Predisposition to diseases in a person with zero blood group, what features are inherent in this type
At the beginning of the twentieth century, the Austrian scientist Karl Landsteiner observed that some people's erythrocytes are agglutinated by serum from others. He remembered the samples of agglutination and proved that the blood can be divided into groups. For the discovery of the AVO system, Landsteiner received the Nobel Prize.
- What is AVO system?
- Is there a zero blood group?
- Why does blood type zero occur?
What is AVO system?
Antigens of blood group AB0 are encoded by one genetic locus - AB0, which has three alternative (allelic) forms: A, B and 0. The child receives one of three alleles from each parent, which gives six possible genotypes and four types of blood cells (phenotype).
The discovery of ABO groups of red blood cells caused excitement among scientists. Until then, there were no data on the causes of severe reactions associated with donation. At the moment the procedure is absolutely safe and does not bear any risks. The human ABO blood type was used by lawyers, police in forensic medicine and anthropologists in the study of different population groups.
Antigens of the AB0 group in the blood are of paramount importance in transfusion medicine - they are the most immunogenic of all blood group compounds. Today, the most common cause of death from blood transfusion is a medical error.
However, despite the obvious clinical significance, the physiological functions of AB0 blood group antigens remain a mystery. People with a common type of blood 0 do not express either antigen A or B, and they are perfectly healthy. Numerous relationships have been identified between specific AB0 phenotypes and increased susceptibility to disease.
Is there a zero blood group?
Many people are wondering if there is a zero blood group? In Bombay, an interesting type of blood was found, which reacts to other groups in a strange way. Serum from this person contained antibodies that reacted with all red blood cells from normal phenotypes AB0 (groups 0, A, B and AB).
Named after the city in which it was first discovered, the "Bombay phenomenon" describes people who have no H. antigen on the surface of red blood cells. Since antigens A and B can not exist without the H antigen precursor, their erythrocytes also do not possess these substances. As a result, these individuals synthesize anti-H, anti-A and anti-B, and therefore they can only transfuse erythrocytes, which also do not have antigens H, A and B. Because of the rarity of this type of blood, the closest relatives usually act as donors.
Persons with a rare Bombay phenotype (hh) do not express the H antigen (also called substance H) that is present in the blood group of the blood 0. As a result, they can not synthesize an antigen A (called substance A) or a B antigen (substance B), regardless of which alleles they received in the process of inheritance. People with this type of erythrocytes are called "universal" donors - their biomaterial is suitable for all people..
Important! Transfusion of blood containing antigens AB or 0 leads to an acute immune reaction and rejection. This condition often ends in a fatal outcome. The most common synthesized immunoglobulins are IgM and IgG. They lead to hemolytic disease of the fetus (GPB)..
To avoid complications, it is necessary to diagnose the patient's blood type in a timely manner, because the usual tests show her as a group of 0. Anti-H-immunoglobulins are capable of provoking lethal hemolysis. This condition can not be prevented unless the laboratory technologist is aware of the existence of the Bombay blood group in the patient being examined. Bombay blood is considered very rare (5 people per million). Given the rarity of the Bombay group, not all patients are able to receive timely medical assistance.
Why does blood type zero occur?
Biosynthesis of antigens H, A and B includes a series of enzymes (glycosyltransferase) that transfer monosaccharides. The resulting antigens are oligosaccharide chains that are attached to lipids and proteins fixed in the erythrocyte membrane. The function of H-antigen, in addition to the intermediate substrate in the synthesis of agglutinogens of blood group AB0, is unknown, although it may be involved in cell adhesion. Zero blood group does not cause any serious illness in the person, since this is a variant of the norm. Deficiency of H antigen becomes a problem when blood transfusion is required.
The specificity of H-antigen is determined by the sequence of oligosaccharides. The minimum requirement for H-antigenicity is the terminal disaccharide "fucose-galactose where fucose has an alpha (1-2) bond. This antigen is produced by a specific fucosyltransferase that catalyzes the final stage of molecule synthesis.
Depending on the type of human blood, the antigen H is converted either into antigen A or B, or both. If a person has a group of erythrocytes of type 0, the antigen H remains unchanged. Thus, substance-H is present more in blood 0 and less in AB.
Two regions of the genome encode two enzymes with similar substrate features: FUT1, FUT2. Both genes are on chromosome 19 at q.13.3. It is worth noting that FUT1 and FUT2 are tightly connected to each other. Since these antigens are homologous, they probably resulted from the doubling of the gene of the common ancestor.
The locus of H contains four exons that span more than 8 kb of genomic DNA. The phenotypes of Bombay and para-Bombay are the result of point mutations in the FUT1 gene. At least one functional copy of FUT1 should be present (H / H or H / h) in H-antigen, which is synthesized on red blood cells. If both copies of FUT1 are inactive (h / h), then the result is Bombay blood.
The classical phenomenon of Bombay is due to the mutation of Tyr316Ter in the FUT1 coding region. As a result of the mutation, a stop codon is formed, leading to a truncated enzyme that does not have 50 amino acids at the C-terminus. This leads to the fact that the enzyme becomes inactive.
In Europeans, the phenomenon of Bombay can be caused by a number of mutations. Similarly, several mutations underlying the phenotype of para-bombay were reported. Se locus contains the FUT2 gene, which is expressed in the secretory glands. Violations in the expression of FUT2 also lead to a Bombay type of blood.
The Bombay phenotype is found in people who inherited two recessive alleles of the H (h / h) gene. These people do not synthesize H-carbohydrate, which is the precursor of antigens A and B. Because both parents should carry this recessive allele to pass this type of red blood cells to their children, this condition manifests itself more often in small closed communities. There is a high probability that both parents of the child have this type of blood.
Theoretically, the synthesis of anti-H-bodies during pregnancy can cause GPB. In practice, cases of GBP caused in this way are not described. Perhaps because of the rarity of the Bombay phenotype or because of the IgM produced by the mother's immune system. Because IgM is not transported through the placental blood vessels (eg, IgG), they can not reach the fetal blood flow to provoke the expected acute hemolytic reaction.
Advice! Incompatibility in people with a zero group occurs with a negative Rhesus factor in the mother and a positive in the fetus. Immune cells of the mother with zero group and negative Rh factor start to attack the red blood cells of the fetus. This discrepancy is most often the cause of the development of severe reactions caused by GPB. If such a condition arises, the doctor should evaluate the condition of the mother in order to make an effective treatment plan. If there is a rhesus incompatibility - it is necessary to inform the treating doctor about this without fail... ..