Bombay blood group.
RAREST BLOOD GROUP. ONLY ONE PERSON OUT OF 7600 HAS THIS GROUP.
This is an extremely rare ABO group, called so because it was first discovered
among some people in Bombay (now Mumbai). Although the group is more likely to
occur in East Indians, it is a very rare group even here. It is not restricted
to East Indians but found in Caucasians, Japanese, etc. Their red cells lack ABH
antigens and their sera contain anti-A and anti-B and anti-H. The anti-H would
not be detected in the ABO group but would be detectable in pretransfusion
tests.
The Bombay blood group is a rare group except in parts of India where a
frequency of 1 in 7,600 has been observed. A high level of consanguinity has
been observed among the parents of the Bombay phenotype(8). Individuals with the
Bombay phenotype fail to express ANY A, B, or H antigen on their red cells or
other tissues (8,39).
The cause of this antigenic absence is that the individuals produce no H
glycosyl transferase ( FUT1). There is no H enzyme activity detected on the
individuals red cells or in their serum.
These individuals may, however, posses either the A and / or the B gene on
chromosome 9 and while an A or B glycosyl transferase may be produced there is
no H antigen precursor that can be converted into either the A or B antigen (8,
39).
The cause of the Bombay phenotype is , predominately, mutation in the H gene on
chromosome 19 that causes a non functional H glycosyl transferase to be
produced. This is generally a Mendelian recessive gene. One cause identified has
been a mutation that changes the code for trypsin at amino acid residue 316 of
the transferase to that for a stop codon. The result is a truncated, non
functional H transferase (8).
Generally ABO group of blood will have their own specific antigens and
antibodies in their blood. All the blood groups in this category will have
antigen H in common in addition to their own specific antigens and antibodies.
But Bombay blood group doesn't include any antigens in its blood and it have
antibodies H, A and B in its blood. If ABO category(A, B, AB and O) group of
blood is given to Bombay blood group patients due incompatibility the antigens
of the donors blood will react with antibodies of the patient leading to the
death of cells and ultimately to the death of the patient.