Preimplantation Genetic Diagnosis (PGD)
Monogenic diseases are genetic disorders caused by a single defective gene that can be inherited from parent or developed ourselves during germ line development. Monogenic diseases are major causes of various problems including birth defect, early mortality and disability and throughly effect to their family both psychological and social issues.
Preimplantation genetic diagnosis (PGD) has been developed for patients at high risk of inheriting a defected gene to their children which includes all monogenic defects (autosomal recessive, autosomal dominant and X-linked disorders). Therefore, carrier testing of parents through embryonic diagnosis for monogenic disorder before or during pregnancy can help people to have healthy children, and it is an effective way to realised reproductive health of parents to control the prevalence of monogenic disease of the next child.
- If both parents carry a mutated gene, there is a 1 in 4 chance of their child having the disease.
- Using gene disease references of known status, scientists can look at the chromosome in which the gene relies on and determine from which parental chromosome of the DNA originated.
- The examination of inherited gene, scientists can then determine whether the DNA segment inherited by each embryo and therefore whether it carries the mutated gene or a normal copy using the conventional molecular genetics techniques and sequencing mutated gene by SANGER sequencing and next generation sequencing (NGS)
- Whether or not the embryo has inherited one copy of the mutated gene as a carrier like its parents or if it has two copies of the mutated gene, that will develop the disease. No copies of the mutated gene, this embryo is likely to be unaffected and a good candidate for transfer into the women’s uterus.
Preimplantation genetic diagnosis (PGD) has been performed under the investigation of defected gene both in parent and embryo using high sensitivity, specificity and reliability of molecular genetics technologies.
These genetic information provide the direct evidence for the onset of monogenic diseases of parent and prevent the transmitting monogenic disease gene to their offspring.
Each case of PGD would be discussed and evaluated by the laboratory staffs in order to assess the case and recommend the suitable technique for the couple. There are two techniques available in our center ;
1 ) Short tendem repeat (STR) – based on linkage analysis.
This technique is using the loci-specific region on DNA as comparison between samples. STR is a microsatellite which a unit of two to thirteen nucleotides repeated hundreds of times in a row on the DNA strand are consisted. Exact number of repeating units will be measured and analyzed.
This technique is using single nucleotide polymorphisms (SNPs) as a detector. There is roughly 10 million SNPs in human genome. This technique also based on linkage analysis pattern. The advantages of this technique are it takes less time for analysis, more detector, decrease chance of allele drop out, automated and broader range of genetic disease (universal test).
Why SFC performs test on Day5/Day6 ?
Day5/Day6 embryos (Blastocyst stage) are already developed embryos so biopsy makes less harmful.
We also can get mor DNAs from Day5/Day6 biopsy and less mosaic in these Day5/Day6. Recent data proved that Day5/Day6 biopsy achieved more higher success rate than Day3 biopsy.