Pre-implementation genetic diagnosis

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Pre-implantation Diagnosis (PDF, 2.07MB)

New developments in technology not only raise new problems for consideration, they also raise new questions about old problems such as questions concerning the definition of life itself--its commencement and termination.

Sometimes the terms PID (Pre-implantation Diagnosis) and PGD are used almost interchangeably in Anglo-American states. Both are forms of pre-natal diagnosis.

Pre-natal diagnosis means testing for diseases or conditions in a foetus or embryo before it is born. Pre-implementation genetic diagnosis (PGD) involves genetically testing an embryo (or occasionally an ovum) in a laboratory.

To achieve this, couples need to have in vitro fertilisation (IVF) treatment followed by a genetic testing stage. The aim is to make it more likely that a baby will be born free from a particular condition (usually a disease). This is a means of avoiding pregnancy termination or the destruction of an embryo.

The embryo is grown in the laboratory for a couple of days until the cells have divided and the embryo consists of eight cells. At this time one or two of the cells are removed. If the genetic code associated with the condition is know, these cells can then be tested to see if they contain the faulty gene that causes a particular condition.

One or two of the embryos without a copy of the faulty gene can then be placed into the woman for continuation of its development. Any remaining unaffected embryos can be stored for later use as required. For some, this raises ethical concerns related to when human life begins, the sanctity of human life and the issue of selective abortion.

The value of PGD is that the probability of having a child affected by the harmful genetic condition is diminished, with no need for a pregnancy to be terminated.

Medical uses

Two main groups of patients currently use PGD:

1  Couples with a high risk of transmitting an inherited condition.

This may be due to a single defective gene or a chromosomal structural abnormality. In these situations the purpose of PGD is to identify embryos carrying such a defect and destroy them.

2  IVF couples whose embryos are screened for specific conditions.

There are a number of possible future medical uses. Possibilities include the diagnosis of late-onset diseases such as Alzheimer’s disease or predisposition to diseases such as obesity, diabetes, heart disease, asthma, cancer and even disabilities such as deafness.

Non-medical uses

PGD has the potential to screen for genetic issues unrelated to medical necessity.

Increasingly, PGD is being used for sex-selection. A 2006 survey found that 9% of US clinics provided this service. Half perform it only for ‘family balancing’.

There are concerns that PGD could be used as a form of eugenics (the development of particular selected races or populations), which can be defined as ‘the science of improving the population by the control of inherited qualities’. This places a negative value on people with certain conditions or qualities when it is seen as ‘socially desirable’ to prevent further development of certain foetuses.

Financial considerations

The financial implications of medical interventions are often controversial. Some argue, for instance, that PGD could significantly reduce health care costs. Treatment of some genetic diseases can cost millions over the lifetime of a single individual. Some suggest that if births of these individuals could be avoided, then savings would be made.

For example, the lifetime treatment costs for someone with beta thalassemia in Britain are estimated at close to 200,000 pounds. This is likely to be considerably higher than the cost of tissue typing using PGD to select an appropriate ovum for development and subsequent stem cell transplantation from the resulting infant, although a precise costing is not available.

Ethical issues

Issues for parents

• There is a need to create and then select embryos on chromosomal or genetic grounds, with the deselected embryos then usually being discarded. This raises issues around the human dignity of the embryo.
• Invasive tests carry a significant risk of miscarriage and foetal death.
• It is not known whether the biopsy of one or two cells correlates with the ability of the embryo to further develop, implant and grow into a full term pregnancy.
• Tests may not provide a precise answer to medical questions.
• Ante-natal testing encourages women to view their babies as commodities that may be rejected if found sub-standard.

Issues for offspring

A principle of the Human Fertilisation and Embryology Act is that the best interests of the child produced by assisted reproduction must be paramount. So, what is in the best interests of the child?

• What if a stem cell transplant from an infant developed following PGD is unsuccessful? Would parents unconsciously blame the donor child? What will life be like for the child conceived to produce stem cells?
• Although a child may be born free of a disease, they may be likely to lose the parent from whom the disease-causing gene might otherwise have been inherited.
• There may be unexpected physical side effects and life-long consequences related to the genetic choice that are not appreciated at the time.
• The identification of a genetic mutation may mean that an individual is discriminated against and not able to obtain a job or insurance, obtain a mortgage or find a marriage partner.

Issues for society

Is it harmful to society if families choose their children on the basis of their genetic makeup?

• Opposition to the practice of seeking ‘designer babies’ raises concerns about eugenics at a societal level. To avoid this it is important that couples and not the state, professionals or other organisations retain control over reproduction and the decision of which children to have.
• Increased ante-natal screening may lead to loss of respect for, and victimisation of, the disabled and their parents.
• ‘Tidying away’ some hereditable diseases will not make society tidy, nor will it eliminate suffering.
• Some would argue that any attention to the gender of offspring is inherently sexist, particularly when social attitudes and expectations are involved.
• Many disabled people oppose screening because it is very difficult to support a practice that would have prevented one’s own existence. Increasingly, disabled people are perceiving these processes as a form of social discrimination against them.

Other ethical issues to consider

Relying on the result of testing only one cell from a multi-cell embryo assumes that this cell is representative of the remainder of the embryo. This may not be the case. PGD may result in a false negative result leading to the acceptance of an abnormal embryo, or in a false positive result, leading to the rejection of a normal embryo.

Some people object to the discarding of unused embryos. They generally feel that human personhood starts at the instant of fertilisation.

Other objections concern the fact of selection itself, which may remove some positive traits that are unrecognised.

‘Savior siblings?’

The Law Lords backed a 2003 Court of Appeal ruling that some couples undergoing fertility treatment could have their embryos screened to find tissue matches for seriously ill children. Advocates say the procedure will help save desperately ill children. Opponents fear it could lead to the creation of babies for spare parts.

Children have already been conceived to provide stem cells for their siblings use. PGD is used to select an embryo with the right genetic make-up to serve as a stem cell donor even in the absence of any family history of genetic disease.

The following could be asked: Who is harmed by allowing PGD to be performed solely for the benefit of a relative? Not the couple who wish to produce an embryo. Nor the child who would not otherwise have existed. Nor the person who receives the stem cell transplant that might save his or her life. It is argued that we must avoid the trap of interfering with individual liberty by preventing such procedures for no good reason, simply out of the ‘genophobia’ that grips much of society today.

A medical view

Genetic manipulation that is intended to be restorative, recreating a damaged length of DNA or replacing an abnormal gene variant with a normal counterpart, seems consistent with normal medical practice, but enhancing gene therapy can also attempt to improve on the original design.

In general, doctors have agreed that if no treatment is available then it is unethical to perform screening tests on apparently healthy people.