moles!

[nocallaochicas]

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I don't know much about Ob/Gyn and Step 2 is forcing me to learn at least a little. I am stuck on moles. Complete moles. Since you folks know about these pregnancy things the most, I am asking for your help. If I should be asking in the USMLE forum, just let me know.

The Q/my problem: Robbins tells me that complete moles come from a sperm's haploid DNA developing in an empty egg. It then says, these completes can be 46, XX or 46, XY - all from sperm DNA from one duplicated haploid or two haploids from two sperm. What about one sperm's 23 Y DNA duplicating giving a complete mole of 46, YY? Why isn't that mentioned?

I am not sure if I am misunderstanding the genetics or if a 46, YY just doesn't "grow" past the "one cell" stage. Please help.
sincerely, the one called "nocallaochicas"

 

[Pfannenstiel]

Congratulations, you understand this better than you think. Complete moles are formed by fertilization of a so-called "empty egg" (one which lacks maternal genetic material). The most common scenario is fertilization by a single sperm. Theoretically, this could result in a 46XX karyotype (based on duplication of a 23X sperm) or a 46YY karyotype (based on duplication of a 23Y sperm). However, the 46YY has never been reported and is presumed to be nonviable due to the absence of an X chromosome, which is believed to be necessary for survival. The less common scenario is fertilization of the "empty egg" by 2 sperm. Again, theoretically, this could be 46XX, 46XY, or 46YY. The 46XX would look just like a single-sperm mole on karyotype; the 46YY would not be viable because of the absence of the X; and the 46XY remains as the one everyone talks about - because if you have a 46XY complete mole it *had* to come from 2 sperm.

 

[nocallaochicas]

Hey - thanks.
The more I thought about it after posting, the more I realized it must be true that 46, YY just isn't viable. Thank you for confirming that. Textbooks should explain it; especially Robbins.
Again, thank you.
ncc