26 Nov Abnormal number of chromosomes. How can we prevent them?
An abnormal number of chromosomes can cause spontaneous miscarriages and genetic diseases such as Down syndrome, Turner or Edwards among others. Thanks to the genetic tests that we put at your disposal in PGD Labs, it is possible to detect chromosomal anomalies in time and prevent this type of diseases in a future baby.
What are chromosomes?
DNA is a molecule present in almost all our cells that contains the information necessary for the formation, development, growth and functioning of our body. A copy of this DNA is stored in each of our cells. Each time one of these cells is divided, the DNA is organized forming structures called chromosomes. These structures are only visible through a microscope.
Humans have 23 pairs of chromosomes. That is, 46 chromosomes in total. We inherit one of the chromosomes of each pair of our mother and the other of our father. One of these pairs is responsible for determining the sex of the baby: women have two X chromosomes and men an X and Y chromosome. That is, we inherit 23 of our father’s chromosomes (found inside each sperm) and 23 chromosomes of our mother (found inside each ovule).
It’s important for us to have the correct number of chromosomes in our cells. Changes in the number of chromosomes can mean a change in the amount of genetic information (DNA) that can lead to health problems (genetic diseases). Examples of numerical chromosomal abnormalities are:
- Down syndrome. When a child is born with three chromosomes 21 instead of two.
- Turner syndrome. When a girl is born with a single X chromosome instead of two.
- Syndrome of Klinifelter. When a child is born with a Y chromosome and two X chromosomes instead of a Y chromosome and a single X chromosome.
How are these anomalies produced? Sometimes, during and in the first steps of embryo development errors can occur producing an embryo with an abnormal number or chromosomes (having an abnormal number of chromosomes, because one is missing or because there’s an extra one is called aneuploidy).
What happens if an embryo has an abnormal number of chromosomes?
Although most embryos can not survive with a missing (monosomy) or extra (trisomy) chromosome/s and are related to implantation failure or spontaneous miscarriage, some others can survive till birth leading to a genetic syndrome (for example, trisomy 21 related to Down Syndrome).
How can we avoid an abnormal number of chromosomes in the embryos during an IVF treatment?
Preimplantation Genetic Testing for aneuploidy (PGT-AS) is a genetic screening that can be performed on the embryos during an IVF treatment, before they are implanted in the womb. It allows to detect abnormalities in the number of chromosomes (aneuploidies) and transfer only the embryos that are chromosomally normal (euploid).
By screening the embryos for chromosomal aneuploidies we can help couples to:
- Increase pregnancy rate
- Decrease miscarriage rate
- Reduce the risk of having a baby with a chromosomal syndrome
Although these chromosomal abnormalities can occur naturally in any individual, some specific groups of patients are at higher risk to develop chromosomal abnormal embryos and can preferentially benefit from PGT-A:
- Infertile couples with two or more IVF cycles without pregnancy
- Couples with repeated miscarriages (with 2 or more previous miscarriages)
- Women with advanced maternal age (over 36 years old)
- Men with abnormal result in sperm FISH
- Couples with a previously affected pregnancy or baby of a chromosomal syndrome