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The human body consists of various blood groups with one important one being the ABO blood group, which aids in blood transfusions. The ABO blood group was discovered during the years of 1900 and 1901 at the University of Vienna by Karl Landsteiner when he was trying to learn why some blood transfusions cause death and why some can save patients. There are four genotypes that are associated with the ABO blood group and they are the A blood type, the B blood type, the AB blood type, and the O blood type and along with that there are two antigens and two antibodies that are responsible for each ABO blood type. For example, the A blood type has the A antigen and the anti-B antibody, but doesn’t have the A antigen and the anti A antibody. The B blood type has the B antigen and the anti A antibody but not the A antigen or the anti A antibody. The AB blood type has both the A and B antigens but neither the anti A or B antibody and the O blood type has a combination of both anti A and B antibodies but neither the A or B antigen. These antigens and antibodies provide you with an advantage or disadvantage depending on where you are in the world and what disease you could and could not fight off. Selection of specific ABO blood groups can play a role in determining which diseases you are protected against and which diseases you are susceptible to.
The article The relationship between blood groups and disease written by David J Anstee shows how blood groups A, B, and O can present advantages and disadvantages depending on the type of disease that you are combating for example, the section Infectious Diseases and selection for ABO blood group antigens describes the role genes have in coding proteins to make that certain type of blood group for example, there is a gene that encodes a glycosyltransferase, which ends up transferring N-acetyl D-galactosamine (group A) or D-galactose (group B) to the nonreducing ends of glycans on glycoproteins and glycolipids (2-5). The O blood group forms from the inactivation of the A1 1 glycosyltransferase gene, and the nonreducing ends of the corresponding glycans, which expresses the blood group the H antigen. In addition to red blood cells ABH antigens are also expressed in body fluids and tissues and as stated the loss of a specific protein called A/B transferase can be harmful for patients who have the O blood type because it provides most of the functions that involve transferring lipids and proteins (4-12).
Another important disease that targets individuals who have the A, B, and AB rather than the O blood type is arterial and venous thromboembolism also known as VTE. Now, the real question is why this particular disease affects people of the A, B, and AB blood types and not people of the O blood type. Paragraph 2 states that individuals who don’t have the O blood type are at a higher risk for getting VTE because they have greater levels of two factors von Willebrand factor (vWF) and the VIII factor. A guess was made that the risk of developing VTE correlates directly to the levels of VIII and vWF factors because many patients who have the A2 blood group recorded lower levels of these types and proteins and the greater levels of these two factors are caused by the A, B, and H antigens being expressed on the N-glycans of vWF and that influences the half-life of the protein 10 hours for the O blood group and 25 hours for the non-O blood group (1-12). In this example having the A, B, or AB blood group would be a disadvantage while the O blood group would offer an advantage against arterial and venous thromboembolism.
Blood clot formation is another disease that has been studied because it has provided a survival advantage to individuals who have the O blood group. Mutation factors such as factor V Leiden and prothrombin 20210G>A provide an explanation to why they were found in early white humans from 20,000 to 24,000 years ago when it was the end of the ice age. Studies show that the V Leiden factor lowers the risk of hemorrhage (blood clots), other severe infections, and death during pregnancy (14-22). The article also states that the O blood group was a common blood group found in the world and the question that’s raised in my mind is that why was the O blood group so common throughout the world? Why wasn’t the A, B, and AB blood group as commonly found as the O blood group? What made the O blood group stand out and what did it have that the A, B, and AB blood group lacked? According to paragraph 3 the O blood group arose in Africa before the early migration of humans and it offers a selective advantage against malaria. An experimental support for this hypothesis was provided by Fry et al18 and by Rowe et al.19 and this report showed a reduction rosetting of Plasmodium falciparum isolates from group O Malian children compared with non-O blood groups. Parasitized red cells form rosettes with uninfected red cells and adhere to vascular endothelium, causing vasocclusion and severe disease (2-14). Based on this natural selection also had a role in the environment of Africa as the O blood group turned on survival genes against malaria to reduce its affect and avoid spreading to other red cells that blood groups A, B, and AB didn’t have.
There are other examples of infectious diseases that are linked to the ABO phenotype such as Cholera and Smallpox. Cholera is a type of infection caused by ingestion of food or water contaminated with the bacterium Vibrio cholerae (World Health Organization 1-2) and according to the World Health Organization it is responsible for 21,000 to 143,000 deaths worldwide. So, why is this the case and which blood group was responsible for causing cholera and why? According to paragraph 4 of Infectious Diseases and selection for ABO blood group antigens the O blood group phenotype has a greater chance of being prone to severe infections as compared to the non-O blood group phenotypes. There is a low presence of Blood group O and more presence of blood group B in the Ganges Delta in Bangladesh and that is correlated directly to the selective pressure that cholera brings. This shows that the O allele is fixed in populations of Asia and the B allele drifted off because the O allele offered a survival advantage in this case to Cholera. Forces such as Genetic Drift and the founder effect also explain why the allele frequencies of blood groups change for example, lines 6-18 of the fifth paragraph describes the high frequency of the HIV-1 resistance mutation CCR532 in Europe with protection against Smallpox and the Black Death. However, the mutation change from the A allele to the O allele and the CCR532 mutation happened earlier in human evolution before Smallpox and the plaque played a part during medieval times. Now, this A to O mutation change could have arose due to malaria being present in Africa before early humans migrated to Europe and the migration of early humans into Europe can also explain why allele frequencies are different in parts of the world.
ABO blood groups and what each individual carries can also depend on various pathogens that influence it, for example in the article Pathogen-Driven Selection in the Human Genome written by Rachele Cagliani and Manuela Sironi the section under A Wide Spectrum of Selection Targets talks about the expression of the ABO histo-blood group antigens on the gastrointestinal mucosa and in bodily secretions relies on an action of a fucosyltransferase, which is encoded by FUT2, a gene part of the Lewis blood group system. Both the ABO and FUT2 have similar historical polymorphisms and a long-lasting pressure that is spread worldwide due to selective pressure and infectious agents. For example, some pathogens such as Plasmodium falciparum, Norwalk virus, Campylobacter jejuni, Helicobacter pylori, and Vibrio cholerae is controlled by the ABO blood group and its associated secretor status. In many cases the vulnerability to a disease or the symptoms of that particular disease as Rachele explains it is due to the fact that ABO antigens are used by attachment sites by specific pathogen- encoded molecules, which in turn are subjected to a selective pressure for increased ability to infect their host as demonstrated with the H. pylori babA gene that encodes the adhesin responsible for the ABO antigen binding. The function of ABO antigens as pathogen receptors is also thought to be the reason why other genes that are responsible for producing the blood group phenotypes have been targeted by pathogen-driven selection in humans (Rachel/Manuela, 2013). This shows how different blood groups are selected to fight off different kinds of pathogens.
Natural selection is one force of evolution that plays a part in determining which blood group you would have in any part of the world where a specific disease or diseases are present. The article Natural Selection and infectious disease in human populations written by Elinor K. Karlsson, Dominic P. Kwiatkowski, and Pardis C. Sabeti under the Signatures of negative selection and purifying selection section in lines 1-9 states “Negative selection eliminates existing detrimental variation from a population. For example, when human populations in the Ganges River Delta encountered pathogenic Vibrio cholerae, individuals of blood type O had higher risk of dying from severe cholera, which put them at a strong reproductive disadvantage. Nowadays, populations in the cholera-endemic Ganges River Delta have the lowest rates of blood type O in the world, which is consistent with negative selection. Purifying selection is the ongoing removal of deleterious alleles as they arise. Signatures of purifying selection include decreased overall diversity, loss of functional variation and an excess of rare alleles. Purifying selection also manifests as a lack of substitutions between species, and this signal is used to identify functionally important, highly conserved genomic regions in cross-species comparisons (Elinor/Dominic/Pardis, 2014).” In this example in the region of Bangladesh the O blood type is considered a negative selection because it had been the cause of many people dying from the disease cholera and now blood group O is rarely seen at that region. Both natural selection and purifying selection played a role in helping get rid of the alleles that make up the O blood group because it offered a disadvantage and wasn’t a survival advantage to people living in the cholera regions of the Ganges River Delta.
As mentioned before in the paper there are two things secretors and non-secretors that relate to the ABO blood group and have roles to play. Now, the real question to ask is what are these secretors and non-secretors, what do they do and what effect does it have on the ABO blood group? According to the article Importance of Secretor Status written by Dr. Peter J. D’ Adamo the gene coding for your blood type lies on chromosome 9q34, but a separate gene called FUT2 interacts with your blood type gene, and determines your ability to secrete your blood type antigens into blood fluids and tissues. A person can be either a secretor or a non-secretor and it doesn’t matter whether you’re an A, B, AB, or O blood type, for example a person can be an A secretor, an A non-secretor, a B secretor, a B non-secretor, an O secretor, or an O non-secretor. Dr. Peter defines a secretor and non-secretor as “A secretor is defined as a person who secretes their blood type antigens into body fluids and secretions like the saliva in your mouth, the mucus in your digestive tract and respiratory cavities, etc. Basically, what this means is that a secretor puts their blood type into these body fluids. A non-secretor on the other hand puts little to none of their blood type into these same fluids. As a general rule, in the U.S. about 20% of the population are non-secretors and the remaining 80% being secretors.” (Dr. Peter, 6-8) These secretors and non-secretors come with advantages and disadvantages on the ABO blood groups for example, according to Dr. Peter “Being a non-secretor comes with a health disadvantage because you are unable to secrete blood type into your saliva, mucus, etc. and that allows for an added protection against the environment, particularly with respect to microorganisms and lectins and as a secretor in addition to the protection against the environment it also promotes a stabilized blood type friendly intestinal bacterial ecosystem. Many of the friendly bacteria in your digestive system uses your blood type as one of their preferential foods. Since secretors have a steady supply of blood type in the mucus that lines the digestive tract; their bacteria have a much more constant food supply.” (Dr. Peter, 9-15) Based on this it’s better to be a secretor as it comes with many advantages that can also help the good bacteria inside you.
Secretors and non-secretors come with advantages and disadvantages, now what’s the difference between both of them? Under the section Metabolic Differences between Secretors and non-secretor’s lines 1-13 state “Similar to the ABO blood groups, additional genetic information must be linked to the secretor gene, because predictable trends in non-blood type aspects of physiology have a close association with secretor/non-secretor status. Aspects of physiology such as the relative activity of an enzyme called intestinal alkaline phosphatase; propensities toward clotting, reliability of some tumor markers, and general performance of your immune system have predictable trends depending on your secretor status.” “The activity of intestinal and serum alkaline phosphatase is correlated with secretor phenotypes. Non-secretors, regardless of the ABO blood groups have lower alkaline phosphatase activity. Blood type has an impact on clotting ability to a certain extent. Studies show that 30% of the genetically determined variance in plasma concentration of the vWf (von Willebrand factor) has a direct relationship to the ABO blood type. Blood group O individuals have the lowest amount of this clotting factor.” “Secretors have slow clotting while non-secretors have short bleeding times and higher levels of the clotting factors VIII and vWf. ABO and secretor genetics interact together to influence blood viscosity and what this means is that an A non-secretor will be at the further end of the spectrum with the slowest bleeding times, thickest blood viscosity, and more probability to have high platelet aggregation. The other end of the continuum will contain the O secretors, who will have the longest bleeding time, thinnest blood, and less prone to having platelet aggregation, which means that the A non-secretors will be very vulnerable to future atherothrombotic and heart disease (Dr. Peter, 1-13). Overall based on all this information it’s important to be a secretor as it provides you with many advantages and being protective against various diseases, however, if you are a non-secretor then you’ll be exposed to various diseases some that might be deadly.
ABO blood groups in the human body are continuously going through research and a lot of factors play a part in which blood group phenotypes you’ll inherit. There are various antigens that are associated with the ABO blood groups and pathogens that can be the direct cause of which blood groups get expressed and which diseases it’ll be capable of fighting off. Blood groups have been evolving from the early humans to today and forces of evolution such as natural selection, genetic drift, and the founder effect can explain why particular blood groups exist in specific regions and why the alleles are becoming fixed over time.
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