BRIEF NOTES ON BOMBAY BLOOD GROUP

Bombay blood group is the rarest blood group and is reported in Bombay (Mumbai) in India.This blood group phenotype was first discovered by the Doctor YM Bhende in 1952. It is reported to occur in 1 out of every 250,000 people.In parts of India the incidence has been observed to be as much as 1 in every 7,600 people.

 Bombayblood group is also called the HH group. The special feature of this group is that they do not express the H antigen. H antigen act as a precursor to each of the ABO blood group antigens, apparently present in all people except those with the Bombay Blood phenotype. As a result they cannot form A antigens or B antigens on their red blood cells. Thus they can donate blood to anybody with ABO grouping but can receive blood only from Bombay blood group people.

In a person with blood group A, antigen of type 'A' and antibody of type 'B' is present in his/her blood. People with B have antigenB and antibody B in their blood. People with AB have both antigen A and B in their blood and no antibodies. People with O blood group have only antibodies A and B and no antigens.All these groups have an antigen H in the blood as well. There are very few people who do not have this antigen H in their blood. Instead they have antibody H because of which no other blood can be given to them
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Blood Groups  (Antigens and Antibodies)

Blood Group           Antigens              Antibodies

A                                 A,H                        B

B                                  B,H                       A

AB                              A,B,H                    Nil

O                                   H                        A,B

Bombay Blood Group   Nil                    A,B,H

                        Antigens A and B of A, B and O blood phenotype are synthesized from a precursor mucopolysaccharide in the presence of the dominant allele of another pair designated as H and h. With genotypes HH or Hh the precursor is converted to an H antigen which, in turn, in the presence of I^A and/or I^B allele is partly converted to antigen A and/or antigen B. Gene h is termed amorph because it is producing no visible product. When the  genotype of a person is HH or Hh, A persons of group A produce antigens A andH, group B persons produce antigens B and H, and group AB persons produce antigens A, B and H. Group O persons produce only antigen H if they are of the genotype ii

The H gene appears to be necessary for the formation of A and B antigens It is very common 99.9% of all individuals have an HH or Hh genotype.The allele h is very rare and does not produce the L-Fucose transferase necessary for formation of the H-Structure.The genotype (hh) is extremely rare and is known as the Bombay Phenotype