identify candidates in advance, but the final selection should take into account the remaining antigens, the identified antibodies and the results of the compatibility study," Pshenichnikova emphasized.
In Russia, the study of the antigenic profile of donors is already going beyond the definition of the usual blood groups. According to current regulatory requirements, in addition to the ABO system, the main antigens of the rhesus system, as well as the K antigen of the Kell system, are determined.
As Evgeny Zhiburt explained, the examination of donors in the Russian Federation is carried out at a modern level in accordance with the order of the Ministry of Health No. 1166n of 2020. At the same time, the concept of "rare blood group systems" is not specified separately in Russian regulatory documents.
Some blood service facilities and specialized medical centers provide advanced typing using other systems, including Kidd, Duffy, MNS, Lutheran, and Lewis. Such studies help to assess the prevalence of various antigenic combinations and create databases of donors.
Some large medical centers already have registries of people with an extended antigenic profile, including rare phenotypes. In addition, special stocks of frozen erythrocyte components are being formed, which can be used for complex blood selection.
Could the discovery help identify other diseases?
In addition to improving the safety of transfusions, the study of the MAL system is of interest for the diagnosis of certain blood diseases. The researchers found that the absence of the AnWj antigen can have both hereditary and acquired origin.
In particular, its expression can decrease or disappear against the background of certain hematological and oncological diseases. At the same time, the MAL gene itself can remain unchanged, despite the absence of the corresponding antigen on the surface of red blood cells.
This difference opens up opportunities for further study of the mechanisms by which diseases affect the properties of blood cells. However, experts warn that the absence of AnWj cannot be used as an independent diagnostic feature yet.
— The absence of AnWj by itself does not indicate a specific disease. So far, this feature cannot be used to make a diagnosis, assess the severity of the disease, or monitor treatment," Pshenichnikova said.
According to experts, studying the MAL gene may help to better understand why the properties of red blood cells change in certain diseases. However, additional studies are needed to determine the diagnostic value of the antigen.
In particular, scientists will have to determine how often changes in AnWj expression occur in various pathological conditions and whether they can be linked to specific mechanisms of disease development.
How will blood transfusion change in the next 5-10 years
In the long term, studies of rare blood group systems can contribute to the development of personalized transfusiology. We are talking about a more detailed determination of the antigenic characteristics of donors and patients, which will allow us to take into account significantly more compatibility factors than in a standard study.
Olesya Pshenichnikova noted that molecular typing for several blood group systems is already used in medical practice. Its main task is not to find a donor with a completely identical genetic profile, but to select red blood cells that will not cause a reaction from the patient's existing antibodies and, if possible, reduce the risk of new ones.
The extended study may be especially useful for patients who require multiple transfusions, people with antibodies to several red blood cell antigens, as well as patients with rare variants of rhesus antigens.
The discovery of MAL allows you to add another indicator to such an analysis. In the future, this may contribute to the formation of more detailed donor databases and speed up the search for compatible blood.
According to Evgeny Zhiburt, the development of such research can indeed lead to the creation of expanded genetic profiles of donors and patients. This approach will be especially important for people with congenital anemia and patients who require multiple blood transfusions.
However, the massive introduction of genotyping is associated with financial, technical, and organizational constraints. In addition to the cost of the research itself, special equipment, trained specialists and proven methods of processing genetic data are needed.
According to experts, a gradual expansion of genotyping looks realistic in the next 5-10 years, primarily in large medical centers and for patients in need of complex blood selection.
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