Pre-implantation Genetic Diagnosis

dna

GENERA is the leading Italian center in the study and diagnosis of genetic diseases and chromosomal abnormalities in the embryo, also due to the collaboration with the laboratory GENETYX.
The procedure is called Preimplantation Genetic Diagnosis (PGD/PGD-A) and requires an IVF cycle to be carried out.

Hereafter the most common questions to understand these techniques that offer better prospects for couples to achieve our common goal: childbirth.

For more information on PGD and PGD-A techniques and to know the results obtained at GENERA laboratories, please consult the page PGD/PGS – Preimplantation Genetic Diagnosis

 

WHAT IS PRE-IMPLANTATION GENETIC DIAGNOSIS OR PGD?

Pre-implantation Genetic Diagnosis (PGD) is a technique designed to identify and transfer embryos not suffering from an inheritable disease in couples at high reproductive risk among those ones produced in an IVF cycle.

Are there risks for embryos undergoing PGD?

PGD is a safe procedure for the embryo, which is performed before its putative implantation in the uterus and that allows the identification of mutations predisposing to inheritable monogenic diseases at a very early stage of development, namely 5 to 7 days after fertilization (or blastocyst stage). At this stage the blastocyst has already differentiated in the embryonic portion (Inner Cells Mass, ICM) and the extra-embryonic portion (Trophectoderm, TE). The biopsy of a few cells of the trophectoderm (<5 % of its biomass) has proven to be safe and does not compromise embryo’s development and implantation potential.

What is the aim of PGD?

The aim is to prevent a couple from conceiving a child specifically and exclusively affected by a pathology whose causative mutation is present in the parental karyotypes.

A preliminary work-up is needed to build the specific probes needed for the analysis.

Which are the diseases that can be diagnosed with PGD?

Cystic fibrosis, thalassemia, spinal muscular atrophy, myotonic dystrophy, neurofibromatosis, Duchenne and Becker muscular dystrophy, hemophilia A or B, and fragile X syndrome are just some of the more than 10,000 genetic diseases that, according to the World Health Organization (WHO), is possible to diagnose through PGD.

Over 95% of these pathologies do not have a specific cure and, despite being very rare taken individually, they have a total estimated prevalence of about 1% in the general population. Every person is on average a healthy and generally asymptomatic carrier of about 2.8 genetic mutations and, often, when two carriers of the same mutation meet—something that is more frequent in the islands—the children who are born can be affected by congenital diseases, early mortality, mental retardation and/or permanent disability.

Where is PGD available?

For couples interested in PGD, the first step is a preliminary interview with a specialist in medical genetics, who, after having assessed the couple’s clinical history, will explain the procedures, the possibilities and limitations of diagnosis, success rates, and risks related to treatment. Couples who are referred to a specialist have the opportunity to have an accurate picture of what could be their path in case they decide to undergo an IVF cycle. A peripheral blood sampling from the couple and, if possible, a buccal swab from some of the couple’s family members will be necessary and sufficient for the genetic team to build the molecular probes for PGD. Then, a gynecologist expert of Reproductive Medicine will allow the couple to start the IVF treatment. Following the IVF treatment, a number of embryos will be produced. An embryo biopsy will be carried out at the blastocyst stage (day 5 to 7 of in-vitro pre-implantation development). The biopsy consists in the removal of a fragment belonging to the extra-embryonic portion of the blastocyst that originates only the embryonic annexes (such as the placenta, the amniotic sac, etc.).

This portion of the embryo has the same karyotype as the ICM from which the fetus originates. The genetic analysis carried out on the collected cells is therefore sufficient to diagnose whether an embryo is affected, healthy carrier or not affected by a specific genetic disease. Furthermore, there is no risk associated with the procedure for the embryos when the biopsy is carried out at the blastocyst stage. Therefore, the implantation rate following the transfer of embryos that are not affected or are healthy carriers of a monogenic disease is identical to that of patients of the same age who undergo an IVF cycle without PGD.

WHAT IS PGS OR PRE-IMPLANTATION ANEUPLOIDY SCREENING?

 

There is also a form of PGD aimed solely at improving the clinical efficiency of IVF, known as pre-implantation genetic diagnosis for aneuploidy testing (PGD-A or PGS).

This technique has been designed to identify and transfer the blastocysts with a normal chromosomal constitution from a cohort of embryos produced by a couple during an IVF cycle. It aims at increasing the efficiency of each single treatment and minimize the risks related with human reproduction. The occurrence of chromosomal abnormalities is a de novo event, i.e., not strictly hereditary but developed during oocyte/sperm maturation. Specifically, the probability of their occurrence in humans is strictly proportional to woman’s reproductive age.

 

Which are the goals of PGS?

The goals of PGS are: to decrease the miscarriage rate (which is reduced to less than 1/4 compared to patients of the same age who undergo a standard IVF cycle), to increase the term pregnancy rate per embryo transfer (which increases on average up to 50% for each transferred embryo across the border of female age), as well as to prevent the conception of children affected by chromosomal pathologies, such as the Down syndrome (trisomy of chromosome 21).

PGS is therefore a safe and reliable diagnostic method currently available to increase the success rate per transfer while sharply reducing the risk of miscarriage. By avoiding inefficient embryo transfers, which are potentially risky for a woman from both a physical and psychological point of view, PGS is a strategy with a very high potential that is increasingly adopted in the clinical practice worldwide.

This analysis also does not require a preliminary work-up and the method of analysis is common to all patients who request it.

 

When is PGS recommended?

This type of diagnosis is indicated for women older than 35 (the average age of women who undergo IVF is 36 years, and the 30% of them are over 40), an age after which there is significant increase in the prevalence of chromosomal abnormalities in the embryos. In fact, at the age of 27, about 1 pregnancy out of every 450 results in a child with chromosomal abnormalities, at 35 years it is about 1 out of every 300 pregnancies, then 1 out of every 60 for women aged 40 and finally an alarming 1 out of every 20 pregnancies at the age of 45 (source: www.syndrome-down.it).

PGS is also indicated for couples with a history of miscarriage and recurrent implantation failures in IVF. The risk of miscarriage in women with a mean age of over 36 years is reduced to less than 10% per conception due to this technique.

 

Is PGS also important to reduce the risk of twins and multiple births?

According to the analysis carried out by the IVF Registry of the Italian National Institute of Health on IVF cycles, the rate of miscarriage after IVF at an average age of 36.3 years is 21.1% and reaches peaks of more than 51% in women older than 42, while the rate of twin pregnancies is 20.2% and that of triplets and quadruplets is 2.3%.
The identification of embryos with a correct number of chromosomes (euploid) makes it possible to eliminate the genetic contribution to implantation failure. Therefore, after PGS, 50% of the euploid embryos results in a healthy full-term pregnancy regardless maternal age. This evidence allows the transfer of a single euploid embryo even in patients of advanced maternal age, reducing the risk of twins and multiple births (in a study presented by the GENERA Group it drops from 21% down to less than 7%), which has always been an important complication of IVF.
PGS, which is still intensely debated in Italy, has been widely used for a long time in the United States with astonishing results which have been confirmed by Italian and European centers that have successfully adopted it in their clinical practice.

WHICH CENTERS IN ITALY ARE EQUIPPED TO PROVIDE PRE-IMPLANTATION GENETIC DIAGNOSIS?

In 2014 only 17.7% of the IVF centers in Italy, i.e. 1 out of 5, was able to offer preimplantation genetic diagnosis to their patients. This was the result of the Italian national survey promoted by the GENERA Center, which was presented at the conference “The new era of PGS application in ART” (Rome, 13-14 February 2015).

The data in this survey were collected from 112 of the 189 IVF centers of second and third level spread throughout the country (public, private and affiliated private centers), on the basis of the possibility for couples to get access to a preimplantation genetic diagnosis (PGD/PGS) service and the number of treatments that they performed. The distribution across the country was uniform: 6 in the north, 8 in central Italy and 6 in southern Italy and major islands, for a total of 20 centers. Four centers started offering the service in 2015.

In most of the regions where this service is available, however, the number of PGD treatments performed by each center is often less than 50 cycles per year, with the exception of Sardinia (public center), Campania, Veneto and Tuscany. In these regions the number is between 50 and 100 cycles per year, but in Emilia Romagna and Lazio, where the biggest centers are located, this number rises up to about 300 and 1000, respectively. In Lombardy, so far the region where most IVF treatments are done, there are various centers that were getting ready to provide PGD starting from 2015.

WHAT ABOUT PREIMPLANTATION GENETIC DIAGNOSIS FOR FERTILE COUPLES THAT ARE CARRIERS OF MONOGENIC DISEASES? 

 

 

In 2014 in Italy about 2000 couples fertile who were carriers of a genetic disease were not able to get access to preimplantation genetic diagnosis because of the prohibition imposed by the Italian Law 40/2004 that made this technique available only to those who require IVF because of certified infertility. The law grants only sterile and infertile couples who are carriers of genetically transmissible diseases with the possibility of get access to IVF techniques with pre-implantation screening, while indirectly prohibits it for fertile carriers of hereditary diseases.

Constitutional Court Ruling No. 96/2015 overturns this prohibition

Now, instead, thanks to the regulatory intervention of the Italian Constitutional Court that on 14 May 2015 declared this specific rule contained in Law No. 40 unconstitutional, even fertile couples that are carriers of genetic abnormalities can access to IVF in to undergo preimplantation diagnosis and be informed about the state of health of their embryo(s).

This prohibition in fact overturned by the Court oversteps certain fundamental constitutional rights. More precisely:

1) The principle of equality (Article 3 of the Constitution) between those who are infertile and carriers of genetic diseases who can undergo IVF with pre-implantation genetic diagnosis and those who are fertile and carriers of genetic diseases but cannot perform these tests.

2) inalienable human rights including the right of a couple to have a healthy child and the right to self-determination in procreation choices (Article 2 of the Constitution)

3) the right to health and specifically the protection of women’s health (Article 32 of the Constitution)

4) Article 117, paragraph 1, of the Constitution in relation to Articles 8 (the right to respect for private and family life) and 14 (prohibition of discrimination) of the ECHR (European Court of Human Rights).

From the 10th of June 2015, the date of publication in the Official Journal of the Italian Republic (Special Series No. 23/2015) of Ruling 96/2015, the preimplantation genetic diagnosis is a reality for fertile couples who are carriers of hereditary diseases. Moreover, in order to access preimplantation genetic diagnosis, as laid down by the Court, all a couple needs is a medical certificate stating the risk of miscarriage as provided for by Article 6 of Law 194/78.

For more information on PGD and PGS techniques and to know the results obtained at GENERA laboratories, please consult the page PGD/PGS – Pre-Implantation Genetic Diagnosis

 

 

All diagnostic tests are carried out by the GENETYX Laboratory. For more info see the website GENETYX