westernmed007

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Had a question that informed me that MCC Turners was Mosaicism, then I read Goljan today and he says it's non-disjunction.... Anyone care to shed any light on this conundrum?
 

Fuzuli

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Because numerical abnormalities originate in meiosis, affected individuals have missing or extra chromosomes in all cells. In a small proportion of cases, a mitotic nondisjunctional event occurs at an early stage in an individual with an initially normal chromosome constitution. Alternatively, a "normalizing" mitotic nondisjunctional event may result in a normal chromosome complement in some cells of an embryo. In either case, the embryo is a mosaic, with some cells bearing a normal chromosome constitution and others an aneuploid number of chromosomes.The phenotypic consequences are difficult to predict because they depend on the timing of nondisjunction and the distribution of normal and abnormal cells in different tissues. Nevertheless, mosaicism may lead to clinical abnormalities indistinguishable from those of nonmosaic individuals; for example, nearly 5% of all cases of Down syndrome involve individuals with mosaic trisomy 21, and about 15% of individuals with Turner syndrome are mosaic for various sex chromosomal constitutions as described above.

("Chromosome Disorders", Harrison's Principles of Internal Medicine, 17th Edition)
 

MedLover25

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Had a question that informed me that MCC Turners was Mosaicism, then I read Goljan today and he says it's non-disjunction.... Anyone care to shed any light on this conundrum?
if both were answer choices on a test, i'd go with non-disjunction
 

mudphudwannabe

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What does MCC stand for? What I remember about mosaicism is that it is really, really rare. I'm not really sure what mosaicism has to do with Turner's syndrome, though - in the cases I remember learning about, as Fuzuli noted, mosaicism refers to a person having some cells with a normal karyotype and some cells with an abnormal karyotype.
 

It'sElectric

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What does MCC stand for? What I remember about mosaicism is that it is really, really rare. I'm not really sure what mosaicism has to do with Turner's syndrome, though - in the cases I remember learning about, as Fuzuli noted, mosaicism refers to a person having some cells with a normal karyotype and some cells with an abnormal karyotype.
Some cells are XO, some are XX.
 

DragonWell

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Because numerical abnormalities originate in meiosis, affected individuals have missing or extra chromosomes in all cells. In a small proportion of cases, a mitotic nondisjunctional event occurs at an early stage in an individual with an initially normal chromosome constitution. Alternatively, a "normalizing" mitotic nondisjunctional event may result in a normal chromosome complement in some cells of an embryo. In either case, the embryo is a mosaic, with some cells bearing a normal chromosome constitution and others an aneuploid number of chromosomes.The phenotypic consequences are difficult to predict because they depend on the timing of nondisjunction and the distribution of normal and abnormal cells in different tissues. Nevertheless, mosaicism may lead to clinical abnormalities indistinguishable from those of nonmosaic individuals; for example, nearly 5% of all cases of Down syndrome involve individuals with mosaic trisomy 21, and about 15% of individuals with Turner syndrome are mosaic for various sex chromosomal constitutions as described above.

("Chromosome Disorders", Harrison's Principles of Internal Medicine, 17th Edition)
Harrison's 16th ed. says 50% of Turner's are 45 XO, 25% are XX,XO mosaic, and 25% other X abnormalities. So it appears to agree w/ Goljan.
 

polyposis

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This is an important concept for Down Syndrome too, it came up in a UW question (three different ways to get Downs and the one option listed was mosaicism). I doubt they would ask "which is the most common" so much as "how could this have happened" with one of the three being an option.
 

MDbt

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Robbin's says that "57% of Turner's is due to nondisjunction, 30% to mosaicism and 14% to other X chromosome abnormalities. However, studies suggest that with the use of more sensitive techniques such as FISH and PCR, and the analysis of more than one cell type (blood and fibroblast) mosaicism increases to 75%"
 

Docster

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Robbin's says that "57% of Turner's is due to nondisjunction, 30% to mosaicism and 14% to other X chromosome abnormalities. However, studies suggest that with the use of more sensitive techniques such as FISH and PCR, and the analysis of more than one cell type (blood and fibroblast) mosaicism increases to 75%"
we were taught in class that many previously thought non-disjunction cases of turner's have turned out to really be mosaicism when analyzed by FISH.

so, good 'ol Robbins and UWorld are right on.
 

Oh_Gee

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Robbin's says that "57% of Turner's is due to nondisjunction, 30% to mosaicism and 14% to other X chromosome abnormalities. However, studies suggest that with the use of more sensitive techniques such as FISH and PCR, and the analysis of more than one cell type (blood and fibroblast) mosaicism increases to 75%"
what edition of robbins says the part i bolded? i have the 9th edition and i see the part where it talks about the 57% on page 166 but not the bolded part