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Pre-implantation genetic diagnosis (PGD) & haplotyping (PGH)
Current status; Objections; Advantages
Sponsored link.
Current status of the PGD procedure:
Initial PGD research was performed in the UK during the late 1980s. It
remains a rare procedure that is only available in a few clinics worldwide. It
can be used to detect a few hundred disorders and diseases. There is the potential that it
will detect many hundreds eventually. 1
According to the Sher Institute:
"By the year 2000, more than 1500 couples
had participated in PGD clinical trials, which are ongoing in several centers
around the world, and more than 1000 PGD/IVF cycles had been performed, In
virtually all of these cases, PGD was followed by early prenatal genetic
diagnosis to eliminate the risk of misdiagnosis through PGD. Several such errors
in PGD have been recorded to date. These pregnancies were all terminated,
electively." 2
According to Anuja Dokras of the Yale University School of Medicine:
"This technique is currently available to couples whose
offspring are at a high risk (25-50%) for a specific genetic condition
due to one or both parents being carriers or affected by the disease.
Also the genetic code associated with the condition must be known in
order to allow diagnosis. Currently it is not feasible to routinely
screen women at lower risks, such as women over age 35 for Downs
Syndrome..." 3
An article in The Guardian, a UK newspaper quotes The Human
Fertilisation and Embryology Authority, (HFEA) as describing PGD as "a
physically and mentally demanding process which does not bring any
guarantee of success." With PGD, the live birth rate is probably even
lower than the average 17% IVF success rate, and the whole procedure is
considerably more expensive. 4
Objections to the PGD procedure:
 | Conservative Christians and others typically people believe that
human personhood begins at conception. This means that any destruction
of an embryo is equivalent to the murder of a human person. There are a number
of concerns that they have about PGD:
 | The cell that is removed could conceivably, under the right
conditions, develop into a fetus on
its own. But the testing will destroy it. |
| The fertilized cells that are not implanted are usually destroyed,
as in in-vitro fertilization procedures. |
| If a genetically defective cell is found, then the entire embryo
from which it was extracted is destroyed. |
|
| Dr. Patricia Baird, a geneticist who led the Canadian Royal Commission on New
Reproductive Technologies said: "Because there is so much money involved,
there is a real danger of premature, unwise application of this procedure." We
find this comment confusing. The procedure would cost in the vicinity of $4,500 to $7,000
in US funds. One might argue that because of the high expense involved, the
procedure would only be applied in unusual cases after much careful thought. |
| A genetically defective fertilized egg, if allowed to mature and cause a live birth, it
would not necessarily generate a disorder or disease in the individual. Various genetic
variations (called alleles) have a penetrance factor, which is a measure of their
effectiveness or power. For example, the allele which causes Huntington's Disease has a
100% penetrance: if you have the allele, you will certainly develop the disease. But other
genetically determined conditions have a much lower penetrance: left handedness is only
about 15%; the gene(s) that cause homosexuality
have a penetrance factor that is about 67% -- between that for
Huntington's and left-handedness. Thus, many embryos would be killed which would never have caused a disease or
disorder. |
| Some genetically caused diseases only develop symptoms when the person is in their 30's
or 40's. By that time, a cure might have been found. |
| The procedure could be the start of a slippery slope. Perhaps embryos would be
eliminated that might leave the individual at higher risk for heart disease, or stroke, or
obesity, etc. And there is the possibility that the procedure could be used to eliminate
female embryos, or embryos that would grow into adulthood with a minority sexual
orientation -- bisexuality or homosexuality. This is an ironic situation:
religious conservatives, who are most likely to have a strong preference
for a baby that would mature as a heterosexual adult, would be exactly
the group who are most opposed to PGD which has the potential to
eliminate homosexuals at the embryo stage. |
| Some religious and social conservatives are worried that the
technology could lead to the creation of babies to be used for spare
parts. |
| CitizenLink, a service of Focus on the Family Action -- a
fundamentalist Christian group -- published a brief article objecting to
abortions triggered by the discovery of Gaucher disease in an embryo or
fetus. They describe it as "a treatable genetic disorder." Their
concern would also apply to cases where the disease is detected using PGD.
They believe that parents are sometimes not given a full understanding of
the disease. Focus/Action wrote: |
"Dawn Vargo, associate bioethics analyst at Focus on the Family
Action, said it's just the latest example of the ethical problems
that can be associated with prenatal screening. 'This study provides
evidence that parents who receive screening on complex genetic diseases
may choose to abort their children based on misinformation or lack of
information'." 7
According to Wikipedia, Gaucher's disease:
"... is the most common of the lysosomal storage diseases. ...
Symptoms may include enlarged spleen and liver, liver malfunction,
skeletal disorders and bone lesions that may cause pain, severe
neurologic complications, swelling of lymph nodes and (occasionally)
adjacent joints, distended abdomen, a brownish tint to the skin, anemia,
low blood platelets and yellow fatty deposits on the sclera. Persons
affected most seriously may also be more susceptible to infection. ...
The currently existing treatment of Gaucher's disease, Cerezyme
(imiglucerase for injection), costs up to $550,000 annually for a single patient and
the treatment should be continued for life." 8
Various forms of the disease occur in about 1 in 25,000 live births. Some
versions of the disease can cause serious convulsions, mental retardation,
dementia, etc.
Focus did not mention what "misinformation or lack of information"
parents were provided with.
Sponsored link:
Advantages to the PGD procedure
| Most genetic testing now is done through amniocentesis when the fetus is 12 to 16 weeks
old. The results are typically available after a wait of an additional three
weeks. In this, a sample of the amniotic fluid is drawn from around the fetus.
A floating cell from the fetus is then found and analyzed. If the
analysis shows that the fetus is genetically defective, then the parents
have the option of aborting the fetus. Essentially all couples in North
America and the UK do elect
to have an abortion. Amniocentesis is be far more distressing than
Pre-Implantation Genetic Diagnosis to most couples,
because it is performed at a time in gestation when the fetus is so fully developed. The PGD technique is
performed before pregnancy begins; it would avoid much of the stress and
moral conflict in most couples. However, strongly pro-life couples may
not differentiate morally between the destruction of a three-month fetus
and an eight-cell embryo; they may consider both to be fully human
persons. |
| Some adults who know that they are carriers of a genetically transmitted disease decide
use contraception in order to not have children. The Pre-Implantation Genetic Diagnosis procedure allows
them to have a child with full assurance that it would not be carrying that disease. (Of
course, the child could be born with other malformations, diseases and disorders that were
not tested for.) |
| If the procedure became widespread, the incidence of many diseases would be reduced,
since few people with the disease would be born and later have children. |
| The procedure could significantly reduce the cost of medical systems in North America.
Treatment of some genetic diseases can easily cost millions of dollars over the
lifetime of a single individual. |
References:
The following information sources were used to prepare and update the above
essay. The hyperlinks are not necessarily still active today.
- "Fact sheet: Preimplantation Genetic Diagnosis, American Society
for Reproductive Medicine, at:
http://www.asrm.org/ This a PDF document.
You can obtain a free software to read this type of file from Adobe.
- "Pre-implantation genetic diagnosis (PGD) A commentary on its utility
and potential value," at:
http://www.sirm.com/
- Anuja Dokras, M.D.Ph.D., "Pre-Implantation Genetic Diagnosis",
Pre-Implantation Genetic Diagnosis, Vol.1 No.5. See: http://www.hygeia.org/
- Sarah Boseley, "Public views on embryo genetic testing sought,"
http://www.guardian.co.uk/
- "Screening for Treatable Genetic Disorder May Lead to More Abortions,"
CitizenLink, 2007-SEP-19, at:
http://www.citizenlink.org/
- "Gaucher's disease," Wikipedia, 2007-SEP-03, at:
http://en.wikipedia.org/
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Copyright © 1999 to 2007 by Ontario
Consultants on Religious Tolerance
Latest update: 2007-SEP-20
Author: B.A. Robinson
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