What is Preimplantation Genetic Diagnosis (PGD) or Screening(PGS) ?
Preimplantation genetic diagnosis (PGD) refers specifically to when one or both genetic parents has a known genetic abnormality and testing is performed on an embryo to determine if it also carries a genetic abnormality.
Preimplantation genetic screening (PGS) refers to techniques where embryos from presumed chromosomally normal genetic parents are screened for aneuploidy.
This Technique was applied in :
-The successful sexing of rabbit blastocyst in1967
-and was successfully used for sex determination for patients carrying X-linked diseases in human in 1989.
Indications
• Couples with a high risk of transmitting an inherited disease, for which a genetic test exists.
• Couples who undergo IVF treatment and whose embryos are screened for chromosome abnormalities (PGS) to increase the chances of an ongoing pregnancy.
PGS
– Advanced maternal age
– Recurrent miscarriages
– Repeated implantation failures
– Severe male factors
– History of chromosomally abnormal child or pregnancy
PGD
-Structural chromosomal abnormalities
-Monogenic disease
*Autosomal recessive
*Autosomal dorminant
*family history of sex-linked diseases.
The process
• Patients undergo controlled ovarian stimulation.
• Embryos are obtained with either IVF or ICSI.
• Fertilization is assessed 16-18 hrs after.
• Embryo cleavage is recorded every 24 hrs.
• Embryo biopsy ; PB (Polar Body), day 3, blastocyst
• Embryo development assay
• Selection of healthy embryos for transfer
Techniques of PGD
• FISH (Fluorescence In- situ Hybridization).
• PCR (Polymerase Chain Reaction).
• Array-CGH (Comparative Genomic Hybridization).
