What are chromosomes and genes?
Each and every cell that makes up our body has in its nucleus 46 chromosomes (23 from the father and 23 from the mother). The chromosomes are made up of a substance called DNA that contains our genetic information. Said information is distributed in thousands of pieces that are known as genes. Hence there are two copies of each gene, one originating from the mother and the other from the father.
What alterations in the chromosomes and in the genes can cause diseases?
- Numerical alteration: This is an anomaly that affects the number of copies of a chromosome, in other words when instead of there being two copies of a chromosome there are three or one. The most well-known example is Down Syndrome, in which there are three copies of chromosome 21 instead of two.
- Structural alteration: This is an anomaly in the contents of a chromosome, that is to say a piece is out of place or missing.
- Monogenic diseases: These are genetic diseases caused by a fault or mutation in a single gene. Known examples of this type of disease are Cystic Fibrosis, Haemophilia, X Fragile Syndrome, Myotonic Dystrophy, and Huntington’s Disease, among others.
In the case of a pregnant woman, there are two types of diagnosis for chromosomal and genetic alterations:
- Pre-natal diagnosis (PND): Amniocentesis is the most common PND method.
- Preimplantational Genetic Diagnosis (PGD): This is an early prenatal diagnosis made on the embryo on its third day of development before being transferred to the uterus, and is therefore carried out before pregnancy has been established. PGD enables embryos that are free of the disease being studied to be transferred to the mother.
When is PGD recommended?
-Couples at risk of transmitting chromosomal alterations or monogenic diseases.
-Couples with a clinical history of repeated abortions or miscarriages.
-Implantation failure after several attempts with IVF.
-Alterations in the meiosis of the spermatozoa.
-Women of advanced age.