The passing on of genetic diseases from parents to children has always been a serious problem. Since 1990, it has been possible to do genetic testing on embryos before implantation in the uterus of the woman who wants to have a child. The method is called Preimplantation Genetic Diagnosis and is now a powerful tool for couples facing the increased likelihood of passing on a genetic disease to their children. Thousands of healthy children have been born worldwide due to the availability of this method.
Preimplantation genetic diagnosis is divided into two categories:
• diagnosed genetic diseases
• testing associated with chromosomal changes
Since it has been possible to diagnose genetic diseases, couples where each partner has a specific genetic disease can benefit (e.g., Type a and b Thalassaemia).
Screening for chromosomal alterations relates to numerical chromosome changes and structural abnormalities. This is a very important test, since it is known that the chances for chromosomal changes (e.g. Down’s Syndrome) increase with the woman’s age.
However, there are cases where changes in chromosome structure (inversion or translocation of chromosome material) do not depend on age. There are rare cases of couples where one or both partners contribute a chromosomal change (not necessarily the same). This change, may lead to recurrent miscarriages or repeated unsuccessful IVF attempts.
Preimplantation Genetic Diagnosis has been applied clinically in Greece and abroad for several years with very good results. Experience has shown that a successful programme of Preimplantation Genetic Diagnosis requires the harmonious cooperation of many specialties, such as doctors, clinical embryologists, psychologists and geneticists. At the same time, genetic counselling provided to the couple by specialists plays a particularly important role.
The contribution of genetic counselling, research and clinical documentation is considered indispensable in assisted reproductive technology and can demonstrably and accurately identify the probability of a couple having a healthy child using the process of pre-implantation genetic diagnosis. It is noteworthy that genetic counselling services are only provided in a few IVF units in Greece and Europe.
Characteristically, according to Embryolab’s study results, when pre-implantation diagnosis was applied in advance to check for aneuploidy, the birth rate for healthy children doubled compared to the international literature for the older women group (> 35) and overburdened medical profile of the women – e.g. history of a series of miscarriages- presenting the highest chances of chromosomal changes in embryos. Furthermore, the data from this study showed that 1 in 2 couples would be delivering a healthy child after checking via pre-implantation diagnosis for hereditary diseases, including monogenic diseases such as thalassaemia and cystic fibrosis. It is important to note that this diagnosis is mainly seen at a younger age (<35), where the objective is to check embryos for hereditary diseases, and will not necessarily identify existing problems.
Advantages of implantation diagnosis: it is a painless procedure for the couple and helps avoid potential therapeutic scraping in advanced stages of pregnancy, if the diagnosis is positive for a particular disease. A very early diagnosis systems like PGD is way ahead of prenatal checks (amniocentesis or trophoblast biopsy).
The table below presents an indicative list of genetic diseases and chromosomal changes identifiable through PGD
|GENETIC DISEASE||CHROMOSOMAL CHANGES|
|Type a and b Thalassaemia||Down’s Syndrome (Trisomy 21)|
|Sickle cell anaemia||Edwards Syndrome (Trisomy 18)|
|Cystic fibrosis||Patau Syndrome (Trisomy 13)|
|Tay-Sachs Syndrome||Turner Syndrome (X0)|
|Huntington’s disease||Klinerfelter Syndrome (XXY)|
|Muscular Dystrophy Duchene/ Becker|
|Wilson’s disease (hepatolenticular degeneration)|
|Spinal muscular atrophy|
|Prader Willy Syndrome|
|Fragile X Syndrome|
|Y chromosome microdeletion|
The development of specific methods improves the rate of correct diagnosis and expands the list of genetic diseases for which genetic testing can be provided.
Achievements in this area are continuing. As the list increases in terms of diseases for which checking is possible, there is hope for the prompt elimination of genetic diseases.