اختبار ما قبل الزرع الجيني (PGT)

Preimplantation Genetic Testing (PGT)

• PGT is a method used to detect genetic abnormalities before in vitro fertilization (IVF).
• It can be performed before or after the zygote is formed.
• PGT history includes research on animal embryos and the first human application using polar body biopsy (PHB).
• A major concern in PGT is contamination.
• Early PGT methods involved polymerase chain reaction (PCR) for Mendelian disorders.
• PGT utilizing fluorescence in situ hybridization (FISH) is used for numerical chromosomal abnormalities.
• PGT can be used for familial syndromes like Li-Fraumeni (p53) and familial adenomatous polyposis (FAP).
• PGT can also identify genes like BRCA1 associated with cancer.

Objectives of PGT

• Identify genetic disorders in embryos and parents to increase the chance of healthy offspring.
• Identify genetic problems early in the IVF process, before implantation.
• Help in couples facing infertility with an aim to avoid possible genetic disorders within the resulting offspring.

Indications for PGT

• Carriers of genetic disorders.
• Individuals with confirmed genetic disorders.
• Previous child with genetic disorders.
• Disorders like thalassemia and leukemia requiring HLA typing.
• Cancer predisposition.
• Failed IVF attempts.
• Advanced maternal age.
• Recurrent pregnancy loss (RPL).
• Unexplained infertility.

PGT Methods for Chromosomal Disorders

• Fluorescence in situ hybridization (FISH): Used for identifying numerical chromosomal abnormalities like Klinefelter syndrome or X-chromosome mosaicism.
• Comparative genomic hybridization (CGH): Used for structural chromosomal abnormalities like translocations or inversions.
• Array CGH: Used to detect structural changes and marker chromosomes including insertions.
• Gene markers can be detected with these methods to support PGT.

PGT Methods for Single-Gene Disorders

• Polymerase chain reaction (PCR): Often used in conjunction with other techniques to directly test genetic changes.
• DNA sequencing: Used to identify genetic changes in single genes.
• DNA fragment analysis: Analyzing DNA segments can help identify mutations.
• Linkage analysis: Identifying mutations linked with the same marker in families.

PGT for Disease Identification

• PGT can diagnose most genetic conditions, assuming the specific genetic issue is known in the family.
• Family-specific information is needed to determine the type of PGT approach.

PGT for HLA Typing

• PGT can be used to select embryos with the appropriate HLA (human leukocyte antigen) type in cases where a child needs a compatible donor.
• Often used in families with a child suffering from leukemia to provide a suitable tissue match.

PGT for Rh Incompatibility

• PGT can be used to identify Rh-positive or Rh-negative embryos in cases where the parents have different Rh types.
• This can aid in preventing pregnancy complications for Rh-negative mothers.

Embryo Analysis

• Embryo analysis may involve FISH to determine if embryos have the proper number of chromosomes.
• Analysis can use single-gene testing (PGT-M).
• Other tests include analyzing embryos for HLA compatibility and Rh factor.

Additional Considerations

• Specific pre-treatment protocols are needed for single-gene disorder PGT.
• Time is needed for these pre-treatments (1-2 months).
• Genetic information from parents is critical for deciding the best PGT method.