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bingcentipede
"Unbalanced chromosome rearrangement" is also a description of trisomy in and of itself
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bingcentipede
"Unbalanced chromosome rearrangement" is also a description of trisomy in and of itself
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nbmeanswersownersucks
I think it's more because a spontaneous microdeletion would not really explain the previous lost pregnancies whereas an unbalanced translocation in the mom could. And I think it could be any of the big trisomies (13, 18, 21) but 21 is most common.
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m0niagui
so, it is the mother that has Down's Sd?
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jj375
No, the mother doesnt have down syndrome. As far as I know, the mother has a BALANCED translocation - for example (totally made the chromosome # up) she may have a piece of chrom 11 and chrom 4 swap places. However they are balanced since they are both there, no genetic material is missing os she looks healthy and is fine. BUT when her eggs are made, some eggs may get the chrom 11 (+ piece of chrom 4) and then her regular copy of chrom 4...Now that baby also gets a chromosome 4 from the dad. The baby will end up with 3 copies of part of chrom 4 but 1 part of chrom 11! So the kid is unbalanced and may die in utero (spontaneous abortions). I hope that was clear Here is a photo that may help: https://accessmedicine.mhmedical.com/data/books/hoff2/hoff2_c006f005.png
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chaosawaits
I think the point is that no matter which disease you think it is, whether trisomy 13, 18, 21 or even Turner syndrome, in all those genetic disorders, the most common cause is an unbalanced chromosome rearrangement. I don't think you're actually supposed to know the disease.
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an1
@chaosawaits The MCC is not actually unbalanced chromosomes (robertsonian ~ 4%). the most common is nondisjunction (~95%). also a point from UW was that robertsonian defects will often have a family hx of recurrent miscarriages. we don't have a fam hx of this woman but she herself has a hx which could also help us diagnose. and secondly, gonadal mosaicism could have been ruled out easily because gonadal is fatal, only somatic can result in survival!
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submitted by โutap2001(27)
There are three types of Down syndrome: trisomy 21 (nondisjunction), translocation and mosaicism.
Trisomy 21, the most common type of Down syndrome, occurs when there are three, rather than two, number 21 chromosomes present in every cell of the body. Instead of the usual 46 chromosomes, a person with Down syndrome has 47. It is this additional genetic material that alters the course of development and causes the characteristics associated with the syndrome. Trisomy 21 accounts for 95% of cases.
Translocation accounts for 4% of all cases of Down syndrome. In translocation, part of chromosome 21 breaks off during cell division and attaches to another chromosome, typically chromosome 14. While the total number of chromosomes in the cells remain 46, the presence of an extra part of chromosome 21 causes the characteristics of Down syndrome.
Mosaicism occurs when nondisjunction of chromosome 21 takes place in one โ but not all โ of the initial cell divisions after fertilization.When this occurs, there is a mixture of two types of cells, some containing the usual 46 chromosomes and others containing 47. Mosaicism accounts for about 1% of all cases of Down syndrome.
Uworld genetic section has similar question.