04-07-2013, 09:02 AM
(This post was last modified: 04-07-2013, 06:28 PM by Administrator.)
The most common cause of unsuccessful implanting embryo in the uterus and abortions in the first trimester of pregnancy are genetic anomalies. Genetic information is contained in the chromosomes.
Genomic DNA analysis includes preimplantation genetic diagnosis - PGD and preimplantation genetic screening - PGS. Basis of PGD and PGS involves genetic analysis of embryos before implantation and transferring certain "normal" embryos. The first successful application of PGD for hereditary diseases is published in 1990. For the application of PGD / PGS patients must use IVF to create embryos for in vitro analysis. For diagnosis are described three distinct developmental stages: polar corpuscles removed from the oocyte / zygote (polar body biopsy); blastomers 6-8-cell embryos, day three (cleavage stage biopsy); or biopsy blastocysts cell, 5 or 6 days develops (blastocyst biopsy).
Biopsy samples are analyzed by PCR (polymerase chain reaction) or FISH (fluorescence in situ hybridization) of relevant techniques. PCR techniques are applied for the diagnosis of specific genetic diseases, whereas the FISH technique to analyze the number of chromosomes in patients with chromosomal anomalies or for sex selection of embryos for diseases transmitted on the X-chromosome.
PGD
PGD is an important scientific advance for patients who are carriers of genetic diseases, and who are at risk for transmission of inherited diseases (haemophilia, cystic fibrosis, Fragile X, Duchenne muscular dystrophy, etc.).
Statistic shows that PGD procedures are increasing each year as a result of new and successful methods of detection of abnormal gene on one level blastomers and completing the human genome sequence. One of the techniques that have been developed recently is amplification genome. This method allows the collection of DNA from one microgram blastomers, analysis and application of whole-genome microarrays.
It is very important for the detection of chromosomal abnormalities, mutations, and aneuploidies. The indications for PGD biopsy is done on the third day of embryonic development, in one or two blastomers, and transferred to a "normal" embryo of the fifth or sixth day.
PGS
PGS, unlike PGD was developed to improve the success of IVF, especially in elderly women. Indications for PGS are: elderly patients, multiple miscarriages, repeated IVF failure and male infertility.
Concerns with PGD/PGS
The embryos could be traumatized by the biopsy procedure - particularly during cleavage stage biopsy. There is some evidence that carefully performed trophoectoderm biopsies blastocysts might not weaken the embryo at all.
As with any new technique and technology, there is a "learning curve". There could be large differences between centers performing these techniques, and even between technicians within the same IVF center.
Mosaicism can complicate matters. An embryo is a mosaic if there are 2 (or more) different chromosomal patterns in cells of that embryo. There is evidence that mosaic embryos sometimes "self-repair", or possibly designate abnormal cells preferentially to the placenta instead of the fetus. More research on mosaicism is needed.
Many people believe that because life begins at conception and that the destruction of an embryo is the destruction of a person. In some cases, a genetically defective fertilized egg will mature without the presence of disorder or disease.
Sampling of Embryonic DNA Without Biopsy
On the fifth day of developmental processes in the embryo begins to absorb liquid (endometrial gland secretions), which initially accumulates in the form of vacuoles in blastomers and soon extracellularly. In this way, it creates a cavity within the embryo - blastocists cavity and structure of the embryo at this stage is called a blastocyst developmental processes.
In a recent study published in Reproductive Biomedicine Online, a group of researchers sought to achieve diagnose of genetic disease in embryonic DNA without the use of a biopsy. They found that extracting fluid from human embryos at the blastocyst stage contains DNA from embryo. Blastocysts are embryos, which are 5 or 6 days old, and they are the last free-living stage that can be studied in the laboratory prior to transfer into the uterus. They contain between 50 and 300 cells that surround a fluid-filled cavity called the blastocoels. The scientists got the idea to the blastocyst stage liquid removed, leaving the cells intact. The analysis of this fluid have proven that it contained cell-free DNA in a sufficiently good state, enough to determine several known genes of the sex chromosomes by polymerase chain reaction (PCR).
This method removes some ethical issues that arise using PGD methods. The study above is a good start. However, it is important to consider that regardless of the outcome of these studies, we need a large number of studies.
These methods cannot identify all the genetic and chromosomal disorders. These methods are not determined at the level of gene disorders or other developmental malformations and congenital anomalies. Performing these methods in any case does not reimburse prenatal screening for congenital anomalies of development during pregnancy.
Conclusion
These procedures are used for determining the presence of a particular genetic condition in the embryo prior to implantation. In this way it is possible to determine whether it is in the process of artificial insemination to damage genetic material, a disturbance in the number of chromosomes, etc. These procedures are used to mother spared spontaneous abortions, reduce the chances of multiple birth, as well as to select out an embryo that is in the best condition, which gives a greater chance of success interventions. In addition, it is possible to test for the presence of gene alleles inherited disorders, as well as a wide range of other information.
These methods are used to determine the different genetic abnormalities, and predisposition to a variety of serious diseases, and the number of genes associated with pathological conditions that can be examined is increasing. Same as with any new technology, here is also the main problem - the problem of borders. Like everything else, these technologies should be used within the limits of the moral.
Genomic DNA analysis includes preimplantation genetic diagnosis - PGD and preimplantation genetic screening - PGS. Basis of PGD and PGS involves genetic analysis of embryos before implantation and transferring certain "normal" embryos. The first successful application of PGD for hereditary diseases is published in 1990. For the application of PGD / PGS patients must use IVF to create embryos for in vitro analysis. For diagnosis are described three distinct developmental stages: polar corpuscles removed from the oocyte / zygote (polar body biopsy); blastomers 6-8-cell embryos, day three (cleavage stage biopsy); or biopsy blastocysts cell, 5 or 6 days develops (blastocyst biopsy).
Biopsy samples are analyzed by PCR (polymerase chain reaction) or FISH (fluorescence in situ hybridization) of relevant techniques. PCR techniques are applied for the diagnosis of specific genetic diseases, whereas the FISH technique to analyze the number of chromosomes in patients with chromosomal anomalies or for sex selection of embryos for diseases transmitted on the X-chromosome.
PGD
PGD is an important scientific advance for patients who are carriers of genetic diseases, and who are at risk for transmission of inherited diseases (haemophilia, cystic fibrosis, Fragile X, Duchenne muscular dystrophy, etc.).
Statistic shows that PGD procedures are increasing each year as a result of new and successful methods of detection of abnormal gene on one level blastomers and completing the human genome sequence. One of the techniques that have been developed recently is amplification genome. This method allows the collection of DNA from one microgram blastomers, analysis and application of whole-genome microarrays.
It is very important for the detection of chromosomal abnormalities, mutations, and aneuploidies. The indications for PGD biopsy is done on the third day of embryonic development, in one or two blastomers, and transferred to a "normal" embryo of the fifth or sixth day.
PGS
PGS, unlike PGD was developed to improve the success of IVF, especially in elderly women. Indications for PGS are: elderly patients, multiple miscarriages, repeated IVF failure and male infertility.
Concerns with PGD/PGS
The embryos could be traumatized by the biopsy procedure - particularly during cleavage stage biopsy. There is some evidence that carefully performed trophoectoderm biopsies blastocysts might not weaken the embryo at all.
As with any new technique and technology, there is a "learning curve". There could be large differences between centers performing these techniques, and even between technicians within the same IVF center.
Mosaicism can complicate matters. An embryo is a mosaic if there are 2 (or more) different chromosomal patterns in cells of that embryo. There is evidence that mosaic embryos sometimes "self-repair", or possibly designate abnormal cells preferentially to the placenta instead of the fetus. More research on mosaicism is needed.
Many people believe that because life begins at conception and that the destruction of an embryo is the destruction of a person. In some cases, a genetically defective fertilized egg will mature without the presence of disorder or disease.
Sampling of Embryonic DNA Without Biopsy
On the fifth day of developmental processes in the embryo begins to absorb liquid (endometrial gland secretions), which initially accumulates in the form of vacuoles in blastomers and soon extracellularly. In this way, it creates a cavity within the embryo - blastocists cavity and structure of the embryo at this stage is called a blastocyst developmental processes.
In a recent study published in Reproductive Biomedicine Online, a group of researchers sought to achieve diagnose of genetic disease in embryonic DNA without the use of a biopsy. They found that extracting fluid from human embryos at the blastocyst stage contains DNA from embryo. Blastocysts are embryos, which are 5 or 6 days old, and they are the last free-living stage that can be studied in the laboratory prior to transfer into the uterus. They contain between 50 and 300 cells that surround a fluid-filled cavity called the blastocoels. The scientists got the idea to the blastocyst stage liquid removed, leaving the cells intact. The analysis of this fluid have proven that it contained cell-free DNA in a sufficiently good state, enough to determine several known genes of the sex chromosomes by polymerase chain reaction (PCR).
This method removes some ethical issues that arise using PGD methods. The study above is a good start. However, it is important to consider that regardless of the outcome of these studies, we need a large number of studies.
These methods cannot identify all the genetic and chromosomal disorders. These methods are not determined at the level of gene disorders or other developmental malformations and congenital anomalies. Performing these methods in any case does not reimburse prenatal screening for congenital anomalies of development during pregnancy.
Conclusion
These procedures are used for determining the presence of a particular genetic condition in the embryo prior to implantation. In this way it is possible to determine whether it is in the process of artificial insemination to damage genetic material, a disturbance in the number of chromosomes, etc. These procedures are used to mother spared spontaneous abortions, reduce the chances of multiple birth, as well as to select out an embryo that is in the best condition, which gives a greater chance of success interventions. In addition, it is possible to test for the presence of gene alleles inherited disorders, as well as a wide range of other information.
These methods are used to determine the different genetic abnormalities, and predisposition to a variety of serious diseases, and the number of genes associated with pathological conditions that can be examined is increasing. Same as with any new technology, here is also the main problem - the problem of borders. Like everything else, these technologies should be used within the limits of the moral.
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