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What is chromosomal mosaicism in IVF?



Chromosomal Mosaicism in IVF


What is ‘chromosomal mosaicism’ and why is it important for IVF?


‘Chromosomal mosaicism’ refers to the presence of more than one cell line within the body.


You are a mosaic with respect to your chromosomes if you have had a karyotype in which two or more cell lines have been noted (such as mos (45, X0; 47, XYY) or mos (46, XY; 47, XY + 21).


Chromosomal mosaicism stems from the unequal separation of sister chromatids during fetal life, leading to some cells containing extra chromosomes, and others lacking the same chromosome.


What does chromosomal mosaicism mean for me?


If you have been diagnosed as a chromosomal mosaic, you can have a perfectly healthy life, but you may have problems when you decide to have children. In fact,the reason you had a chromosomal analysis is almost certainly because your clinical infertility specialist recommended as part of your infertility diagnosis.


The level of chromosomal mosaicism in the blood should, but does not necessarily reflect the levels of mosaicism in the reproductive organs. This means that if you have 5% mosaicism in the blood for chromosome 21, you may still have 50% mosaicism in the reproductive tissues.


Why is this important? because you may be at risk of passing on genetic disease to your offspring.


Take this example, a cell with 3 copies of chromosome 21 can become two daughter cells with one containg a single 21 and one containing two 21′s. If this cell forms a spermatozoa or egg, the embryo will have three copies of chromosome 21 (Downs syndome).


So, it is advisable always to have a karyotype performed before considering having children.


What can I do if I am diagnosed with chromosomal mosaicism?

If your chromosome analysis does reveal the presence of mosaicism, your best course of action is to seek advice from a clinical geneticist. The best course of treatment for you is probably preimplantation genetic diagnosis.

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