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Difference Between Classic and Mosaic Turner Syndrome
Turner syndrome is a genetic disorder that affects only females and is characterized by a missing or incomplete X chromosome. There are two main types of Turner syndrome: classic Turner syndrome and mosaic Turner syndrome. The main difference between the two lies in the way the missing X chromosome is present in the body.
What is Classic Turner Syndrome?
Classic Turner syndrome is caused by the complete absence of one X chromosome in every cell of the body. This means that every cell in the body has only one X chromosome instead of the usual two. This type of Turner syndrome affects approximately 50% of individuals with the condition.
What is Mosaic Turner Syndrome?
Mosaic Turner syndrome, on the other hand, is caused by the presence of a mixture of cells with different numbers of X chromosomes in the body. In this type of Turner syndrome, some cells have two X chromosomes while others have only one. This is because the loss of an X chromosome occurred after the cell division had started, which resulted in some cells having two X chromosomes and others having only one. Mosaic Turner syndrome affects approximately 10- 15% of individuals with Turner syndrome.
Causes − The cause of mosaic Turner syndrome is some type of error that occurs during cell division, leading to abnormalities in the chromosomes of some but not all of the cells.
Diagnosis − Diagnosis of mosaic Turner syndrome may be more difficult since not all the cells have a chromosomal abnormality. However, the presence of the features seen in Turner syndrome may be present and the chromosome abnormality may sometimes be detected with molecular methods such as RT-PCR and using karyotypes. In some variants of mosaic Turner syndrome, the individual may be born with ambiguous genitalia which may also indicate a chromosomal issue. Some of the cells are normal in terms of chromosomes, but others are not.
Symptoms − Some females with mosaic Turner syndrome can have eye problems and in fact, have problems with the development of the eye called anterior segment dysgenesis. Many of the typical features of Turner syndrome are present including the short stature, low set eyes, and webbed neck. Similar organ problems may be present an in some variations, the genitalia may be ambiguous. Mixed gonadal dysgenesis (MGD) is another problem that can occur in which some testicular tissue may be present along with streaks of ovary tissue. This condition is linked to a specific gene called SRY.
Treatment − Individuals with Turner syndrome can be treated with growth hormones to encourage growth and hormone treatments at puberty. Researchers have also suggested that in some cases, such as in the presence of the SRY gene that removal of gonadal tissue is recommended to reduce the risk of gonadoblastoma.
Differences: Classic and Mosaic Turner syndrome
The symptoms of both classic and mosaic Turner syndrome are similar, but the severity of the symptoms can vary. Some of the most common symptoms of Turner syndrome include short stature, infertility, and heart defects. However, individuals with mosaic Turner syndrome often have milder symptoms than those with classic Turner syndrome, as they have some cells with a normal number of X chromosomes.
Treatment
In terms of treatment, individuals with both classic and mosaic Turner syndrome may benefit from hormone replacement therapy to help with growth and development. However, those with mosaic Turner syndrome may have a better response to the therapy than those with classic Turner syndrome, as they have some cells with a normal number of X chromosomes.
The following table highlights the major differences between Classic Turner Syndrome and Mosaic Turner Syndrome −
Characteristics |
Classic Turner Syndrome |
Mosaic Turner Syndrome |
|---|---|---|
Definition |
Classic Turner syndrome is the disorder in which one of the X chromosomes is missing from every cell of the body. |
Mosaic Turner syndrome is the disorder in which usually one of the X chromosomes is missing from some of the cells of the body. |
Number of body cells impacted |
In classic Turner syndrome, all the cells of the body are affected. |
In mosaic Turner syndrome only some of the cells are affected. |
Genotype |
The genotype of classic Turner syndrome does not vary and is 45,X. |
The genotype of mosaic Turner syndrome is very variable and can be any of the following: 45,X/ 46,XX or even 45,X/47,XXX, or 45,X/46,XY. |
Prevalence |
The classic Turner syndrome is found in about 45% of Turner cases. |
The mosaic Turner syndrome is found in about 55% of Turner cases. |
Diagnosis |
RT-PCR and other molecular techniques will always diagnose classic Turner condition. |
The RT-PCR and other molecular techniques do not always diagnose mosaic Turner condition immediately because the problem is only in some of the cells. |
Complications |
Common complications of classic Turner syndrome include dissecting aortic aneurysm and kidney problems. |
Complications of mosaic Turner syndrome include gonadoblastomas in certain genotypes. |
Conclusion
Classic Turner syndrome and mosaic Turner syndrome are two different forms of the same genetic disorder. The main difference between the two is the way the missing X chromosome is present in the body.
Classic Turner syndrome is caused by the complete absence of one X chromosome in every cell, while mosaic Turner syndrome is caused by the presence of a mixture of cells with different numbers of X chromosomes. Both types of Turner syndrome result in similar symptoms, but the severity of the symptoms can vary.
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