Bombay Blood Group - Oh

Source:  Bombay Blood Group - Oh    Tag:  bombay phenotype
The h/h  blood group , also known as Oh or the  Bombay blood group , is a rare  blood type
This  blood  phenotype was first discovered in  Bombay , now known as Mumbai, in India, by Dr. Y. M. Bhende in 1952.

The Hh blood group contains one antigen, the H antigen, which is found on virtually all RBCs and is the building block for the production of the other antigens within the ABO blood group.
H antigen deficiency is known as the "Bombay phenotype" (h/h, also known as Oh) and is found in      1 of 10,000 individuals in India and 1 in a million people in Europe. There is no ill effect with being H deficient, but if a blood transfusion is ever needed, people with this blood type can receive blood only from other donors who are also H deficient. (A transfusion of "normal" group O blood can trigger a severe transfusion reaction.)

Because the H antigen is the precursor of the ABO blood group antigens, if it is not produced, the ABO blood group antigens are also not produced. This can be misleading in paternity cases, a fact that has been exploited in soap opera story lines!

In Bombay, India, an individual was discovered to have an interesting blood type that reacted to other blood types in a way that had not been seen before.It was totally unique. Serum from this person contained antibodies that reacted with all other RBCs from normal ABO phenotypes (i.e., groups O, A, B, and AB) of the donor. That person's RBCs appeared to lack all of the ABO blood group antigens plus an additional antigen that was previously unknown.
In 1952, a paper about the "new blood group character related to the ABO blood group" was published. This new blood group character is the H antigen and it is the building block for the antigens of the ABO blood group.
Named for the city in which it was first discovered, the "Bombay phenotype" describes individuals whose RBCs lack the H antigen. 
As the A and B antigens cannot be formed without the H antigen precursor, their RBCs also lack these antigens. 
As a result, these individuals produce anti-H, anti-A, and anti-B and can therefore be transfused only with RBCs that also lacks the H, A, and B antigens i.e., they can only receive blood from another person with the Bombay phenotype. Because of the rarity of this blood type, this normally means using blood donations from a suitable relative .