This rare ABO-related phenotype is described as being an “H-deficient secretor.” Those with Para-Bombay cannot make H antigen on their red blood cells (and can’t make RBC-bound A or B antigen), but unlike those with the “Bombay Phenotype,” they CAN make H antigen (and thus, A or B antigen) in their secretions and plasma. Genetically, this means that Para-Bombays lack an active H allele (their genotype is hh) but carry at least one Se (“secretor”) allele. Para-Bombays may make a small amount of A or B antigen (depending on their ABO genotype) and H antigen in their plasma, some of which may attach to the RBC surface. Despite this, Para-Bombay individuals may make a strong antibody against the H antigen (just like those with Bombay Phenotype); as a result, they may require H-negative blood for transfusion.
See the Bombay video for more information.
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