Pgd designer babies



Electroporation is a technique in which high voltage pulses are used to carry DNA into the target cell across the membrane. The method is believed to function due to the formation of pores across the membrane, but although these are temporary, electroporation results in a high rate of cell death which has limited its use. [35]. An improved version of this technology, electron-avalanche transfection, has since been developed, which involves shorter (microsecond) high voltage pulses which result in more effective DNA integration and less cellular damage. [36]. PGD regulation is determined by individual countries' governments, with some prohibiting its use entirely, including in Austria, China, and Ireland. [12]. Another screening technique, fluorescent in situ hybridisation (FISH) uses fluorescent probes which specifically bind to highly complementary sequences on chromosomes, which can then be identified using fluorescence microscopy. [11]. Viral vectors work efficiently and are mostly safe but present with some complications, contributing to the stringency of regulation on gene therapy. Despite partial inactivation of viral vectors in gene therapy research, they can still be immunogenic and elicit an immune response. This can impede viral delivery of the gene of interest, as well as cause complications for the patient themselves when used clinically, especially in those already suffering from a serious genetic illness. [32]. Embryos for PGD are obtained from IVF procedures in which the oocyte is artificially fertilised by sperm. Oocytes from the woman are hAvrested following controlled ovarian hyperstimulation (COH), which involves fertility treatments to induce production of multiple oocytes. After hAvresting the oocytes, they are fertilised. Another difficulty is the possibility that some viruses will randomly integrate their nucleic acids into the genome, which can interrupt gene function and generate new mutations. [33]. Whilst germline engineering has mostly been performed in mammals and other animals, research on human cells in vitro is becoming more common. Most commonly used in human cells are germline gene therapy and the engineered nuclease system CRISPR/Cas9. One application of PGD is the selection of ' saviour siblings ', TEENren who are born to provide a transplant (of an organ or group of cells) to a sibling with a usually life-threatening disease. Saviour siblings are conceived through IVF and then screened using PGD to analyse genetic similarity to the TEEN needing a transplant, in order to reduce the risk of rejection. [8]. Selection based on sex is permitted under certain circumstances, and genetic disorders for which PGD is permitted are detailed by the countries' respective agencies. When the gRNA binds to the target sequence, Cas will cleave the locus, causing a double-strand break (DSB). germline gene transfer clinical trials, in vitro trials are permitted. [27]. The CRISPR/Cas9 system ( CRISPR– Clustered Regularly Interspaced Short Palindromic Repeats, Cas9– CRISPR-associated protein 9) is a genome editing technology based on the bacterial antiviral CRISPR/Cas system. The bacterial system has evolved to recognise viral nucleic acid sequences and cut these sequences upon recognition, damaging infecting viruses. The gene editing technology uses a simplified version of this process, manipulating the components of the bacterial system to allow location-specific gene editing. [39]. Upon system delivery to a cell, Cas9 and the gRNA bind, forming a ribonucleoprotein complex. This causes a conformational change in Cas9, allowing it to cleave DNA if the gRNA spacer sequence binds with sufficient homology to a particular sequence in the host genome. [40]. The device generates a force to penetrate the cell membrane, allowing the DNA to enter whilst retaining the metal particle. In contrast, the United States federal law does not regulate PGD, with no dedicated agencies specifying regulatory framework by which healthcare professionals must abide. [13]. Process of pre-implantation genetic diagnosis. In vitro fertilisation involves either incubation of sperm and oocyte together, or injection of sperm directly into the oocyte. PCR - polymerase chain reaction, FISH - fluorescent in situ hybridisation. Polymerase chain reaction (PCR) is a process in which DNA sequences are amplified to produce many more copies of the same segment, allowing screening of large samples and identification of specific genes. [10]. Editing embryos in this manner means that the genetic changes can be carried down to future generations, and since the technology concerns editing the genes of an unborn baby, it is considered controversial and is subject to ethical debate. [4]. Once embryos reach the desired stage of development, cells are biopsied and genetically screened. The screening procedure varies based on the nature of the disorder being investigated. Genetically altered embryos can be achieved by introducing the desired genetic material into the embryo itself, or into the sperm and/or egg cells of the parents - either by delivering the desired genes directly into the cell or using gene editing technology. This process is known as germline engineering and performing this on embryos which will be brought to term is not typically permitted by law. [3]. Genetic engineering relies on a knowledge of human genetic information, made possible by research such as the Human Genome Project, which identified the position and function of all the genes in the human genome. [20]. Most commonly it is carried out using a vector, which transports the nucleic acid (usually DNA encoding a therapeutic gene) into the target cell. A vector can transduce a desired copy of a gene into a specific location to be expressed as required. Alternatively, a transgene can be inserted to deliberately disrupt an unwanted or mutated gene, preventing transcription and translation of the faulty gene products to avoid a disease phenotype.


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