Q: What will happen if the chromosome paired as YY or XYY ?
A: Good question! As we presented at MiniMed school, the normal male chromosome complement is 46,XY; the normal female is 46,XX; reflecting the fact that you need a single active X chromosome - all additional X's will be inactivated.
We do see mis-segregation of the sex chromosomes resulting in individuals with extra X's (or Ys), but we never see one without a single X as there are ~1000 genes on the X, so we need at least one copy of them.
On the other hand, about 1 in 1000 males has an extra Y chromosome so that there is one X and two Y chromosomes. Fertility and appearance is normal but males with this finding tend to be taller than other family members. Early reports suggesting that XYY males had a tendency to aggressive and criminal behavior were controversial due to biased ascertainment schemes. More recent studies suggest that possible behavioral problems may be attributable to those cases with a reduced IQ rather than an increase in testosterone level or other effects of an imbalance in sex chromosome gene expression. Nonetheless, although speech delay is common, IQ is generally not reduced (Linden et al. 1996).
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Q: You mentioned some complications with imprinting around IVF babies. I am the mother of a 16 year old IVF son - can you tell me more about this? Is this a long-term concern or a petri-dish concern?
A: Thank-you for your question. There have been several reports that imprinting errors leading to both Angelman syndrome and Beckwith-Wiedemann Syndrome are increased in children born after IVF. As these are very rare in the general population, they are also still very rare among IVF newborns. However, changes in methylation at the IGF2 locus (insulin-like growth factor 2) have also been reported as increased in both cows and mice after IVF and these findings have raised concerns that more subtle epigenetic changes might be missed in IVF-conceived children. Nonetheless, as yet there have been no further data to suggest that there are any epigenetic differences between IVF and naturally conceived children. Furthermore the data on long term follow-up does not show any convincing differences in development one way or the other at this point in time. In addition, there has since been data presented suggesting that imprinting errors are more common among infertile couples also, suggesting it may be the infertility rather than IVF that is the issue.
So basically the answer is: at this point there is no evidence of a long-term effect and I do not believe this should be any concern to current parents of healthy IVF conceived children. However, as Dr. Cheung pointed out in his talk, we really don't have the data to fully assess whether there are any subtle differences in long-term outcomes of IVF that affect a small number of cases and this is an important area for further research.
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