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Pre-implantation genetic diagnosis (PGD) & haplotyping (PGH)

Introduction; Sex-linked genetic
diseases; Clinics performing PGD


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Introduction:

PGD and PGH are procedures that can weed out genetically defective human embryos before they have a chance initiate a pregnancy. This is usually requested by prospective parents who are concerned about passing an incurable genetically based disease or disorder to their child. Typically one or both partners have been genetically screened previously, and found to be a carrier.

This "technically demanding and complex procedure" was developed only recently. 1 Currently, it is only available in a few clinics worldwide. It involves the following steps:

  • The woman is given drugs to produce "super-ovulation." She normally produces many eggs, which are collected.
  • As for a standard in-vitro fertilization (IVF) procedure, the eggs are placed in a dish and are fertilized by donated sperm (usually from the woman's partner).
  • About three days after IVF, each successful embryo has divided to about the 8 cell level.
  • This photograph shows the start of the procedure. Here, a 7-cell embryo which is fixed in position with a holding pipette at the left. A second pipette, on the right is used to drill a hole through the shell of the embryo. A single cell is dislodged from the embryo with a gentle suction. * The procedure is typically performed on an embryo at the 4 to 10 cells stage of development.
  • One or two cells are removed and is:

"... subjected to a molecular analysis. This requires the removal of the genetic material— DNA. This minuscule amount of DNA is amplified, meaning multiple copies are made through a molecular process known as PCR (polymerase chain reaction). These copies are then subjected to a molecular analysis that assists in identifying the sequence (code) that will determine the inheritance of the gene in question." 2

If a genetic defect is found, then the embryo from which it was taken is destroyed.

  • Typically, three of the embryos which are free of abnormalities are implanted in the woman's womb. The remaining, spare, preembryos are destroyed.
  • Sometimes, none of the embryos develop into fetuses, and the procedure is repeated. Often one lives and develop into a fetus which is later born. Less commonly, multiple births can result.

As of 2005, cells can be checked for dozens of genetically determined diseases. One site lists:

  • achondroplasia
  • adenosine deaminase deficiency
  • alpha-1-antitrypsin deficiency
  • Alzheimer disease (AAP gene)
  • beta thalassemia
  • cystic fibrosis
  • epidermolysis bullosa
  • Fanconi anemia
  • Gaucher disease
  • hemophilia A and B
  • Huntington disease
  • muscular dystrophy (Duchenne and Becker)
  • myotonic dystrophy
  • neurofibromatosis type I
  • OTC deficiency
  • p 53 cancers
  • phenylketonuria
  • retinoblastoma
  • retinitis pigmentosa
  • sickle cell disease
  • spinal muscular atrophy
  • Tay Sachs disease 3

Elsewhere on the Internet, websites also list: Fragile X syndrome,  Lesch-Nyhan syndrome - Retinitis pigmentosa, Charcot-Marie-Tooth disease, Barth's syndrome, Turner syndrome, Down's syndrome and Rett's syndrome. Female ova can be also be checked for a gene that increases the propensity to develop breast cancer. By mid-2006, about 200 diseases and disorders could be tested for. 4

The first "PGD baby" was born in 1989. 5,6  By 1997, over 30 babies had been born world-wide, following the use of this technique.

Dr. Perry Phillips, an obstetrician and gynecologist, is one of the directors of IVF Canada. He said:

"This is the beginning of the end of genetic disease…That's the dream of medicine. It's our dream. This should have the same impact [that] antibiotics did to bacterial disease."


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Sex-linked genetic diseases:

Many genetic diseases are sex-linked. For example, some are known to only be passed only on to male children; they are known as x-linked diseases. Thus, even if a particular sex-linked disease cannot be detected directly, the PGD method could theoretically be used to eliminate all of the male embryos and implant only female embryos. This would prevent the transmission of the disease to the next generation. Of course, just because such a technique is theoretically possible, it may or many not be considered an ethical procedure.

The University College Hospital (UCH) in London, UK, has applied to the Human Fertilisation and Embryology Authority for permission to use PGD techniques to help couples with a family history of autism. Boys are considerably more likely to develop autism than girls. The couple would go through the usual IVF procedure in which perhaps two dozen embryos are removed from the woman, all are fertilized and four of the healthiest embryos are implanted. They would deviate from the standard IVF procedure by culling out the approximately twelve male embryos from being considered for implantation. Professor Joy Delhanty of UCH said: "Normally we would not consider this unless there were at least two boys affected in the immediate family."

Josephine Quintavalle, of Comment on Reproductive Ethics, disapproves of this technique. She said:

"It is not about taking an embryo and curing it, but about diagnosing and then throwing away....The requirements are getting wider and wider and the science can be more and more hypothetical. This getting rid of male embryos is shoddy and shocking. We need to see more evidence on the genetic causes of autism." 7

Simone Aspis, of the British Council of Disabled People, warned:

"Screening out autism would breed a fear that anyone who is different in any way will not be accepted. It would create a society where only perfection is valued." 7


Some clinics that provide PGD:

We have found a few clinics that provide PGD and which have web sites on the Internet. None have asked to be included on this list; none have paid to be on the list:


References:

The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.

  1. "Using PGD to prevent sex-linked diseases," at: http://www.healthlibrary.com/ This web site has a remarkable series of microphotographs, including the one shown on this page. They show how a single cell is extracted from a seven-cell embryo. See: http://www.healthlibrary.com/
  2. Luba Djurdninocic, "Pre-Implantation Testing," at: http://www.vhl.org/
  3. Ricki Lewis, "Preimplantation Genetic Diagnosis: The next big thing?," The Scientist, 14[22]:16, 2000-NOV-13. See: http://www.the-scientist.com/yr2000/
  4. Ian Sample, "New embryo test to screen for 6,000 diseases," The Guardian, 2006-JUN-19, at: http://www.guardian.co.uk/
  5. Anuja Dokras, M.D.Ph.D., "Pre-Implantation Genetic Diagnosis", Pre-Implantation Genetic Diagnosis, Vol.1 No.5. See: http://www.hygeia.org/
  6. Fact Sheet: "Preimplantation Genetic Diagnosis", American Society for Reproductive Medicine, 1996-DEC. See: http://www.hygeia.org/
  7. Julie Wheldon, "Ethical row erupts over designer babies breakthrough," Daily Mail, 2006-JUN-19, at:  http://www.dailymail.co.uk/
  8. "Consultation document on preimplantation genetic diagnosis," The Human Fertilisation and Embryology Authority, at: http://www.hfea.gov.uk/

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 Home page > "Hot" topics > Abortion > Genetic topics > PGD/PGH > here


Copyright © 1999 to 2007 by Ontario Consultants on Religious Tolerance
Microphotograph shown by the kind permission of Dr. Malpani, of the Malpani Infertility Clinic, Bombay, India.
Latest update: 2007-SEP-20
Author: B.A. Robinson

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