Most a random occurrence and not due to

Most females have two X chromosomes, which is what makes them women. But what happens when there are more or less than two X chromosomes in a woman’s DNA? In this lesson, we’ll explore Turner syndrome and Trisomy X.

Aneuploidy

Jennie is a happy little girl, but she has some issues. She’s very short for her age, and her neck is very wide. Her IQ is normal for her age, but she struggles with understanding things in school, and also doesn’t understand other people and their feelings and motivations.

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Jennie’s friend Carrie has some similar problems. She, too, has a normal IQ, though hers is lower than her brothers and sister, and she also struggles in school. She’s very shy and introverted, and feels awkward around others.

But Carrie is also different from Jennie. She’s very tall, where Jennie is very short.What’s going on with Jennie and Carrie? They might have a type of sex chromosome aneuploidy, where the number of sex chromosomes in a cell is not the normal number. For example, girls normally have two X chromosomes in each cell, but some people have more or less than that. Let’s look at two genetic disorders involving sex chromosome aneuploidy in girls: Turner syndrome and trisomy X.

Turner Syndrome

Remember Jennie? She’s short for her age and has trouble in school.

She also looks a little different from other girls: she’s got a very wide neck and her fingers and toes are unusually short.Turner syndrome is a genetic disorder that affects females. It occurs when one of the sex chromosomes is missing or partially missing.

Remember that girls normally have two X chromosomes, but in Jennie and other girls with Turner syndrome, there’s only one X chromosome.What does this mean? Well, this can explain some of what makes Jennie different from her peers. Physical symptoms of Turner syndrome include short stature, wide neck, unusually short fingers and toes, small jaw, fertility issues, and arms that turn outward at the elbows, among others. So the fact that Jennie is very short, has a wide neck, and short fingers and toes, could be explained by Turner syndrome.The physical symptoms are not the only ones, though. Remember that Jennie struggles in school, despite having a normal IQ.

She also has trouble understanding others. Psychological symptoms of Turner syndrome include learning disabilities and difficulty in reading others’ emotional states.Jennie’s mom feels guilty and wonders if she did something to cause Jennie’s Turner syndrome. Is she to blame? No. Turner syndrome appears to be a random occurrence and not due to environmental factors or part of a family’s history.

Turner syndrome is essentially a genetic disorder that affects development. This could mean that it inhibits Jennie’s ability to develop physically (causing her to be short or infertile or to have issues with heart or immune system functions) and her ability to develop psychologically (causing her to have a learning disability or social issues).What can Jennie and her parents do? A doctor can create a treatment plan for Jennie. It will most likely include growth hormone therapy and estrogen to help her grow physically and go through puberty.

The doctor may also suggest other treatments to help with some of her other symptoms.

Trisomy X

Jennie’s not the only one struggling. Remember Carrie? Unlike Jennie, she doesn’t have a problem with growth; in fact, she’s grown too much and now she’s very tall for her age! But, like Jennie, she struggles some with school. Her IQ is normal, but lower than her siblings’ IQs, and she’s very introverted.

Carrie might have another sex chromosome aneuploidy, trisomy X, which is also sometimes called triple X syndrome. Trisomy X is like the opposite of Turner syndrome: instead of having fewer than two X chromosomes, a girl with trisomy X has an extra X chromosome in each cell. So instead of having two X chromosomes, Carrie has three. Pay attention to the names for this syndrome: triple and trisomy, both of which have the prefix ‘tri-,’ which means three. Thus, someone with trisomy X has three X chromosomes.Physical symptoms of trisomy X involve a tall stature, increased space between the eyes, and a proportionally smaller head size. You can remember the effect Turner syndrome and trisomy X have on height by thinking about Jennie and Carrie: Jennie is lacking an X chromosome, and she is also lacking in height because she has Turner syndrome.

In contrast, Carrie has an extra X chromosome, and has extra height because she has trisomy X. Like Turner syndrome, physical symptoms are not the only symptoms of trisomy X.Psychological symptoms of trisomy X include learning disabilities, a normal IQ that is lower than siblings’, speech and language delays in infants, delayed motor coordination, and introversion or difficulty with interpersonal relationships. The fact that Carrie has trouble in school and her IQ is lower than her brothers’ and sister’s IQs, as well as the fact that she’s very introverted, could have to do with her having trisomy X.Like Jennie’s mom, Carrie’s mom doesn’t have anything to do with her daughter’s condition. Trisomy X appears to be a random occurrence, and there’s nothing Carrie’s mom could have done to prevent it. To treat trisomy X, Carrie will need to see specialists.

These could include speech, learning, occupational, and psychological therapists. They can help her treat the symptoms associated with trisomy X, though there is no direct treatment for the chromosomal abnormality itself.

Lesson Summary

A sex chromosome aneuploidy occurs when cells have too many or too few sex chromosomes.

Turner syndrome is when a woman has fewer than the normal two X chromosomes. This causes developmental issues, and symptoms can include short stature, infertility, learning disabilities, and an inability to understand others, among other symptoms. Treatment for Turner syndrome includes growth hormone and estrogen.Trisomy X, also sometimes called triple X syndrome, occurs when a woman has more than the normal two X chromosomes. Symptoms of trisomy X include a tall stature, proportionally small head, learning disabilities, speech and language delays, issues with motor abilities, and introversion.

Both Turner syndrome and trisomy X appear to be random and not due to prenatal issues.

Learning Outcomes

After reviewing this lesson, you’ll have the ability to:

  • Recall what a sex chromosome aneuploidy is
  • Explain what causes Turner syndrome and Trisomy X
  • Describe the symptoms and treatments for Turner syndrome and Trisomy X
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