“UNLOCKING THE MYSTERY OF THE BOMBAY BLOOD GROUP: EMBRACE YOUR UNIQUE IDENTITY”

 

In 1952, Dr. YM Bhende described a new blood group that is now called the "Bombay Phenotype". Persons with the normal blood group carry the H antigen, which serves as a precursor for red blood cells; on the other side, people with the Bombay phenotype lack the H antigen, and their serum contains anti-H bodies. According to Watson and Morgan's theory, the Bombay phenotype is a rare homozygous hh, and the H antigen may be the result of a gene independent of the A-B-O systems. Ceppellini hypothesized that this blood type is caused by a homozygous recessive gene that prevents the production of the A, B, and H antigens [1, 2].

 

Inheritance And Genetics

The ABO blood group system is directly related to the genetics and heredity of the Bombay phenotype. The presence or lack of particular antigens (carbohydrates) on the surface of red blood cells determines the ABO blood group [3]. Enzymes combine particular sugars with a precursor antigen called the H antigen to create the A and B antigens [2]. Mutations in the FUT1 gene, which codes for the enzyme required to add fucose (another sugar) to the H antigen, prevent people with the Bombay phenotype from producing the H antigen [5]. The FUT1 gene has an autosomal recessive inheritance pattern and is found on chromosome 19 [2]. To have the Bombay phenotype, a person must inherit two copies of the mutant FUT1 gene, one from each parent. One copy of the mutant FUT1 gene is inherited by individuals who have the Bombay phenotype and can be passed on to their progeny. There is a 25% chance that a child with two copies of the mutant FUT1 gene and the Bombay phenotype will inherit both copies from parents who are Bombay phenotype carriers. A 25% possibility exists that the child will inherit two normal FUT1 genes and not be impacted by the disorder, and a 50% chance exists that the child will be a carrier like their parents [1, 4, 6].

 

For those who are Bombay phenotype carriers and want to start a family, genetic guidance is frequently advised. It's important to understand that the Bombay phenotype and the ABO blood group inheritance are independent of one another. The O allele is recessive to both the A and B alleles and these alleles are codominant in the autosomal dominant pattern of inheritance for the ABO blood group. As a result, a person's parents may have given them an ABO blood type that is different from their FUT1 genotype. For instance, a parent who has the Bombay phenotype and has the ABO blood type O can pass it on to their child who carries the A or B blood type allele from the other parent. Mutations in the FUT1 gene, which codes for the enzyme required to add fucose to the H antigen on the surface of red blood cells, influence the inheritance pattern and genetics of the Bombay phenotype. The ABO blood group system, which has an autosomal dominant inheritance pattern, is unrelated to the Bombay phenotype, which has an autosomal recessive pattern of heredity.

Transfusion Compatibility

Bombay blood group members can give to all ABO blood group members and can only receive from Bombay blood group members. An IgM antibody called Bombay anti-H can bind complement and destroy red blood cells. Bombay blood is incompatible with all ABO donors because the H antigen is present in all ABO blood groups. Given the rarity of this illness, anyone with this blood group who requires an urgent blood transfusion is likely to be turned away because no blood bank would have any stock available. Autologous blood donation is a possibility for those who anticipate needing a blood transfusion (such as after scheduled surgery), but it is not available in the event of an accident [6]. People with the Bombay blood group may not be identified if the right blood grouping or testing procedures are not used. This group would be classified as the O group because, like the typical O group, it would not react to anti-A and anti-B antibodies. A crossmatch with the O group would reveal any incompatibility or cross-reactivity. To identify this group, reverse grouping or serum grouping must be used. People with the Bombay phenotype frequently experience difficulty during emergency scenarios and procedures requiring blood transfusions because of the rarity of this blood type. It's possible that blood units with appropriate phenotypes are not always available in standard blood banks. It is essential for people with the Bombay phenotype to carry a medical alert card or wear a medical alert bracelet that displays their specific blood type. This makes it possible for medical professionals to respond appropriately to emergencies [4].

 

The Bombay blood group must be identified through reverse grouping or serum grouping. With two recessive alleles of the H gene, patients who test as type O may have the Bombay phenotype (their blood group is Oh and their genotype is "hh") because they lack the "H" carbohydrate (fucose), which serves as the precursor to the "A" and "B" antigens. The presence or absence of the A or B enzymes is then irrelevant because the absence of the precursor antigen H prevents the production of any A or B antigens. As a result, these people were genetically referred to as having the Bombay phenotype or homozygous hh [4].

Conclusion

A mutation in the FUT1 gene results in the absence of the H antigen on red blood cells, giving rise to the uncommon blood type known as the "Bombay phenotype." This trait is autosomal recessive, which means that for a child to have the Bombay phenotype, both parents must have the mutant FUT1 gene. The presence of anti-H antibodies in the person's serum identifies them as having the Bombay phenotype, which is distinct from the ABO blood group system. Accordingly, those who have the Bombay phenotype can give blood to all ABO blood groups but can only accept blood from others who also have the phenotype. Due to the Bombay phenotype's rarity, people with this blood group might face difficulties when receiving blood transfusions because most blood banks do not keep a ready supply of this blood type on hand. To ensure a proper emergency response, it is crucial for people with the Bombay phenotype to carry a medical alert card or wear a medical alert bracelet. In addition, genetic counselling is advised for Bombay phenotype carriers who want to start a family. In terms of genetic inheritance and transfusion compatibility, the Bombay phenotype is a distinct blood group that needs specific consideration.

 By: Anas Iqbal

References

 

1)      Yunis, E. J., Svardal, J. M., & Bridges, R. A. (1969). Genetics of the Bombay phenotype. Blood, 33(1), 124-132

2)      Kaneko, M., Nishihara, S., Shinya, N., Kudo, T., Iwasaki, H., Seno, T., ... & Narimatsu, H. (1997). Wide variety of point mutations in the H gene of Bombay and para-Bombay individuals that inactivate H enzyme. Blood, The Journal of the American Society of Hematology, 90(2), 839-849

3)      Khan, M. Q. (2009). Bombay blood group: A case report. Pac J Sci Technol, 10, 333-7.

4)      POURAZAR, A., Joshi, S., Clarke, V. A., & Ala, F. (2004). Another case of Para-Bombay phenotype in an Iranian donor

5)      Chowdhury, F. S., Siddiqui, M. A. E., Rahman, K. G. M., Nasreen, Z., & Begum, H. A. (2011). A rare and clinically important blood Group-Bombay blood group. Bangladesh Journal of Medicine, 22(1), 21-23.