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Preimplantation Genetic Diagnosis
- Preimplantation Genetic Diagnosis
- Science & Policy History
- Ethics
- The Arts
- Media Monitoring
- Comments
- References & Links
What is Preimplantation Genetic Diagnosis?
Preimplantation Genetic Diagnosis (PGD) involves the testing of embryos produced through in vitro fertilisation (IVF) for the presence of a range of genetic disorders. It may be considered as an early form of prenatal diagnosis. A single cell is removed from an embryo at the eight-cell stage of development (around three days old), leaving the rest of the embryo intact. The DNA from the removed cell may then be analysed to determine a range of genetic characteristics including the presence of sex chromosomes, extra genetic material (as in Down syndrome) or genetic variants such as the BCRA1 gene associated with familial forms of cancer1. In practice a large number of embryos are usually created by IVF and each embryo is then tested by PGD. A decision can then be made to select one or more unaffected embryos for reinsertion into the mother’s womb. This process is termed PGD with embryo selection.
Science & Policy History
Robert Edwards and David Gardner reported the successful sexing of rabbit blastocysts in 1967. (A blastocyst is the term for the embryo at a stage of approximately 70-100 cells). This procedure is generally seen as the first step towards PGD. Further development of PGD depended on the development of the highly sensitive technology of polymerase chain reaction (PCR). The PCR technique was conceived in 1985 by Kary Mullis, designed as an in vitro simplified reproduction of the in vivo process of DNA replication2.
Using PCR it is possible to obtain a large quantity of copies of a particular stretch of genome, upon which further analysis can be made. As a result, it is a highly sensitive and specific technology that lends itself to various forms of genetic diagnosis including PGD. Successful PGD testing first took place in October 1989 by Handyside et al, with the first births occurring in 19903. In these cases, PCR was used for sex determination for patients carrying X-linked diseases. In other words PGD was used to select female embryos for reimplantation, because of the presence of an X-linked disorder which only affected males. PGD can be considered as a form of prenatal genetic screening which can be performed prior to implantation. Once a cell has been obtained from each embryo, DNA is extracted and a range of diagnostic procedures can performed. In general, PCR based methods are often used to detect monogenic disorders (genetic conditions caused by an abnormality within a single gene) and fluorescence in situ hybridisation (FISH) for those cases involving major chromosomal abnormalities (such as Downs syndrome) or to obtain the sex of the embryo.
The FISH technique has been reported to have between a 5 and 10% error rate4. A significant diagnostic difficulty is that the FISH technique may detect genetic abnormalities which do not correlate with subsequent significant disease. This may be due to phenomenon of mosaicism where only some cells within the body are affected by chromosomal abnormalities, and other cells are unaffected. As a result, questions have been raised as to whether one cell extracted from an embryo can be taken to be representative of the complete embryo. In addition viable embryos may also be discarded if the diagnostic technique is unsuccessful. Currently PGD is being recommended for two main groups of patients:- Couples with a high risk of transmitting an inherited disease, for which a genetic test exists.
- Couples who undergo IVF treatment and whose embryos are screened for chromosome abnormalities (PGS) to increase the chances of an ongoing pregnancy.
The clear advantage of PGD is that is allows couples who are at high risk of passing on a serious genetic disease, to have a child that is their genetic offspring but who does not carry the disease. Essentially PGD allows the selection of a healthy embryo rather than the genetic manipulation or therapy of an affected embryo. At present in the UK, PGD is most commonly used in sexing embryos in order to avoid X-linked disorders and testing for chromosomal abnormalities, such as Down’s syndrome. Cystic fibrosis is the most common single gene disorder tested for using PGD. However as more genetic tests become available, the list of conditions which can be identified is steadily increasing, including Tay-Sachs disease, Duchenne muscular dystrophy, Lesch Nyhan syndrome and Marfan syndrome5.
In the UK, following public consultation, The Human Fertilisation and Embryology Authority (HFEA) agreed in May 2006 that it would consider the use of PGD embryo testing for late onset conditions such as inherited breast, ovarian and bowel cancers, in view of the aggressive nature of the cancers, the impact of treatment and the extreme anxiety that carriers of the gene can experience6. The HFEA decision only deals with serious genetic conditions that can only be tested for using a single gene test. An inherited tendency to most medical conditions, such as asthma and eczema, is the consequence of multiple genes, and cannot be currently identified by PGD. Click here for the full report from the HFEA.
Ethics
- An alternative to selective abortion
- An alternative to germline modification
PGD is technically ineffective when it comes to traits that depend on two or more genes. However for serious single-gene disorders, PGD is capable of preventing the births of children with serious genetic diseases, and may also allow the detection and prevention of the birth of children who are genetic carriers. PGD does not involve the modification of human genetic material as in germline gene therapy.
Disadvantages8
- Elimination over treatment
- A form of eugenics?
Further controversy surrounds PGD because of its eugenic implications. Disability rights organisations in particular have criticised PGD because of the lack of control in its application in many countries and the subjective definition of what is termed a “disease” which can be screened for and eliminated.
Dr Tom Shakespeare, a social scientist who has achondroplasia, has written extensively on the subject of genetics and disability. He is keen to see active engagement and participation from the disability community in discussions over PGD and prenatal screening. He opposes the introduction of blanket legislation on PGD and champions choice at the beginning and end of life.
Rachel Hurst, Director of Disability Awareness in Action, argues that we need to create a society of diversity that values, accepts and empowers those who have disabilities, as opposed to one that is intent on playing around with natural selection in order to establish a “perfect society”9. A notion of a perfect society may sound wonderful and enticing but how far could it go? Hurst argues that it is very difficult (if not impossible) to decide whose idea of perfection is the correct one. To decide on one model of human perfection is dangerous and damaging to society as a whole.
- Designer babies
Many people are concerned that PGD will ultimately be used to enhance parental choices in non-medical areas. For instance it may be used to select a child of a preferred sex and possibly to determine a child’s cosmetic, behavioural and other characteristics. It is becoming increasingly apparent that worldwide PGD is being used for sex selection for non-medical reasons.
A survey carried out in the USA found that 9 per cent of clinics were providing this service. Half of such clinics were performing such procedures on the basis of “family balancing”, where a couple with two or more children of one sex desire a child of the other sex. However, half of the PGD clinics approached did not restrict sex selection to family balancing. In the UK, sex selection for “family balancing” is currently illegal and the HFEA consultation document on PGD reaffirmed this position. It recommended that PGD should not be used for frivolous or ‘social’ reasons10. The document went on to recommend that the use of PGD should be consistent with the use of post-implantation prenatal diagnosis (PND) or conventional foetal screening.
- Success rates and the subsequent costs
In the UK, PGD was first introduced in 1990 and yet by 2000 there were only 30 PGD cycles a year being undertaken in the UK. This is in direct contrast to 30,000 IVF cycles11. This discrepancy reflects the fact that current PGD technology is not widely available and has a low success rate. IVF success rates (that is the percentage of cycles which result in a live birth) currently averages 17% per cycle12, and PGD rates are probably similar or lower than IVF as a whole.
Moreover, the costs involved with PGD are considerable, and in most countries the entire expense is met by the patients themselves. With continuing technical advances it is likely that PGD will become more widely available and more successful in the future. As procedures develop, those who are able to afford may increasingly take the opportunity of using PGD. Hence as with most reproductive technology there are major concerns about social divisions between the affluent and the poor. It is conceivable that, in time, rich sections of society will improve their genetic inheritance compared with the poor as they are able to pay to gain “better genes” for their children.
- Doubt over accuracy of diagnosis
The Arts
Visual Arts
Creative Time DNAid ™ by Creative Time
Creative Time is a New York based public art organization. As a way to address concerns about genetic technology and its possible impact on society, DNAid was created to provoke public conversation on the topic. To do so, it commissioned five artists to create deli coffee cups. Gene patenting is dealt with in Larry Miller·s cup when he asks, "Who Owns Your Genes?&rdquo. The artist included two fingerprint markings on the cup to show that a person·s DNA could be left behind on their cup. This piece can be viewed at:
Media Monitoring
Business is booming in sex selection
It's one thing to wish for a baby boy or girl, quite another to make it happen. Amanda Mitchison meets the couples heading abroad – where the sex selection business is booming.'Gender-based' abortion legal in Sweden
Swedish health authorities have ruled that gender-based abortion is not illegal according to current law and can not therefore be stopped, according to a report by Sveriges Television.Assisting Reproduction, Testing Genes: Global Encounters with New Biotechnologies
By looking at the impact and applications of these technologies through this lens, a fascinating set of perspectives and insights can be garnered in terms of understanding the adoption of new developments in science and technology within different cultural contexts. Within the context of global-local, the book helps to identify the challenges which arise from local understanding of advances in science and technology. This is what Assisting Reproduction, Testing Genes: Global Encounters with New Biotechnologies seeks to do with specific reference to ART and does so rather well.Build your own baby
Unable to have a baby of her own, Amy Kehoe became her own general contractor to manufacture one. For Ms. Kehoe and her husband, Scott, the idea seemed like their best hope after years of infertility.Demand for designer babies will grow
Parental demand for “designer babies” screened to lack faulty genes will grow dramatically over the next decade, with new discoveries about the influence of DNA on health, a leading geneticist has predicted. As science learns more about the genetic roots of disease, couples will increasingly seek DNA tests on their embryos when starting a family, according to David Goldstein, of Duke University in North Carolina.
My Sister's Keeper
Reviewed by Kyle Scott
Although, this book has been around for some time it seems appropriate to review it now since in the debate surrounding the Human Fertilisation and Embryology Bill MPs have voted to permit the creation of Saviour Siblings. If this is a book that you haven’t had a chance to look at yet, then I strongly recommend it as an addition to your summer reading list.
Paying for a sibling to save Mark
Treating a child with a genetic disorder is costly for the NHS and heartbreaking for families.Saviour sibling success in the UK
The BBC's Fergus Walsh reports on a nine year old girl from Norfolk who has had a life-saving transplant from a so-called saviour sibling; the first time the treatment has been successfully completed in the UK.Sex selection in Vietnam produces boy boom
Vietname is seeing a boom in male births as increasing numbers of parents opt for sex-specific abortions.The arrival of the prenatal home testing kit
A new at-home test that can determine the gender of a fetus at 10 weeks with 80 per cent accuracy might sound exciting to some but it worries others.The neurological consequences of PGD
Preimplantation genetic diagnosis (PGD) has helped many couples conceive healthy children and is generally considered a safe practice. However, a new long-term analysis of PGD in mice suggests that this procedure may increase risks of weight gain and memory decline in adulthood.Two couples suing doctors for failing to diagnose Down Syndrome
Two New Zealand couples are suing doctors for failing to diagnose Down Syndrome in their unborn babies, denying them the chance to terminate the pregnancies.US clinic offer designer babies
A US clinic has sparked controversy by offering would-be parents the chance to select traits like the eye and hair colour of their offspring.Yury Verlinsky, Expert in Embryonic Screening, is dead at 65
Yury Verlinsky, who was one of the first scientists to develop techniques to detect genetic disorders in embryos and who helped make that screening available to parents around the world, died July 16 in Chicago. He was 65.
Comments
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References & Links
- Center for Genetics & Society (2003), Preimplantation Genetic Diagnosis (PGD) and Screening, http://www.genetics-and-society.org/technologies/other/pgd.html [accessed 23rd January 2007].
- Ibid.
- Ibid.
- Ibid.
- Song, R. (2002), Human Genetics: Fabricating the Future, (Darnton, Longman, Todd: London), p.22
- Human Fertilisation & Embryology Authority, Authority Decision on PGD Policy, 10th May 2006, http://www.hfea.gov.uk/cps/rde/xchg/SID-3F57D79B-A11CE70E/hfea/hs.xsl/1124.html [accessed 23rd January 2007].
- Center for Genetics & Society (2003), Other Human Genetic & Reproductive technologies: Arguments, Pros and Cons, http://www.genetics-and-society.org/technologies/other/arguments.html#2 [accessed 23rd January 2007].
- Ibid.
- Hurst, R. (2006) “The Perfect Crime” in ¬Better Humans? The politics of human enhancement and life extension, (Demos Collection 21: London)
- Human Fertilisation and Embryology Authority, November 2001, Outcome of the Public Consultation on Preimplantation Genetic Diagnosis, http://www.hfea.gov.uk/cps/rde/xchg/SID-3F57D79B-CE55042B/hfea/hs.xsl/380.html#PGD [accessed 18th January 2007]
- Song, p.22
- Ibid.