Step I 46XY and 45X

[syoung]

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full term girl is examined shortly after birth. small for gestational age, excess skin on nape of neck and lymphedema of hands and feet. chromosomes show normal 46XY and some cells w/ 45X. which can explain this?

mitosis ND
reciprocal translocation
roberts translocation
skewed x-inactivation
uniparental disomy

i was thinking about roberts as my number 1, thinking maybe the Y hopped onto the X in some of those cells; my second guess was reciprocal translocation.
i ruled out skewed x-inactivation b/c that doesn't make sense, this is a boy by default, and didn't think mitosis ND because that should show some cells w/ just 45Y; didn't think it was uniparental disomy b/c that would probably show some sort of duplication...

any thoughts?

 

[aspiringmd1015]

for roberts you need acrocentric chromosomes, not 100% sure, but acrocentric arent the sex chromosomes. Patient has mosaicism for x and y.

 

[theacks1]

I assumed it was a mitotic nondisjunction, with any resulting 45Y cells being unable to survive. The X chromosome has some important genes necessary for life, and I assumed that went to the cellular level as well.

A quick look turns up a few articles for 45,x/46XY mosaicism, including a case report in Hormones a few years back, stating "45,X/46,XY mosaicism is considered a postzygotic mitotic error. Loss of the Y chromosome by 'non-disjunction' after normal disomic fertilization leads to the 45,X cell line." It doesn't seem to go much further that that, but it makes sense to me. http://www.hormones.gr/835/article/article.html

 

[syoung]

thanks! ya my thought process was def wrong.

mitotic ND ftw