PGD for structural chromosomal abnormalities
1. Presentation. What is it? It's a procedure that allows us to detect chromosomal imbalances in the embryos from patients who are carriers of structural chromosomal alterations such as translocations (Robertsonian and reciprocal) and inversions (pericentric and paracentric). 2. Objective. What is it used for? It allows the selection of embryos that are chromosomally normal or balanced from the embryos produced from a couple in which one of the two members is a carrier of a balanced structural chromosome abnormality. 3. Recommendations. Who and what is it for? Even though the carriers of balanced structural chromosome abnormalities don't present pathologies they can have a high risk of infertility, suffer from spontaneous abortion or have offspring with genetic imbalances resulting in pathology. Selecting embryos that are chromosomally normal in these patients decreases the risk of parents having genetically an unbalanced offspring or spontaneous abortion and increases global reproductive success. 4. Samples. How? The samples for analysis can be embryonic cells or a fraction of trophoectoderm, obtained by embryo biopsy on day 3 and day 5 of embryo development respectively. 5. Methodology Depending on the type of alteration and size of the chromosomal fragments involved in the alteration we can use the following techniques: 5.1. "Fluorescent in situ Hybridization" (FISH) Requires the hybridization of the nucleus of one or two embryonic cells with DNA probes marked with fluorescent molecules. This allows the number of copies of the chromosomal fragments implicated in the alteration to be determined. These blastomeres are obtained by biopsy and are fixed on a slide. The probes selected for the analysis depend on the alteration which one wishes to detect, thus requiring a previous personalized study. This study is performed on lymphocytes from the alteration carrier and permits the design of a personalized protocol with the selection of DNA probes. These allow chromosome imbalances that may be implicated from family histories to be discounted (this is called a "Previous Translocation Study"). 5.2. CGH arrays (aCGH) Consist of extracting and amplifying the DNA from a single blastomere or a few trophoectoderm cells collected from a biopsy into a microtube. After amplification of the representative DNA from each embryo and adult control DNA they are both marked with different fluorochromes (Cy3 y Cy5). The marked DNA is then hybridized with the 24sure+TM DNA micro‐arrays. The images are obtained and analyzed with the BlueFuse Multi 2.6 software. www.igenomix.com Before starting each treatment you must consult the laboratory in order to decide which methodology would be the most appropriate in your case. For Robertsonian translocations we recommend the CGH array technique which allows the elimination of translocations and aneuploidies in all of the chromosomes. For other structural alterations, FISH specific to the chromosomes implicated in the alteration can be performed, but in cases where there is a risk that medium or large sized unbalanced translocations may have occurred in the chromosomal fragments, CGH arrays may also be chosen as a helpful technique. 6. Sample processing and results delivery. When? The sample is transported in a special, cold and well protected container in order to avoid damage. The sample must be sent immediately to this delivery address: IGENOMIX S.L Laboratorio DGP monogénicas & diagnóstico molecular Parc Cientific Universitat de Valencia, C/ Catedrático Agustín Escardino nº9 46980 Paterna Valencia The laboratory protocol requires 24‐48h in order to perform the analysis and produce the results report. 7. How to start? Get in contact with [email protected] 8. FAQs What is the embryo biopsy? Does the embryo suffer any damage? The embryo biopsy consists of the extraction of one or a few embryo cells, (depending on their state of development). It is an invasive method and it requires the embryologist who manipulates the embryos to have a great deal of experience and ability. If the embryo is manipulated correctly the embryo develops normally after the embryo biopsy, implants properly, and results in a healthy newborn. The studies published so far, which compare children that come from biopsied embryos to those from non‐biopsied embryos, show equivalent results in clinical terms. Is it recommended that I do the biopsy on day 3 or day 5? While in many assisted reproduction centers the best diagnostic results are obtained following embryo biopsy on day 5 of development, (which means that embryo freezing or transfer on day 6 of development is obligatory), in our center we have compared diagnostic results on day 3 and day 5 of development and have found that they are equally robust on both days. The advantage of performing the biopsy on day 3 of development is that it is that embryo freezing or delaying embryo transfer is not necessary. If I do a PGD analysis for structural chromosomal alterations, am I guaranteed the gestation of a child free from the genetic anomaly which either I or my partner carries? The analysis guarantees the transfer of an embryo free from the genetic anomaly or an embryo with the anomaly balanced in the same way as the original carrier. In both these cases the embryo will be free from the original alteration pathology; however it is not possible to distinguish between normal embryos and balanced embryos. What is the difference between 24 sure Arrays and FISH? With the 24 sure+ Array technique all 24 chromosomes are studied while the FISH technique can only analyze the chromosomes implicated in the concrete chromosomal alteration searched for. However, it is not always possible to choose the technique employed for the analysis because this depends on whether the size of the fragments implicated in the chromosomal anomaly are superior to the limit of array resolution. If I perform an aneuploidy study, is it recommended that I perform a prenatal study? Even though aneuploidy screening is an extremely precise technique it is not completely free of errors inherent to the technique or the biological material which is the object of the study. Given that the chromosomal analysis is performed on a single cell, it cannot exclude embryonic mosaicism. Therefore, it is recommended that you should perform prenatal testing by amniocentesis or chorionic villus sampling. www.igenomix.com