Bombay phenotype

Bombay phenotype is a rare genetic variation found in the ABO blood group system where individuals do not express the H antigen, which is a precursor to the A and B antigens. This condition is named after the city of Bombay (now Mumbai), India, where it was first discovered. The absence of the H antigen means that individuals with the Bombay phenotype can only receive blood from other individuals with the same phenotype, making blood transfusions particularly challenging for those affected.

Genetics

The Bombay phenotype (hh) results from a homozygous mutation in the FUT1 gene, which encodes the enzyme fucosyltransferase 1, responsible for the synthesis of the H antigen. In the absence of functional fucosyltransferase 1, the H antigen cannot be produced, and consequently, the A and B antigens, which are modifications of the H antigen, also cannot be expressed. This genetic condition is inherited in an autosomal recessive manner, meaning an individual must inherit two copies of the mutated gene, one from each parent, to exhibit the phenotype.

Clinical Significance

The primary clinical significance of the Bombay phenotype lies in blood transfusion and organ transplantation. Individuals with this phenotype can only receive blood from donors with the same phenotype, as they have anti-H antibodies that will react with any blood containing the H antigen, which is present in all other ABO blood types. This makes finding compatible blood donors extremely challenging. In addition, the Bombay phenotype can complicate ABO typing, leading to potential misclassification if not correctly identified.

Prevalence

The Bombay phenotype is extremely rare, with a higher prevalence in certain populations, particularly in South Asia. Despite its rarity, awareness and accurate identification of this phenotype are crucial for the safe administration of blood and blood products.

Diagnosis

Diagnosis of the Bombay phenotype is typically made through blood typing tests that include specific testing for the H antigen and anti-H antibodies. Molecular genetic testing can also identify mutations in the FUT1 gene, confirming the diagnosis.

Management

Management of individuals with the Bombay phenotype primarily involves awareness and preparedness, especially in the context of medical procedures requiring blood transfusion. It is essential for these individuals to carry medical alert information and for healthcare providers to have access to appropriately matched blood products.

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