Re: Re: Can a chinese parent with AB blood type have a child with O type?

A nice background explanation on the Bombay Blood Group can be found in the ABO Blood Group System section of these Intro. to Blood Bank Lecture Notes, from Madison Area Technical College. There is another tutorial on The ABO Blood Group System, from RMIT Univ., with a section that describes the properties of The Bombay, Para-Bombay and Other H Deficiencies in greater detail. Finally, the Wikipedia Online Encyclopedia also has a brief, concise explanation of Bombay phenotype inheritance in the section describing Blood Type.

In summary, the para-Bombay phenotype is apparently not as clear-cut as the Bombay with respect to AB antigenicity. With the Bombay phenotype, A & B antigens are not glycosylated, so those individuals would be antigenically equivalent to the O blood type. In the para-Bombay phenotype, there is still a low level of H fucosyltransferase activity, which may or may not result in the appearance of a weak A or B blood typing, depending how low the activity is. As far as I can tell, there are no other circumstances to explain a "parent with AB blood type hav[ing] a child with O type", as long as the paternity of that child is certain.

As described in Charles Harris's previous MadSci Genetics Network Answer to a similar question, Rambam-Hasharon syndrome is known to be associated with the Bombay blood phenotype, but I could not find any evidence for its association with the para-Bombay phenotype. However, it's important to bear in mind that this is a very rare syndrome that has not been as well-characterized as the Bombay phenotype, so there may simply not yet be enough cases to support such an association.

Finally, it is important to remember that any child of a parent known to have either the Bombay or para-Bombay phenotype would have to inherit another recessive allele from the other parent in order to display the Bombay phenotype themselves, as described in the Blood Type secton of the Wikipedia Online Encyclopedia. Since it is a recessive disorder, inheritance of one dominant wild-type, or "normal", allele would result in offspring that would display the correct ABO antigenicity. If the Bombay/para-Bombay parent, who carries 2 mutant alleles, had a child with someone who had 2 wild-type alleles, the offspring would all be heterozygous carriers of a mutant allele, but would not express the Bombay/para-Bombay phenotype themselves. If the Bombay/para-Bombay parent had a child with someone who was a heterozygous carrier with 1 mutant allele, the offspring would have a 50% chance of being carriers & a 50% chance of inheriting the homozygous phenotype themselves. Only in the unlikely event of both parents carrying the homozygous Bombay/para-Bombay phenotype would the offspring be certain to inherit the homozygous phenotype themselves.

Thanks for the interesting question,

Jeff Buzby, Ph.D.
CHOC Research Institute
MadSci Genetics Network