Embryonic genetic diagnosis

Preimplantation Genetic Diagnosis (PGD) is a technique for diagnosing genetic abnormalities in embryos during in vitro fertilization (IVF). Similar to Embryonic Biology Testing (PGT), PGD aims to screen for specific genetic diseases or chromosomal abnormalities and select healthy embryos for transplantation to reduce the risk of transmitting genetic diseases to offspring. The following is a detailed explanation of PGD:

1. Target audience: PGD is suitable for couples who are known to carry genetic diseases, where one or both individuals carry specific genetic mutations or chromosomal abnormalities. These genetic diseases can be monogenic, such as cystic fibrosis, thalassemia, etc., or they can be chromosomal abnormalities, such as chromosomal rearrangements, chromosomal deletions, etc.

2. Process: The PGD process is combined with IVF. Firstly, using superovulation drugs to promote the production of multiple eggs in women. Then, sperm and egg are fertilized in vitro to form multiple fertilized eggs. At the 6-8 cell stage of embryonic development, one or more cells in the embryo are sampled. The sampled cells will undergo genetic analysis to determine the presence of specific genetic diseases or chromosomal abnormalities. Based on the analysis results, select healthy embryos for transplantation into the mother's uterus.

3. Genetic analysis: PGD uses various genetic techniques for analysis to detect whether the embryo carries specific genetic mutations or chromosomal abnormalities. Common analysis methods include polymerase chain reaction (PCR), fluorescence in situ hybridization (FISH), whole genome amplification (WGA), and gene sequencing. The specific analysis method depends on the genetic disease or chromosomal abnormalities that need to be detected.

4. Ethical and legal issues: PGD involves genetic screening and selection of embryos, thus involving some ethical and legal issues. This includes ethical issues related to selective screening, screening, and disposal of embryos. The use and restrictions of PGD vary in different countries and regions. Before undergoing PGD, it is recommended to consult a doctor and genetic counselor to understand local regulations and ethical guidelines.

It should be noted that PGD is not 100% accurate and there is still a certain misdiagnosis rate. Furthermore, PGD does not guarantee successful pregnancy or the birth of a healthy baby. Before undergoing PGD, detailed consultation and discussion with doctors and genetic counselors should be conducted to understand its applicability, advantages, limitations, and risks. In addition, PGD requires highly professional laboratory facilities and experienced teams to execute and interpret the results.

PGD usually uses the following common analysis methods for detecting chromosomal abnormalities:

1. Fluorescence in situ hybridization (FISH): FISH is a commonly used molecular genetic technique that can be used to detect chromosomal structural and numerical abnormalities. It uses fluorescent probes to label specific chromosomal regions or numbers, and then observes the presence or absence of fluorescent signals through a microscope to determine chromosomal abnormalities. FISH can be performed quickly and has high accuracy for some common chromosomal abnormalities, such as trisomy syndrome (such as Down syndrome).

2. Whole genome amplification (WGA): WGA is a technique that amplifies the limited DNA of embryonic cells to a sufficient amount for genetic analysis. WGA can be achieved using various methods, such as PCR (polymerase chain reaction) or multi site amplification (MLPA). Through WGA, sufficient DNA can be obtained for subsequent chromosomal anomaly detection, such as chromosomal number and structural abnormalities.

3. Digital PCR: Digital PCR is a highly sensitive PCR technique that can be used to detect chromosomal abnormalities and partial chromosomal deletions. It can achieve precise counting of target sequences by dispersing DNA molecules into many small reaction regions, each with only one or zero DNA molecules. Digital PCR has high accuracy and sensitivity in detecting chromosomal abnormalities.

4. Next Generation Sequencing (NGS): NGS is an efficient gene sequencing technique that can be used to detect chromosomal number abnormalities, structural abnormalities, and chromosomal rearrangements. By sequencing the DNA of embryos, detailed genetic information can be obtained and accurate analysis of chromosomal abnormalities can be performed. The application of NGS in PGD is constantly developing, with high resolution and comprehensive genetic information.

These methods are typically used in conjunction with the PGD process to screen and analyze chromosomal abnormalities in embryos. The specific method used depends on the laboratory's technology and equipment, as well as the types of chromosomal abnormalities that need to be detected. In the PGD process, professional laboratories and experienced teams will choose the most suitable analytical method based on specific situations, and ensure the accuracy and reliability of the results.