Elias Gatos, M.D.
Surgeon Gynecologist – Obstetrician
Scientific Director emBIO Assisted Reproduction Unit

Fluorescence In Situ Hybridization (FISH)

What it is
It is an analysis method including the use of special colorants targeting specific chromosomes. The fluorescence in situ hybridisation is a popular technique to determine the gender, diagnose gender-related conditions at the “X” chromosome (diseases caused from abnormal X chromosome genes largely associated with the X chromosome are called X diseases such as hemophilia, chromosomal aneuploidies and translocations, as well as chromosomal anomalies such as trisomies and monosomies (Down syndrome –trisomy 21, Edwards syndrome –trisomy 18, Kleinefelter, Turner sundrome etc.)…

When to recommend it
Some couples carry genetic diseases: b-thalassaemia, sickle cell anaemia, type A hemophilia, cystic fibrosis, and Gravis myasthenia.
For example, in cases where either parent has an abnormal gene in the X chromosome, their male offspring will be severely affected by this abnormal gene and have the disease, whereas female children will not be affected since they have an additional backup X chromosome.

There are also genetic diseases occurring as anomalies to an entire chromosome, such as Down syndrome –patients have the 21st chromosome three times- and other genetic diseases are caused when a single small gene is absent (e.g. cystic fibrosis).

When the sperm has more or less chromosomes than the normal 23 chromosomes (aneuploidy), then if the egg is fertilised, a chromosomally abnormal embryo will be created having excess and/or loss of genetic material.
Moreover, it has been proved that approximately 40% of egg cells coming from women over 40 are aneuploidic.

Diagnosis and success rates
The FISH method is a fast and popular method to diagnose these conditions. This way the transfer of embryos having a normal karyotype may be ensured.


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