Why do individuals with Turner's syndrome (XO sex chromosomes) not have ovaries?

Submitted by KissMyAFF t3_yrtsd5 in askscience

The way I understand it, the SRY gene is found on the Y chromosome, and it encodes for TDF. This, in turn, leads to prenatal testosterone and AMH. The prenatal testosterone lead to the development of the male reproductive system from the Wolffian duct while AMH leads to the disintegration of the Mullerian duct. Conversely, if there is no Y chromosome and no upsurge of testosterone or presence of AMH, the Wolffian duct disintegrates while the Mullerian duct develops into the female reproductive tract.

In that case, it seems like people with XO genotypes have no Y chromosome = no TDF = no AMH/high levels of T, so they should develop ovaries. What am I missing?

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EDIT: Thank you so much everyone! This was super interesting. Just a follow-up, if anyone's still lurking here - would people with Turner's syndrome be more susceptible to X-linked diseases?

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Pythagorantheta t1_ivwlz0w wrote

the lack of the second x chromosome means that many protein and endocrine pathways do not develop. The shield chest is an example, one x chromosome will not give any female breast tissue. You could look at Kleinfelter males as an example of too much x chromosome products are made. As to your specific examples, I've been out of human genetics for a while. sorry if this is not what you are exactly looking for

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calvinball_hero t1_ivwou3l wrote

I don't know off the top of my head, but some quick googling led me to this 2014 paper. The aneuploidies section has some relevant discussion, including details on at least one gene on the X chromosome which we seem to need two copies of, for normal ovary development.

It seems like your crude outline above is correct, but there is much more complexity to the normal development of ovaries beyond this.

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pokerchen t1_ivxrk8f wrote

Speaking in general about genetic expression and regulation, it's not just whether you have genes but also how many copies you have. Even though additional copies of X in a cell are packed away as Barr Bodies, this does not mean that they are completely silent.

So... people with XO end up with ovaries, but they are not functional for additional reasons.

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marieterna t1_ivxtpw0 wrote

I believe ~10-15% of genes on the Barr Body escape X-inactivation. This means that in the X0 genotype, you are missing those 10-15% genes and their expression, which is an issue. It’s the opposite in Klinefelter’s, XXY genotype. Because you have two X chromosomes, one undergoes X-inactivation which is to be expected in the XX genotype. But you have 10-15% MORE due to that Barr Body, since in a normal XY genotype, you’re not supposed to have that extra X.

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betterbuka t1_ivxyzlp wrote

Idk if this helps but whenever that finding is described in medical school, it’s called ‘streak ovaries’ so they do have ovaries or at least the rudimentary portions of ovary but bc they’re missing the second X chromosome for completion, they have things like stream ovaries, little/no breast development, etc.

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Kyrthis t1_ivy4kvx wrote

Replying to pokerchen (#500,316)

That is how it works for autosomes. Sex chromosomes, however, work with a single copy always. The Y is always alone in a cell. In females, only one X is being transcribed due to random X inactivation, which is what creates Barr Bodies.

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Cultural-Opposite937 t1_ivya4b2 wrote

Replying to marieterna (#500,411)

This is correct, the region that isn't inactivated is called the psudoautosomal region and is what allows the pairing between the X and Y (or two Xs) during meiosis.

People with only 1 X have haploinsufficnacy for the genes in this region and that leads to the alteration in their phenotype, including non-functioning ovaries or streak gonads (phenotype can vary).

Those with trisomy of the sex chromosomes (XXX, XXY, XYY) may also have altered phenotype due to overdosing of the genomic products of these regions (though XXY tends to have more effect than XXX and XYY doesn't seem to have much effect at all, despite what early studies may claim). Instances of these are also much higher than Turners syndrome (1 in 500 for XXX and 1 in 1000 for XXY and XYY)

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Emily_Ge t1_ivydfll wrote

Replying to Pythagorantheta (#498,588)

More specifically: while one X chromosome usually gets deactivated in XX women, this inactivation ist complete. An XX Woman has one whole X chromosome and about 15% of the remaining X chromosome active for protein production.

X0 individuals will lack this genetic information and thus some proteins are produced in less quantity than usual. Which leads to incomplete sex development.

Thus since X0 individuals don‘t have the regular 15% extra X, they cannot properly develop gonads in the first place. Despite the later pathways being set to ‚female‘

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F0xFiree t1_ivyf7et wrote

Uh hi I actually have turners syndrome. Mosaic turners to be more specific. This means some of my genes are missing an X chromosome and some have an xxxy thing. I had two ovaries. My left was abnormal; it was described as streaked, flat and generally not formed and was probably nonfunctional. It was removed during the c section delivery of my youngest child. My right one however works just fine. Proof for that is that I’ve conceived naturally and have two kids to show for it.

Due to my genetic make up though, having ovaries when having an xxxy chromosome make up gives me a much higher chance of developing tumors so my remaining ovary is being plucked out next week. Hope this info from someone’s personal experience helps!

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silvandeus t1_ivytq5t wrote

Replying to F0xFiree (#501,608)

Forgive me but I am curious, what are the odds of passing on such chromosomal content to your offspring? Would only those zygotes with expected chromosomal content be viable?

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Sicon3 t1_ivywybl wrote

Replying to silvandeus (#502,371)

Turner syndrome is caused by an abnormality in the sperm or egg cell itself hence it occurs naturally in the population. Turner syndrome usually causes infertility but as in the above individuals case it doesn't always cause infertility. A person with turners syndrome is (to what knowledge I have and can find) not significantly more likely to produce abnormal eggs than anyone else.

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F0xFiree t1_ivyz2yx wrote

Replying to Sicon3 (#502,550)

Bingo. Also, plenty of women who have turners syndrome don’t even find out they have it until later in life when they’re ready to have children. They seek medical help when they have trouble conceiving, and this is what usually leads to the discovery of turners in the first place.

My situation was not entirely unrelated to the described scenario above, however I was actually already newly pregnant with my second child and my prenatal blood work had come back with some concerning markers that eventually led to a diagnosis of turners syndrome in myself. I would likely have never found out had I not gotten pregnant again. I’m pretty short (which is one big side effect of having turners) but women being short runs in my family on both sides already and the type of testing that had started all of this for me wasn’t routine when I had been expecting my first child. I could have probably never questioned it or other things tied to my diagnosis. Life’s funny like that I guess.

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Cannie_Flippington t1_ivz1ird wrote

Replying to silvandeus (#502,371)

Internet says it's not directly inherited. Which makes sense since it's a mutation during meiosis so the resulting gamete would be XX, XY, X-, or Y-. In order to be inhereted the germ-line cells would all have to be XX or XY in someone with three chromosomes and would be incomplete in someone who had only partial XX or XY and they would likely have pretty severe fertility issues. At least 50% of all first trimester miscarriages are due to chromosomal instability, and being XXY, X, X+, Y, Y+, or XYY all qualifies. For contrast, the number of chromosomally abnormal living people is about .5%. If all the germ line cells of someone who was chromosomally abnormal were also abnormal... that's not great odds for having kids.

Male XYY aren't sterile, but male XXY usually are - but this is because of their testes not working properly, not necessarily what they would produce if they had functional ones.

Most Turner's women are sterile for the same reason - their ovaries just don't work properly. OP lucked out that the ordinary redundancy of the second ovary yielded a functional one and is a perfect example that their gametes are not effected by their own abnormality.

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F0xFiree t1_ivz57ul wrote

Replying to Cannie_Flippington (#502,813)

>Most Turner's women are sterile for the same reason - their ovaries just don't work properly. OP lucked out that the ordinary redundancy of the second ovary yielded a functional one and is a perfect example that their gametes are not effected by their own abnormality.

Yes exactly! I was called a “medical marvel” by my genetic counselor for conceiving not one but two children with little to no difficulty. Something about my specific mosaic make up with my turners really let me “get off easy” when it comes to some of the physical side effects of having it. I have no heart liver or kidney issues, no trouble having kids, etc. I’m just short as hell unfortunately hahaha

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pokerchen t1_ivzezk9 wrote

Replying to Kyrthis (#500,986)

There are special mechanisms that permit certain DNAs to still function within the Barr Bodies. I'll share this article with you as a quick Google search: https://phys.org/news/2016-07-scientists-untangle-barr-body-inactive.html

Learned about how BBs are not silent while chatting with a professor in 2006. I suspect we don't know the exact details just yet, but could do a proper literature search. (Note: expertise is structural biology/biophysics. Almost went into epigenetics instead.)

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