Taking Charge of Your Health

Learning medicine is hard work! Osmosis makes it easy. It takes your lectures and notes to create
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much more. Try it free today! Turner syndrome, named after Henry Turner
who first described it, is a chromosomal disorder affecting females where one X chromosome is
either completely or partially absent. Now, our DNA is this humongous blueprint of
information on how to make a human, which is usually packaged up nicely into 46 chromosomes. These 46 chromosomes come in 23 pairs – and
each pair has one chromosome from each parent. One of these pairs, the sex chromosomes, determines
person’s biological sex and it can be composed of either two X chromosomes for females or
an X and a Y chromosome for males. So, if you wanted to make another human, first
you’d have to find someone that feels the same way, and then you both contribute half
of your chromosomes. In order to package up half the chromosomes
into either a sperm cell or an egg cell, you actually start with a single cell that has
46 chromosomes. Let’s just say we’re making a sperm cell
– for simplicity, we’re only going to show one pair of chromosomes, but remember that
all 23 pairs do this. First step is meiosis, which is what produces
our sex cells, and the chromosomes replicate, and so now they’re sort of shaped like an
‘X’—even though there are two copies of DNA here, we still say it’s one chromosome
since they’re hooked together in the middle by this thing called a centromere. OK then the cell splits in two, and pulls
apart the paired chromosomes, so in each of these cells you’ve now got 23 chromosomes. Now the two copies of the chromosome get pulled
apart, and the cells split again, which means four cells, each still with 23 chromosomes. Now these are ready to pair up with an egg
cell from mom that has 23 chromosomes as well, totaling to 46 chromosomes, and voila–nine
months down the road you’ve got yourself a baby. Usually, each parent contributes one chromosome
to each pair. Fifty-fifty. Sometimes though, one parent might contribute
one chromosome too many, which is called trisomy, or one chromosome less, which is called monosomy. Monosomy is what happens in Turner syndrome
and it specifically affects the X chromosome. There are three potential karyotype scenarios
associated with Turner syndrome. Most commonly, an entire X chromosome is missing,
giving a 45, X karyotype – in other words, the person only has 45 chromosomes, missing
one of the X chromosomes. This can happen as a result of nondisjunction
of sex chromosomes during meiosis, and it happens more frequently in sperm cells – but
egg cells can also be affected. Nondisjunction means the chromosomes don’t
split apart – so following meiosis, one resulting sex cell ends up with both chromosomes and
the other gets none. Multiply by two, and the final result is 2
cells with an extra chromosome, and two cells missing a chromosome. Nondisjunction can also happen in the second
step though, so first steps goes great, and both cells have a chromosome, but if they
don’t split apart in the second step, then the final result is one cell with an extra
chromosome, one cell missing a chromosome, and two with the right number of chromosomes. Now, if an egg cell combines with any of these
sperm cells that have the missing chromosome, then you have Turner syndrome. The next most common scenario is mosaicism,
meaning the individuals have some cells in their body with the 45, X karyotype and others
with a 46, XX karyotype. This happens because of an error following
conception. So, conception results in a single cell the
zygote, that divides, over and over again, essentially producing every kind of cell in
the body. Each of these divisions is called mitosis. Nondisjunction of the sex chromosomes can
also happen during any mitosis, in which case you’d end up with one cell line that has
three sex chromosomes, so 47 in total, and one cell line missing an X chromosome, so
45 chromosomes in total. But if the prior divisions progressed normally,
there is also one cell line with 46 chromosomes that contributes cells to the developing fetus. Now, the cell line with 47 chromosomes rarely
survive, but the one with 45 does, and continues to replicate and produce more cells with only
one X chromosome, along with the 46, XX cell line, leading to a mix of 45, X and 46, XX
cells in the body. The least common karyotype in Turner syndrome
is where there’s only a part of the X chromosome missing. Basically, a section of the chromosome – for
example the short arm – is deleted at some point during meiosis, but the rest of the
chromosome is passed on. This can also happen at some point during
mitosis, and the result is another mosaic karyotype. As far as we know, these errors happen at
random, so parents who have a child with Turner syndrome are not at a higher risk than others
of having a second child with the same condition. Now, only having one complete X chromosome
impacts the female reproductive system by increasing the rate of loss of eggs, which
normally happens more slowly. By two years of age, none are left, essentially
causing “menopause before menarche”. Without eggs, the ovaries fail to develop
normally, becoming non-functional, fibrous, “streak” ovaries. These streak ovaries can’t produce sex hormones,
resulting in hypogonadism and low estrogen levels. The body will respond by producing more follicle-stimulating
hormone (FSH) and luteinizing hormone (LH) than normal, since these hormones stimulate
estrogen secretion by the ovaries. The X chromosome also carries genes that are
important for growth and development of tissues throughout the body. One of these is the short stature homeobox
– SHOX for short – gene. So having a single copy of the SHOX gene results
in, you guessed it, short stature. There are also plenty of other unidentified
genes on the X chromosome, so individuals with Turner syndrome are predisposed to cardiovascular
defects like preductal coarctation of the aorta and bicuspid aortic valve. They might have kidney issues, specifically
a congenital abnormality called horseshoe kidney where the two kidneys become fused
during fetal development. They might also have lymphatic and skeletal
abnormalities, and are at higher risk for type II diabetes and hypothyroidism. Just how many of these abnormalities linked
with Turner syndrome are actually present depends on the proportion of cells the person
has with the 45, X karyotype. Signs and symptoms of Turner syndrome vary
depending on the age of the person and on how much of the second X chromosome is missing. Infants may be born with lymphedema, or swelling
due to a build-up of lymph, in their hands and feet. Many also have lymph-related swelling of the
back of the neck, causing a cystic hygroma, which eventually decreases as they age. This often leaves extra skin on the neck,
called neck webbing, which gives the appearance of having a wider than normal neck. Coarctation of the aorta and a bicuspid aortic
valve can cause lower extremity cyanosis, meaning a bluish or purplish discoloration
of the lower limbs, and can result in congestive heart failure. Children with horseshoe kidney are more likely
to have urinary tract infections. In adolescents, skeletal abnormalities become
apparent, like short stature, a broad chest with widely spaced nipples, low-set ears and
arms that turn outward at the elbows, also called cubitus valgus. Because it causes streak ovaries, Turner syndrome
is also the most common cause of primary amenorrhea, which is when a female has not begun breast
development by age 13 or hasn’t had menarche by age 15. As a result, many females with Turner syndrome
are infertile. Karyotype analysis is the only way to diagnose
Turner syndrome. It can be done before birth via chorionic-villus
sampling or amniocentesis. Other tests can be useful for identifying
the specific developmental abnormalities caused by Turner syndrome that may be affecting the
person. For example, an ultrasound can show congenital
issues like cystic hygroma, cardiac defects, and horseshoe kidney, and a fasting blood
glucose test can help detect diabetes. Treatment for Turner syndrome usually involves
growth hormone therapy in childhood to promote height and bone growth and sex hormone replacement
therapy starting at adolescence to promote breast and uterine development. In vitro fertilization can make pregnancy
possible for some female with Turner syndrome who are infertile. All right, as a quick recap… Turner syndrome is a chromosomal disorder
where one X chromosome is either completely or partially absent. The most common karyotypes are 45, X and a
46, XX/45, X mosaic, and the impact of the disorder on the growth and development depends
on the proportion of cells affected, and on the amount of X chromosome that is missing. The most common features include streak ovaries,
short stature, lymphedema, neck webbing, and congenital heart and renal defects. Treatment involves growth hormone therapy
and sex hormone replacement therapy.

35 thoughts on “Turner syndrome – causes, symptoms, diagnosis, treatment, pathology

  1. As a human biologist I think that Turner syndrome is highly fascinating as besides symptoms such as short stature or extra skin on the neck (as Osmosis greatly explained) other characteristics such as intelligence are often not affected. It is remarkable to think that the development of people still works despite one chromosome completely missing (if you take into account that mutations in single genes can be lethal sometimes). I am planning to dive deep into prominent human genetic diseases in one of my next videos since this topic is very important and thrilling!

  2. Спасибо большое за отличные познавательные видео, но если не сложно, пожалуйста создавайте русские субтитры🙏

  3. Why will the cell line containing 47 XXX/XXY rarely survive? XXX is triple x syndrome and XXY is klinefelter right?

  4. Is there a way they can extend the underdeveloped uterus in late untreated Turner person to enable them to have in vitro pregnancy

  5. I am a 66 year old woman with Turner's mosaic and this video provided more technical information than I've ever known about my condition. Really well done explanation and visuals! Thank you so much! Because of my age, I was not diagnosed until my late teens and never was offered growth hormones.

  6. I’m doing a research paper on Turner syndrome and a question I had to answer was of where and why was it prevalent? If anybody could give me an answer ASAP it would be great thanks!

  7. what is happen when 22x chromosomes of female is fused with 22 chromosomes of male due to failure of disjunction of x and y chromosome?

  8. Still struggling to understand something… In normal XX female cells one of the X chromosomes is inactivated anyway, so what exactly causes the symptoms of Turner syndrome?

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