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What is Preimplantation diagnosis?In Making Astronauts, which is set in the not too distant future, Martin and Adam’s child is to be conceived by in vitro fertilization and genetic screening using preimplantation diagnosis. All these technologies are currently available and in use.
What is preimplantation diagnosis? Preimplantation diagnosis (PGD), is a diagnostic procedure, used in genetic screening, in which a single cell is removed from an embryo two or three days after it has been conceived through in vitro fertilization. In IVF, eggs are gathered from the woman's ovaries and mixed with the man's sperm in a dish in the laboratory. "In vitro" is a Latin term literally meaning "in glass". It refers to the glass container in the laboratory where fertilization takes place. Although this is usually a dish, in the popular mind it was thought to be a test tube - hence the term "test-tube baby". Thousands of IVF babies have been born worldwide since the technique was first used successfully in 1978. At two or three days of age the embryo consists of about eight genetically identical cells. The embryo itself is unaffected and continues to grow while the selected cell’s genes are replicated using polymerase chain reaction and then studied for genetic defects. The procedure allows an embryo to be tested before it is implanted into the womb when an inheritable disease is carried by or exhibited in one or both parents. Embryos that test positive are discarded, while embryos that test negative are considered for selective implantation. Typically, between one and six embryos are implanted, four days after fertilization. Prior to PGD, the only form of screening for genetic disorders was prenatal diagnosis. There are two sampling methods available to detect harmful genetic conditions in embryos and developing fetuses. Amniocentesis Currently the most widely used technique of prenatal diagnosis. It is commonly carried out between 15 and 18 weeks of pregnancy. Ultrasound is used to locate the placenta, and a small quantity of amniotic fluid, which contains cells shed by the developing fetus, is withdrawn through a needle from the amniotic cavity. Cells have to be cultured for two weeks before chromosome examination (for example, to detect Down’s syndrome) or DNA analysis can take place. Chorionic villus sampling Introduced more recently, chorionic villus sampling is a procedure whereby a small sample of chorionic (placental) tissue is removed for prenatal diagnosis. Chorionic villis originate from the developing embryo and are removed either by inserting a needle through the abdomen, or by a small 'biopsy forceps' passed through the vagina. Samples can be taken at any time after 10 weeks of pregnancy. Because the cells are derived from the embryo, they nearly always provide a reliable guide to the genetic make up of the fetus. Early results can be obtained within two days. When is PGD currently used? PGD is used for an increasing range of genetic defects, including those causing cystic fibrosis, beta thalassaemia, myotonic dystrophy, Huntington’s disease, Charcot-Marie-Tooth disease, Duchenne and Becker’s muscular dystrophy, haemophilia, fragile-X syndrome. In the past, couples wishing to ensure that a genetic disease did not affect their fetus had only the option of prenatal diagnosis by amniocentesis or chorionic villus sampling. The technology of PGD spares the couple the difficult decision of subsequent clinical abortion, because only embryos that do not have the potential to develop a genetic disease are transferred to the woman's uterus for implantation. What are the current ethical implications? The use of PGD, has often been referred to in the press and in popular debate as a question of ‘designer babies’. ‘Designer baby’ is one of those terms, like ‘Frankenstein foods’ and ‘slippery slope’, which is central to public discourse on genetics, but which can be misleading. The selection of embryos before implantation to ensure that a couple’s fetus is not affected by a genetic disorder, is an example of the selection or choice of an alternative option rather than the manipulation or design of babies. The possibility of truly designing a child, by choosing characteristics from a menu of possibilities, for example using gene therapy, is still in the realms of science fiction. The ethical implications of PGD are associated with several factors. First, new reproductive technology may encounter ethical and religious objections that are associated with protection of the beginning of life within the definition of "personhood" or "human being." There is no consensus regarding the point in the process of fertilization that marks the beginning of human life. For some it is the penetration of the sperm into the oocyte, whereas for others it is the fusion of the nuclei. Some may differentiate between the moral status of cells such as an oocyte, zygote, or embryo. With diagnostic procedures that are performed when an embryo exists, is deference to be shown to the embryo because of the sanctity of human life? In most scientific circles an embryo is considered to be rudimentary. Embryos are regularly discarded in other circumstances, such as unwanted frozen embryos from IVF and in the natural selection process of loss of fertilized eggs in menstrual cycles. A decision to discard unused embryos with a serious genetic defect recognized with PGD technology is ethically acceptable to most. However, other views include the issue of respect for the sanctity of human life prohibiting the discard of human embryos. If the "soul" of the individual starts as early as fertilization, then 60% to 70% of embryos or "souls" will never implant. Approximately 20% to 25% of implanted embryos will result in miscarriage. With these scientific data, the United Kingdom decided to permit research on human embryos for up to 14 days after fertilization. The ethical dilemma for some with PGD is whether the embryo is considered to have a "soul" or is just a potentially implantable set of cells that may result in a human being under the correct implantation circumstances. What would the ethical implications be if it where possible, as in the drama, to use preimplantation diagnosis in relation to the selection of embryos for/against behavioural characteristics such as sexuality, intelligence, criminality. While it is not currently possible to screen for genes associated with behavioral traits, with the significant advances in our knowledge of genetics and publication of the draft sequence of the human genome, the focus of research has moved once again towards understanding the biological contribution to behavior. Some researchers are attempting to locate specific genes, or groups of genes, associated with behavioral traits and to understand the complex relationship between genes and the environment. Just as in Making Astronauts, it may be possible, at some point in the future, for parents to screen for behavioral traits. What would the ethical implications be of the use of preimplantation diagnosis? “We do accept that, at present, the case for permitting prenatal selection based on the identification of genetic predispositions for enhanced abilities remains to be made. We recommend, therefore, that the technique of preimplantation genetic diagnosis, which is currently restricted to serious diseases and disorders, should not be extended to include behavioural traits in the normal range such as intelligence, sexual orientation and personality traits” Genetics and Human Behaviour: the ethical context. The Nuffield Council on Bioethics Whereas selective termination following pre natal diagnosis (PND) is applied to a fetus that has already implanted and is developing in the womb, PGD is used to select which embryos to implant. Thus, PGD does not precede the termination of a potential human life, but precedes, instead, the choice as to which embryo, among those created by IVF, is to be given a chance of developing into a human being. And in this context, it is not so clear that it is morally unacceptable to make this choice on the basis of genetic information about behavioural traits. Whereas PND would be used to end a life, PGD is, in effect, used to choose which life to start. Hence, the moral prohibitions which apply in the case of PND, do not apply in the same way in the use of PGD. Nonetheless, the potential use of PGD to select embryos that are more or less likely to exhibit particular behavioural traits is widely thought unacceptable. One line of argument in favour of the use of PGD is described in terms of a ‘right to procreative autonomy’ which would include a right to employ safe and reliable methods for the selection of children with a genetic predisposition for enhanced abilities within the normal range. But what about the question of Natural Humility? “At present, parents accept their children as they find them in an attitude of ‘natural humility’ to the unchosen results of procreation. This attitude is an important feature of parental love, the love that parents owe to their children as individuals in their own right; for this is a love that does not have to be earned and is not dependent on a child having characteristics that the parents hoped for. Parental love which includes this element of natural humility is, therefore, incompatible with the will to control. It is not compatible with attempts to interfere in the life of a child except where the interference is in the child’s own interest. Equally, it is not compatible with the practice of prenatal selection which seeks to identify, as a basis for choice, genetic predispositions for enhanced abilities or special character traits. For this is an attempt to determine the kind of child one will have – which is precisely not the unconditional, loving acceptance of whatever child one turns out to have’’. Genetics and Human Behaviour the ethical context.The Nuffield Council on Bioethics
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