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A blood typing mystery

19 Nov

A positive blood typing example, thanks to biologycorner.com for the figure

A commenter raised the following as an example of a highly unusual blood type pattern within a family.

 Given:

Parent #1 (female) Blood type O- (i/i,Rh-/Rh-)

Parent #2 (male) Blood type AB+ (IA/IB, Rh+/?)

Child #1 O- (i/i,Rh-/Rh-)

Child #2 Blood type AB+ (IA/IB, Rh+/?)

Is this possible?

Indeed, this is a highly questionable situation. Given that the genetics of ABO typing are fairly well described, the situation described raises a lot of flags. Assuming what is presented is an honest case, it would be extraordinarily interesting to investigate.

If I were asked to solve this, I would probably pursue the following ideas…

Before doing anything else, I would have everyone in the family re-typed. Since questions have been raised, I would insist that they were all re-typed at least three times at three facilities (or at least using different lots of the test reagents). I would also question the original typing location about the reagents used in the initial test and pursue whether any additional questionable typings were reported. Additionally, records should indicate the lots used for the original typing. I would question the company that produced these reagents about Quality Assurance and any known problems with these lots.

The commenter also indicated that he knew of several couples with this situation (which would be extraordinary). Again, this is unlikely, so the local testing facility  and its quality remain likely sources of error.

Luckily, an explanation for the Rh types of both child is possible. Assuming the father is Rh+/Rh-, and the mother is Rh-/Rh-, children could easily have either type. This is a relief, because the Rhesus gene has a large number of alleles making it more complex genetically.

Regarding ABO types, the simplest explanation for Child #1 is that it is not the father’s child. This leaves the ABO type of child#2 in question. Assuming the retyping tests suggested above come back completely supporting the original characterization, I would like to see the birth records for the child to verify that it was not adopted or even somehow ‘switched at birth’. The best verification would be an RFLP analysis of both parents and the child. This is the ‘DNA Fingerprinting’ that is talked about in the courtroom.

Probably the most interesting explanation is that the mother is a chimera. This rare condition arises when an individual starts out life as two non-identical twins that fuse early in development to become a single person. Confirming this would require a battery of RFLP tests from different locations of the body.

To be honest, I suspect this example to be apocryphal. But it provides a great example for describing how science is done. It is always important to remember that the tests we are talking about are just tools and subject to all the weaknesses of any other human pursuit. If we found fingerprints at a crime scene, we could feel quite confident that the owner of those prints was present at some time, but we don’t know with certainty that that person is actually guilty. Thank you very much for providing the topic!

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Posted by on November 19, 2012 in Uncategorized

 

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