Bombay Phenotype (redirected from Hh antigen system)

Bombay phenotype

[bombā′]

Etymology: Bombay, India, where first reported

a rare genetic trait involving the phenotypic expression of the ABO blood groups. The gene for the H antigen, which in the usual dominant form of HH or Hh is responsible for the precursor necessary for the production of the A and B antigens, is homozygous recessive in individuals with this trait so that the expression of the A, B, and H antigens is suppressed. Cells of such individuals are phenotypically of blood type O, and the serum contains anti-A, anti-B, and anti-H antigens. In such cases the offspring from two phenotypic O blood type parents may be blood type AB. The phenomenon is an example of the intricate interaction of linked genes in which one gene on a chromosome controls the expression or suppression of another gene that is not its allele. See also ABO blood group.

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Bombay Phenotype

A rare variant of ABO antigens on RBCs
Physiology For A or B antigens to be expressed on RBCs, the cells must have a precursor substance—H antigen encoded by the H gene; Oh type RBCs do not agglutinate with antisera containing anti-A, anti-B, or anti-H type antibodies as they lack the H gene, and ergobstance; Oh subjects do have anti-A, anti-B, and anti-H antibodies in their serum, which may cause problems when cross-matching donors and recipients