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QUESTION: What is the Bombay phenotype? I understand it to make some people type O. Is that true?
ANSWER: ABO blood type antigens are produced by ABO enzymes that are coded by our ABO genes. Type O does not make a true antigen, although they do make 'H' which is used by the other blood types as the basic bulding block. Thus, even A's and B's make H (in addition to their own A or B antigen), whilst O only makes H.
An interesting situation arises when an individual is not able to make the "H" antigen. Such a person cannot produce the "H" antigen and even if the "A" or "B" enzymes are present, cannot make "A" or "B" antigen since there is no precursor for the antigens to act upon. An individual who cannot produce the "H" antigen will appear to have blood type "O" since this blood type is a negative category (not- A, not- B, not- A and not- B ). This was first documented in Bombay and has become known as the Bombay phenotype.
The Bombay phenotype group derives the name "Bombay" because it was first discovered to exist among some people living in the region of Bombay, India. Although the group is more likely to occur in East Indians, it is a very rare group even among this population. Also, it is not restricted to East Indians and has been found to exist in Caucasians, Negroes, Japanese, etc.