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.
They can accept blood only from another Bombay Blood type individual, and not from anyone who is O, A, B or AB type.
It was in 1952 that Drs. Y.M. Bhende, C.K. Deshpande and H.M. Bhatia of the Seth Gordhandas Sunderdas Medical College, Mumbai published a note in The Lancet (pp. 903-4, May 3, 1952) about two patients (X, a railway worker and Y, a stab wound victim) who needed blood transfusion. None of the blood types known until then worked for them. The moment their blood samples were mixed with any of the above types, the blood coagulated or clumped up. The doctor trio tried the blood of over 160 donors and found at last that one from Mr. Z, a resident of Bombay, suited the type of both patients X and Y. This donor blood type was then named by Dr. Bhende and others as the ‘Bombay Blood Type.’ Technically it is now termed the (hh) type of blood.
It is largely because of extensive inbreeding within the same lineage or close-community marriages, often consanguineous, such that the ‘blood type’ or the gene pool is greatly restricted. Such intra-community marriages have happened in small isolated communities such as the gypsies, Russian Jewish or Parsi communities. It is thus likely that the Bombay Blood types have common ancestral origins. This special feature is occasionally dramatized in plays and movies.