PGS

Preimplantation Genetic Screening


Preimplantation Genetic Screening (PGS) technology improves the likelihood of a successful pregnancy and birth for two distinctly different groups of patients. Couples with infertility related to recurrent miscarriage or unsuccessful IVF cycles and couples who are at risk for passing on inherited genetic disease to their offspring. Following ovarian stimulation , egg collection and fertilization, embryos are cultured for another 2 days which they usually consist of 6-8 cells. Each of these cells has complete genetic information and also each cell has the potential to continue growth to establish pregnancy. Therefore, one or two cells can be removed from an 8-cells embryo by using an embryo biopsy procedure and the embryo will continue to develop normally.

 

PGS is recommended for families with a history of a specific genetic disease. The scientists in our PGS laboratory can examine each developing embryo to identify the absence or presence of these specific genetic disorders. As a result, only those embryos free of genetic disease will be transferred to the patient’s uterus so as to increase the chance of conception and ultimately a healthy baby.

 

Single gene disorders are categorized depending upon whether the gene is located on the X chromosome, an autosome or whether the gene is dominant or recessive. These classifications include autosomal recessive, autosomal dominant and X-linked.

 

For a dominant disorder, one only needs to have the abnormal DNA sequence on one chromosome. If that mutation is passed on to the embryo, the embryo will be affected with that genetic disease. One example of an autosomal dominant disorder is Myotonic dystrophy.
 

Recessive disorders require that the mutation be present on both chromosomes of the chromosome pair. If one only has the mutation on one chromosome, the individual is normal but carries the mutation in his cells and is called a carrier. The fertilization of an egg from carrier parents may result in an embryo having the mutation on both chromosomes of the chromosome pair and the embryo therefore being affected with that genetic disease. For example, Cystic fibrosis (CF) is a common autosomal recessive genetic disorder that primarily affects the lungs of CF patients. The CF mutation affects a protein within the cell that reduces the cell's ability to function properly. This results in a build up of mucous within the lungs, lung dysfunction and possible death.

 

X-linked disorders are due to mutations of genes on the X chromosome and have different patterns of inheritance due to their transmission on a sex chromosome and whether the embryo is male or female. Examples of X-linked diseases are the Fragile X syndrome and Duchenne muscular dystrophy.

 

PGS Technologies

Fluorsecence In Situ Hybridization (FISH)

 

FISH was introduced over 20 years ago to investigate partial chromosome enumeration in embryos. Due to the low number of chromosomes that can be analysed with this approach however, FISH has proved to be of limited use. Generally, only between five and nine chromosomes can be interrogated by use of this technology.

 

Microarray Based Comparative Genomic Hybridization (aCGH)

 

Array Comparative Genomic Hybridization is a high resolution tool for detecting genome-wide aneuploidies and chromosomal aberrations. It compares the embryo’s genome against a reference genome and identifies copy number differences between the two data sets.

aCGH is able to screen for all aneuploidies in one single experiment with a protocol turn-around time suitable for PGS requirements. In addition, aCGH is able to detect aberrations smaller than chromosome or chromosome-arm aneuploidies.

 

KaryoLite™ BoBs™ 

 

KaryoLite™ BoBs™ (BACs-on-Beads) has the potential to offer a simple, easy-to-use and cost-effective screening assay that can detect aneuploidies in biopsies from both cleavage and blastocyst stage human embryos. It allows for rapid detection of copy number changes in all 24 chromosomes.

KaryoLite™ BoBs™ uses BAC-DNA clones immobilized on Luminex xMAP fluorescently coded polystyrene microsphere beads. Each bead is coupled with three different BAC-DNA clones representing the p- and q-arms of all autosomes as well as sex chromosomes. For the analysis, fluorescently labeled test and reference DNAs are individually hybridized to the beads before calculating the test versus reference ratio for each genomic location represented by the BAC clones. In this way, the aneuploidy status of all chromosomes can be assessed rapidly.

 


Diagram illustrating the bead design matrix of KaryoLite™ BoBs™.

 

 

OUR GENETICS LAB

 

 

 
CONSULTATION

Consult with Dr. Viwat

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