Dr. Laila Bastaki, MD
Consultant of Medical Genetics
Director of KMGC

(PGD)
PGD is a state-of-the-art procedure used in conjunction with In Vitro
Fertilization (IVF) in which the embryo is tested for certain conditions prior to being placed in the womb of the woman.
PGD was first reported in
1990.
PGD combines the recent advances in molecular genetics and in assisted reproductive technology

2.
3.
4.
1.
Chromosomal Disorders
Numerical
Chromosomal aneuploidy
Structural
Inversions
Translocations
Deletions and duplications
Gender determination for severe Xlinked diseases with unknown gene
Severe monogenic diseases (cystic fibrosis, ß thalassaemia, sickle cell anemia, fragile X syndrome, myopathies)
PGD for HLA-typing (to allow selection of embryos that are histocompatible with live siblings)

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Technically demanding
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Very Complex
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Requires special skills

Ovarian Stimulation
IVF
Blastomere Biopsy on Day 3
Outcome
Clinically Normal Baby
Transfer of
Unaffected Embryo
Genetic Analysis
(FISH or
Molecular)

The Methods of Preimplantation Genetic
Diagnosis
1. Remove a single cell from the 6-8-cell embryo using a fine glass needle to puncture the zona pellucida and aspirate the cell
- In skilled hands, this generally does not harm the developing embryo.
- Each cell is called a blastomere.

Fluorescence In Situ
Hybridization
(FISH).
Gene Chip array
Polymerase Chain
Reaction (PCR)

Fluorescence In Situ Hybridization (FISH)
• Using fluorescent probes specific for each chromosome.
• useful for identifying aneuploidies (incorrect chromosome numbers) and translocations
• procedure destroys the tested cell
• limited number of chromosomes can be checked simultaneously
• some abnormalities undetectable

Screening aneuploids with multiple probes

Gene chip array
(Array CGH Analysis)

What is array-CGH analysis?

Array-CGH allows the laboratory to determine if the correct number of each chromosome is present in the egg or embryo

This technology simultaneously tests for all 24 chromosomes (1-22, X and Y)

What is array-CGH analysis?

With array-CGH, the amount of DNA present for each chromosome is compared to that of a normal standard, enabling us to detect monosomies (missing chromosomes), trisomies (extra chromosomes), and other abnormalities

What is array-CGH analysis?

Genetic testing for specific disease loci (PCR)
Polymerase chain reaction (PCR)
-The gene causing the disorder should be confirmed and tested in the couple
-Amplification of DNA specific to a gene of interest (family history guides choice of genes)
-Second round PCR used for specific exonic sequencing and/or linkage analysis (Fragment analysis)

Examples of genetic disorders detectable via PCR-based tests:
- Tay Sachs (autosomal recessive)
- Cystic fibrosis (autosomal recessive)
- Huntington’s disease (autosomal dominant)
- Thalassemias (autosomal recessive blood disorder)
- Duchenne muscular dystrophy (X-linked recessive)
- Spinal muscular atrophy (X-linked recessive)
As more genetic tests are developed as diagnostic tools, more will be used for predictive purposes in PDG.

Limitations of PCR-based tests:
• Both alleles may not amplify equally (allele dropout), leading to misdiagnosis or inconclusive results
• PCR-based tests only detect disorders at target loci; other mutations may exist elsewhere
• To accommodate these limitations, prenatal amniocentesis or chorionic villus sampling is usually recommended as a supplement to PGD.

Reduction in the
Chance of Having a
Child with Aneuploidy
Reduces the possibility of pregnancy termination following a prenatal diagnosis of a genetic disorder.

Embryo damage
Oocyte and Embryo Biopsy are invasive procedures
Misdiagnosis The accuracy of the PGD for translocation is 90%.
False negative result
False positive result
The chance for NO result
The chance for mosaicism
IVF Risks
Not Achieving Pregnancy
There may not be any normal embryos available for transfer.
The embryos may not implant and develop even if they do not have the defect.
The workup for PGD is expensive and labor intensive
PGD can only detect a specific genetic disease in an embryo. It cannot detect many genetic disorders at a time and cannot guarantee that the fetus will not have an unrelated birth defect.

Human Error
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Mislabeling, misidentification, misinterpretation
Wrong embryo transfer
Incorrect probes or primers
Technical
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Probe or primer failure
Contamination (maternal, paternal, operator, carry-over)
Intrinsic (embryo)
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Mosaicism
Allele drop out
Uniparental Disomy

European Society of Human Reproduction and
Embryology (ESHRE) PGD Consortium, 2003
Major malformations: 2.6%
Phocomelia and pulmonary deficiency, chylothorax, congenital hip dislocation, abdominal cystic mass, pes equinivarus, exencephaly
Minor malformations: 1.4% syndactyly, hydrocele testis, ASD, mongolian spot, sacral dimple
Liebaers et al, Belgium 2010
Major malformations: 2.1% vs ICSI: 3.4% chylothorax, VSD, oeasophageal atresia, cataract, umbilical hernia, ichthyosis, cardiopathy

Conceive naturally and have prenatal diagnosis during pregnancy

Efforts continue to be focused on improving methods to obtain an accurate diagnosis.
PGD holds great promise for the future as techniques and genetic tests are perfected.
PGD may become routine in the next few years.

For couples at risk for producing offspring with either debilitating monogenic disorders or chromosomal abnormalities
IVF/PGD represents a major scientific advance

Complications, both before and after birth, are no different in type or number from those found in a comparable ICSI population
Other parameters such as birth weight and length, are also similar to an ICSI population
PGD appears to be a safe method to avoid the birth of children with genetic defects

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Before PGD is performed, genetic counseling must be provided to ensure that patients fully understand the
 risk for having an affected child
 the impact of the disease
 the available options
 the multiple technical limitations including the possibility of an erroneous result
Prenatal diagnostic testing is strongly encouraged to confirm the results of PGD