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How does PGD-seq works?
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How does PGD-seq work?
Nowadays, next generation sequencing (NGS) is the most effective technique available for the study of the genome. For this reason, it has become an important instrument for preimplantation genetic diagnosis.
Thought PGT-A and PGT-M studies based on NGS technologies, it offers comprehensive information concerning aneuploidies, genetic mutations and unbalanced translocations in embryos; and creates a reproductive opportunity for couples who are exposed to an increased risk of having a child with a specific monogenic disorder
With PGD-SEQ panels, and applying them on DNA samples from both parents and additional family members, you will be able to detect simultaneously the point mutations, responsible of the genetic disease, and different SNPs surrounding them. The double-test study (direct and indirect) fully limits the misdiagnosis risk and safe identifies which embryos are affected, carrier or unaffected.
Steps in a PGT-M by NGS technology Study
To achieve a PGT-M study we will require to follow some steps:
1. Case Review
The family clinical report arrives at the laboratory. Couple receive appropriate genetic counselling about the disease which their families are affected, and they are on risk to transfer to their descendants.
2. Panel Design
Our support staff will receive your doubts about the patient’s disease. We will require to know the concrete mutation than affects the family and information about familiar samples available, carrier state, severity on the disease…
The PGD-SEQ panel will be designed for the mutation and family to study. Also, there are hundreds of panels ready-to-send, covering the most common genetic diseases.
3. Informative Study
You will receive documentation about how to proceed with the study. Which samples will be required, deadlines, and fully support from our staff.
In general, blood from both parents is always required, and an additional familiar sample for each mutation you want to detect. If the couple had a previous child, this sample could be used; if there are not previous child, we could use other familiar samples instead. For get more information about the samples required in each case, please check future articles in our KDB.
Genomic material will be obtained from those blood samples. Applying our PGD-SEQ kit to these samples, we will obtain the “Informativity study”. This study will allow to identify all the alleles presents on the study and their origin.
4. Embryo Biopsy
After ART cycle, the embryos should be biopsied on day 3 or 5 by an experienced embryologist. We will use this sample to analyze individually the genome on each embryo.
The biopsy will not affect the future embryo viability.
5. PGD-seq study, in 3 steps:
5.1 First Amplification
When the biopsied embryo samples arrive at the laboratory, they only include up to 10 individual cells from each biopsied embryo. So, it is required to increase the DNA amount for each sample, to allow future studies.
In this step, the whole genome is amplified. We will get thousands of random copies from the complete genome on each embryo, and the quality and amount will depend on the technique used (WGA, picoplex, etc.)
5.2. Second Amplification
From the whole genome amplification, a second (re)amplification is performed. At this moment, the amplification will not affect the whole genome, but only these regions of interest will be covered. These regions will include punctual positions, around the mutation is located, and will offer a “fingerprint” for each allele on the couple. The amplification is based on multiplex PCR.
5.3 Sequencing & Analysis
The library from the second amplification will be sequenced by NGS technology. IonTorrentTM NGS technology offers the possibility of sequencing all the interesting regions in each embryo, creating an specific “fingerprint” or “variant map”. Comparing this variants code with those obtained previously during the informativity test, using a specific software, we will be able to know which allele are present in each embryo, and discard those with the affected one.