hh blood group

Hh antigen system - diagram showing the molecular structure of the ABO(H) antigen system

Individuals with the rare Bombay phenotype (hh) do not express substance H (the antigen that defines blood group O) on their red blood cells, and therefore do not agglutinate (bind with) A or B antigens of the ABO blood group system. Instead, they produce antibodies to H substance (which is present on all red cells except those of hh genotype) as well as to both A and B antigens, and are therefore compatible only with other hh donors.

Transfusion compatibility

Individuals with Bombay phenotype blood group can only be transfused with blood from other Bombay phenotype individuals. Given that this condition is very rare to begin with, any person with this blood group who needs an urgent blood transfusion will probably be unable to get it, as no blood bank would have any in stock. Those anticipating the need for blood transfusion (e.g. in scheduled surgery) may bank blood for their own use (i.e. an autologous blood donation), but this option is not available in cases of accidental injury.

Genetics

ABO - Bombay phenotype. It is easily explained by the H enzyme being coded for by a different gene to the A and B alleles.

Patients who test as type O may have the Bombay phenotype if they have inherited two recessive alleles of the H gene, (their blood group is O_h and their genotype is "hh"), and so do not produce the "H" carbohydrate (fucose) that is the precursor to the "A" and "B" antigens. It then no longer matters whether the A or B enzymes are present or not, as no A or B antigen can be produced since the precursor antigen is not present.

Despite the designation O, O_h negative is not a sub-group of any other group, not even O negative or O positive. When this blood group was first encountered, it was found not to be of either group A or B and so was thought to be of group O. But on further testing, it did not match even for O negative or O positive because of the absence of antigen 'H'. The H antigen is a precursor to the A and B antigens. For instance, the B allele must be present to produce the B enzyme that modifies the H antigen to become the B antigen. It is the same for the A allele. However, if only recessive alleles for the H antigen are inherited (hh), as in the case above, the H antigen will not be produced. Consequently, the A and B antigens also will not be produced. The result is an O phenotype by default since a lack of A and B antigens is the O type.

Because both parents that carry this recessive allele is required to transmit this blood type to their children, it almost goes without saying that the condition mainly occurs in small closed-off communities where the recessive gene has a chance to find two parents with this same blood type. Other examples may include noble families, which are inbred due to custom rather than local genetic variety.

The blood phenotype was first discovered in Bombay, now known as Mumbai, in India.

References in popular culture

Television: Yakitate Japan Episode 49 of Monoco Cup Arc — Reunion at the VIP Seat! Heaven Again! — the clown Pierrot has Bombay blood. He gets wounded in the course of the show, and being rare enough that according to the show only several hundred people in the world would have it. It turns out his father is the king of Monaco, who also has Bombay blood.

Television: Psi Factor The OSIR team encountered a young woman with the Bombay phenotype while working to solve the case of a haunting in the underground maintenance tunnels of a major city. The ghost would later be revealed as the spirit of her dead infant.

Television: Get Backers Episode 35 — Get Back the Life! — a little girl who has Bombay blood gets in a car accident and badly needs blood transfusions; the blood transfusions meant for her from a neighboring hospital were stolen by a shady organization for research purposes.

On General Hospital, Monica believed that her son, AJ Quartermaine, could not be her husband Alan's child and must have been the product of her affair with Rick, because AJ's blood type could not have arisen from hers and Alan's. It then turned out that Alan had the Bombay phenotype, and AJ really was his son.

The Harvard Medical School class of 2009 Second Year Show featured a Bollywood-style dance performance, with dancers representing blood cells inside the body of a character with Bombay-phenotype blood....

External links

• Hh at BGMUT Blood Group Antigen Gene Mutation Database at NCBI, NIH
• RMIT University The Bombay, para-Bombay and other H deficiencies