Preimplantation Genetic Diagnosis (PGD)
WHAT IS PREIMPLANTATION GENETIC DIAGNOSIS?
Preimplantation Genetic Diagnosis is a technique used to detect genetic abnormalities in embryos. It is an alternative solution to the methods of prenatal diagnosis (either with CVS or amniocentesis) for couples at risk of transmitting a hereditary disease to their children. During prenatal diagnosis if it is found that the pregnant fetus is infected with a genetic disease, the couple will have to decide whether they wish to continue pregnancy or to terminate it.
Preimplantation genetic diagnosis combined with IVF allows fertile and sub-fertile couples to have a healthy child without going through the possibility of stopping a pregnancy.
WHICH PATIENTS BENEFIT FROM THE TEST?
Preimplantation genetic diagnosis can benefit every couple with an increased risk of inheriting a genetic disorder or condition to their baby. It is also applied to IVF couples undergoing PGS in order to increase the probability of pregnancy, by selecting non-aneuploid embryos.
WHICH DISEASES CAN BE DIAGNOSED WITH THIS TEST?
- A monogenic disorder: Where one or two parents are carriers of a genetic disease, e.g. Mediterranean anemia
– A known chromosomal disorder: In terms of numerical abnormalities and structural chromosome alterations.
– A serious sex-linked condition: Such as Duchenne Muscular Dystrophy, Haemophilia A & B and Fragile X Syndrome
HOW IS PREIMPLANTATION GENETIC DIAGNOSIS APPLIED?
It begins with the normal process of IVF involving ovarian stimulation, egg collection, sperm recovery and fertilization in the laboratory. PGD involves the removal of a single cell from the fetus and its genetic diagnosis. One or two blastomeres are carefully removed after opening the ovule’s transparent zone, without causing any damage to the future development of the embryo.
THE GENETIC DIAGNOSIS
Genetic diagnosis is done with various techniques, based on the disease to be avoided.
– Comparative genomic hybridization in oligonucleotide microarray – array cgh Identifies chromosomal deficits and doubling by checking all the chromosomes of the genetic material of each embryo.
– Polymerase chain reaction
It isused for molecular diagnosis. In each case the test is personalized depending on the gene and the disease.
– Fluorescence in situ hybridization (FISH)
It is used for cytogenetic diagnosis, i.e. chromosome analysis to avoid numerical or structural anomalies.
CONCERNS AND DISADVANTAGES
Reimplantation Genetic Diagnosis may seem to be the ideal choice for patients who have a genetic or chromosomal disease, but it has some concerns and disadvantages:
• Around 10 embryos are required for Preimplantation Genetic Diagnosis to be successful so that after the process, some healthy embryos are available for transport. In some cases, all embryos may be unhealthy.
• An incorrect diagnosis can occur by single cell analysis which has limitations. Therefore, prenatal diagnosis is still recommended to confirm the status of the embryo.
• Unfortunately, not all chromosomal or genetic abnormalities can be diagnosed with Preimplantation Genetic Diagnosis.
• It is possible that technical problems can occur during biopsy.
• Pregnancy is not guaranteed after transfer even with successful IVF and Preimplantation Genetic Diagnosis,
• Patients should undergo IVF, and this can be difficult and stressful.