[Music] 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 a person's biological sex and can be made up 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 4 6 chromosomes let's just say we're making a sperm cell for Simplicity we're going to show one pair of chromosomes but remember that all 23 pairs do this the 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 okay then the cell splits into into 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 chromosomes 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 9 months down the road you've got yourself a baby usually each parent contributes one chromosome to each pair 50/50 sometimes though one parent might contribute one chromosome to many and this is called triom 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 kot type scenarios associated with turner syndrome most commonly an entire X chromosome is missing giving a 45x kot type in other words the person only has 45
chromosomes missing one of the X chromosomes this can happen as a result of non-disjunction of sex chromosomes during meiosis and it happens more frequently in sperm cells but egg cells can also be affected non-disjunction means the chromosomes don't split apart so following meiosis one resulting cell ends up with both chromosomes and the other gets none multiply by by two and the final result is two cells with an extra chromosome and two cells missing a chromosome non-disjunction can also happen in the Second Step though so first step 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 Chrome Rome then you get Turner syndrome the next most common scenario is mosaicism meaning the individuals have some cells in their body with the 45 xot type and others with a 46 XX carot type 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 non-disjunction 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 progress normally there's also one cell line with 46 chromosomes that contribute cells to the developing fetus now the cell line with 4 47 chromosomes rarely survive but
the one with 45 does and continues to replicate and produce more cells with only 1 X chromosome along with a 46 XX cell line leading to a mix of 45x and 46 XX cells in the body the least common kot type in Turner syndrome is where there's only 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 kot type
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 menarchy 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 or FSH and lutenizing hormone or LH 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 gene or S Hawks for short so having a single copy of the S Hawks Gene results in you guessed it short stature there are also plenty of other unidentified genes on the X chromosome so individuals with erer 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 a higher risk for type 2 diabetes and hypothyroidism just how many of these abnormalities linked with turner syndrome are present depends on the proportion of cells the person has with the 45x kot type 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 lymphadema or swelling due to a buildup 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 adolescence skeletal abnormalities become like short stature and 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 Amara which is when a female hasn't begun breast development by age 13 or hasn't had menarchy by age 15 as a result many females with turner syndrome are infertile car stereotype analysis is the only way to diagnose Turner syndrome it can be done before birth by
chonic Villa 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 invitro fertilization can make pregnancy possible for some females 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 kot types are a 40 5x and a combination of a 46xx and 45x 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's missing the most common features includes streak ovaries short stature lymphadema neck webbing and congenital heart and renal defects treatment involves growth hormone therapy and sex hormone replacement therapy helping current and future clinicians Focus learn
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