Bombay Blood Group

                                        
                             Bombay Blood Group

  It is called the HH group, the peculiarity is that they do not express the H antigen. 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. Bombay blood group is a rare blood type. This blood phenotype was first discovered in Bombay, now knows as Mumbai. Dr. Y. M. Bhende in 1952. It is mostly found in India, Pakistan, and Iran. 

  The first person found to have the Bombay phenotype had an interesting blood type that reacted to other blood types in a way never seen before. The serum contained antibodies that reacted with all red blood cells normal ABO phenotypes. The red blood cells appeared to lack all of the ABO blood group antigens and to have an additional antigen that was previously unknown.

   Individuals with the rare Bombay phenotype (hh) do not express H antigen (also called substance H), the antigen which is present in blood group O. As a result, they cannot make A antigen  (also called substance A) or B antigen (substance B) on their red blood cells, whatever alleles they may have of the A and B blood-group genes, because A antigen and B antigen are made from H antigen. For this reason people who have Bombay phenotype can donate red blood cells to any member of the ABO blood group system (unless some other blood factor gene, such as Rh, is incompatible), but they cannot receive blood from any member of the ABO blood group system (which always contains one or more of A, B or H antigens), but only from other people who have Bombay phenotype.

Incidence:

   
This very rare phenotype is generally present in about 0.0004% (about 4 per million) of the human population, though in some places such as Mumbai (formerly Bombay) locals can have occurrences in as much as 0.01% (1 in 10,000) of inhabitants. Given that this condition is very rare, 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 may bank blood for their own use, but of course, this option is not available in cases of accidental injury. For example, by 2017 only one Colombian person was known to have this phenotype, and blood had to be imported from Brazil for a transfusion.

Genetics: 

 Bombay phenotype occurs in individuals who have inherited two recessive alleles of the H gene (i.e.: their genotype is hh). These individuals do not produce the H carbohydrate that is the precursor to the A and B antigens, meaning that individuals may possess alleles for either or both of the A and B alleles without being able to express them. Because both parents must carry this recessive allele to transmit this blood type to their children, the condition mainly occurs in small closed-off communities where there is a good chance of both parents of a child either being of Bombay type or being heterozygous for the h allele and so carrying the Bombay characteristic as recessive. Other examples may include noble families, which are inbred due to custom rather than local genetic variety. 

Hemolytic Disease of the Newborn:

 In theory, the maternal production of anti-H during pregnancy might cause hemolytic disease in a fetus who did not inherit the mother's Bombay phenotype. In practice, cases of HDN caused in this way have not been described. This may be possible due to the rarity of the Bombay phenotype but also because of the IgM produced by the immune system of the mother. Since IgMs are not transported across the microscopic placental blood vessels (like IgG are) they cannot reach the bloodstream of the fetus to provoke the expected acute hemolytic reaction.

what is Bombay(Mumbai) Blood group?

 To understand Bombay blood group we must understand the details of blood grouping. When we say someone has blood group A, it means that the person has antigen of type A and antibody of type B in blood. People with AB have both antigen A & B in their blood and no antigens. However what is not generally known is that 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.