One Boy Coming Right Up! Preimplantation Genetic Diagnosis and Sex Selection

1. Objectives

  • Review the basic current screening procedures available both pre- and post-conception
  • Understand the concept of Mendelian X-linked recessive diseases as well as late-onset genetic diseases
  • Discuss the difference between sex and gender
  • Explore the ethical questions raised by a real-life case in order to stimulate discussion in the classroom

Curriculum Integration Ideas

This brief may be used in life science classes during units for topics including:

  1. Human reproduction
  2. Basic concepts in human psychology regarding sex, gender, and orientation
  3. Public policy discussions on medical regulation and healthcare reform

2. Preimplantation Genetic Diagnosis

It is estimated that fifteen percent of couples in America are infertile, that is they are unable to achieve pregnancy after one year of regular, unprotected intercourse. Many of these couples turn to the rapidly advancing science of fertility medicine in the hope that assisted reproductive technologies will help them have children. Two of the newest technologies are those of preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS).

PGD/PGS are unique in that they are performed preconception, whereas many older screening tests are performed after conception has occurred and the fetus is developing in utero. PGD/PGS involve testing an oocyte (egg) or an embryo in the laboratory. PGD refers to when physicians and scientists look for specific genetic diseases, while PGS is a screening procedure where at-risk oocytes or embryos are identified.

Before PGD/PGS were developed, post-conception screening techniques were the only option available to identify fetuses with genetic diseases. These screening techniques are still the most commonly used method and involve amniocentesis (testing the amniotic fluid in the womb), ultrasound, blood tests, as well as biopsying a small part of the placenta.

3. A Closer Look - Potential Applications of PGD

PGD can be used for many genetic traits. Some of these traits are markers for disease, others are not. For example, people with Down syndrome have an extra 21st chromosome (most humans have 2 copies of 23 chromosomes in their genes). Individuals with Down syndrome have lower than average cognitive abilities; distinct facial and bodily features; and are at an increased risk for cancer, Alzheimer's, heart defects, and many other medical problems. PGD can identify embryos with this extra 21st chromosome so that couples can choose to implant another embryo and avoid having a child with Down syndrome, if they so choose.

Other diseases, however, are more difficult to pinpoint genetically or follow patterns of expression that are less predictable than Down syndrome. One group of these diseases is those that are X-linked recessive. Only a male whose mother carries the gene for one of these diseases will actually have an X-linked recessive disease. An example of an X-linked recessive disease is Duchenne muscular dystrophy, a severe disease that causes muscle fibers to degenerate. Here is a link on Mendelian genetics to refresh your knowledge of basic inheritance patterns.

Another type of disease that can be recognized through PGD is the family of those that are considered late-onset, and an example of one such disease is Huntington's disease. Huntington's affects nerve cells and leads to difficulties with walking, coordination, and cognition. Finally, PGD/PGS can also be used for sex selection - that is to differentiate between male and female embryos. It is important to remember the difference between sex and gender. Sex is a medical term referring to whether one has XX or XY chromosomes, while gender is a psychological one.

4. What Are Some Of The Ethical Issues Raised?

There are a wide variety of ethical issues that have been raised by the use of preimplantation genetic diagnosis. One of the thorniest is the use of PGD for sex selection. Some of these concerns are -

Gender Discrimination

In many cultures, and to a lesser extent here in America, male children are highly prized over female children. Males are valued not only since they carry on the family name and property, but also for economic security. If PGD is used by parents to select the gender of their child, there is worry that male embryos will be selected predominantly and a new form of gender discrimination will result. What message does this send to both males and females? What if a male child is selected against in the case of X-linked recessive disease in the family? For example, if a mother knows she carries the gene for Duchenne's, is it wrong if she chooses a female embryo over a male one? Is this also gender discrimination or is this a valid and ethical use of PGD?

Disability Rights

Disability rights proponents have devoted years to fighting for equality for those that are disabled. If PGD is used to select against those with genetic conditions, such as Huntington's, Down syndrome, or countless others, some have argued that this is a form of discrimination against those with disabilities. What do you think? Are we sending the message that those with disabilities are undesired by society?

Distributive Justice and Regulation of PGD

PGD is an expensive procedure that requires thousands of dollars. However, the cruel irony is that while the rich can afford infertility treatments, it is the poorest members of society that suffer with the highest rates of infertility. Is it fair, then, to allow only people that can afford expensive medical services ensure that their children are free of disease? Secondly, PGD, like much of infertility medicine, is largely unregulated by the government. Individual physicians are therefore free to use their own judgment regarding what is ethical and what is not. So, it may be possible that some physicians are willing to engage in using PGD for sex selection while others are not. Is this acceptable?

Review Questions

  1. Explain some of techniques available for both pre- and postconception counseling.
  2. Detail the difference between sex and gender.
  3. Identify three ethical issues that arise from the use of PGD for sex selection and discuss your opinions on each.
  4. In what ways has our society made improvements regarding gender and disability discrimination? Can you point to examples that show improvement is still necessary?

References (links offsite)

Repro Ethics