Everything You Need to Know About Turner's Syndrome
Turner’s syndrome is a genetic disorder that affects the sex chromosomes. It’s characterized by the total or partial absence of an X chromosome, so it only affects women. The karyotype will therefore be 45X.
Naturally, the presence of a single X chromosome affects the development of primary and secondary female sexual characteristics.
Statistically, 50% of Turner’s syndrome cases have a karyotype of 45X, where there is a total loss of the second chromosome. Fifteen percent only have partial loss of this chromosome. In these cases, either the long or the short arm of the chromosome can be affected.
The remaining cases are mosaicisms. These are characterized by the presence of two or more cellular lines with genetic alterations. In this way, these people will have some genetically normal cells (45XX) and some genetically altered cells (45X).
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Sex chromosomes under normal conditionsUnder normal conditions, everyone has 23 pairs of chromosomes. Of these, 22 correspond to the non-sexual autosomes or chromosomes, and the final pair is the sexual pair.
The sex chromosomes, where one is inherited from the father and one from the mother, determine the genetic sex of a baby.
- The presence of two X chromosomes (46XX) determines that the sex will be female. Thus, female primary and secondary sex characteristics will develop.
- The presence of a Y chromosome (46XY) determines that the sex will be male. Thus, this leads to the development of masculine primary and secondary sexual characteristics.
What happens with Turner’s syndrome?
Before we go into the explanation of this chromosomal anomaly, it’s important to recall certain aspects of reproductive cellular division (the gametes).
This process is known as meiosis, and it occurs in two phases known as meiosis I and meiosis II. Overall, the goal is to produce daughter cells with half the genetic information from the original cells.
- Basically, you start with a stem cell that contains 23 pairs of chromosomes.
- After meiosis I, there are two daughter cells that each have 23 chromosomes.
- After meiosis II, each of these two cells will produce two other cells with 23 chromosomes.
- Therefore, one diploid stem cell will produce four haploid daughter cells.
How does a cell lose a chromosome, then?
The prevailing theory is that the loss of this second X or Y chromosome occurs after conception. That means that it is a failure in the division of the cells.
The absence of a Y chromosome determines the development of female sexual characteristics. Even if the original cell was XY, its loss will lead to female development.
Clinical symptoms of Turner’s syndrome
- Delay in growth during childhood and small stature during adulthood.
- “Sphinx”-like facial characteristics, with a flattened nasal bridge, low-set eyes, and slight malformation of the eyelids.
- A shorter and wider neck than usual, with a very low hairline.
- Numerous pigmented moles.
- A wide thorax and underdeveloped nipples that are set widely apart and with a childlike appearance.
- Secondary sexual characteristics are very underdeveloped, with sexual infantilism present. There is no development of the breasts, very little pubic hair, and rounded hips. All of this is due to a lack of estrogen.
- Bone malformations are very common, such as one that causes the arm to angle outward.
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Unfortunately, this condition can also bring with it various internal disorders, such as:
- Congenital heart disorders like aortic coarctation and other valvular malformations are very common.
- Kidney problems may appear in a significant number of patients, most commonly horseshoe kidney.
- Gonadal dysgenesis. In this case, he ovaries are not well developed, and gonadal bands are present instead. This leads to hypergonadotropic hypogonadism, which means that while all the stimuli needed for the production of estrogen are present, they are not produced by the absence of ovaries.
- Amenorrhea (the absence of menstruation) and infertility. Only a small percentage of patients are fertile. This is one of the most common characteristics of Turner’s syndrome.
DiagnosisTurner’s syndrome can be difficult to diagnose. Most women with this disorder don’t have very obvious features: they are milder phenotypes, because the more severe cases are naturally aborted.
About one third of cases are identified as newborns. The presence of certain physical features and signs of heart disease are suspicious characteristics. Another third of cases is diagnosed during childhood, mainly because of their short stature.
Finally, the last third is diagnosed during adolescence. In these cases, short stature combined with sexual infantilism become clear when the patient never reaches puberty.
Hormone replacement therapy using estrogen helps with the development of sexual characteristics, but it doesn’t correct infertility. During childhood, it’s recommended to treat these girls with growth hormones that will help normalize their stature.
Can they have children?
Yes, it’s possible for women with Turner’s syndrome to bear children. A small percentage of people with Turner’s syndrome are fertile and would have no problems conceiving.
In cases of infertility, which is most common, in-vitro fertilization techniques are required using donated eggs. The egg is fertilized by sperm in vitro and implanted into the patient afterwards. These pregnancies demand a much more rigorous level of control than a normal pregnancy.