Planting the Seed: How Preimplantation Genetic Diagnosis Will Change Our Children
Most Americans today are not intimately familiar with the field of reproductive genetics. Some obviously work very closely with the field, but others presumably accept that two people really only have one option when it comes to bearing a child. However, this lingering perception will most likely evaporate over the next several generations. For thousands of years, humans have gone about having children in the same way. The details of this well-known process matter not, but the shift away from this “traditional” method matter tremendously. Every day, scientists continue to work toward improving a technology known as Preimplantation Genetic Diagnosis, or PGD. Using the process of in-vitro fertilization and subsequent genetic analysis, PGD has the potential to significantly reduce, if not eliminate several genetic disorders. Diseases from hemophilia to Huntingdon’s chorea could disappear in a few generations, but unfortunately PGD also has the potential for misuse. If used considerately, though, PGD will revolutionize the way humans go about having children.
PGD distinguishes itself from other genetic diagnosis procedures through its use of in-vitro fertilization to create an embryo. First developed and used in 1978, in-vitro fertilization originally served only to help infertile couples conceive children. But since 1978, it has appeared in other realms of science, and its prevalence continues to rise (Reilly 238; Macer 23). This rise has ultimately led to an increased awareness of PGD, as couples employing the in-vitro process for any reason may choose to use PGD to increase the likelihood of conception (Van Voorhis 384). During the in-vitro process, the mother and father both provide gamete samples that can then form the zygote (fertilized egg), which soon becomes a blastocyst (small cluster of approximately eight cells). This entire procedure occurs in a laboratory setting, which thus gives the medical staff incredible control over the embryo’s development. This control matters tremendously as the zygote — or embryo after the first few weeks — will undergo genetic analysis before implanting in the mother’s uterus, hence the pre-implantation component of PGD.
Within the realm of modern reproductive technology, PGD distinguishes itself mainly from PreNatal Diagnosis, or PND. While both genetic analysis procedures carry a high cost, PGD generally costs less. And while the in-vitro process alone costs families thousands of dollars, it continues to become less expensive with technological advances (Van Voorhis 382). Nevertheless, PGD and the in-vitro process remain much safer and more economical than PND. With regard to the products of each, both procedures deliver a genetic analysis of an embryo’s genome before birth. However, PND does not employ the in-vitro process. Because of this, the analysis must occur while the child develops in utero, which then often results in the termination of the pregnancy, especially if the child shows specific genes, such as trisomy-21 (Down’s Syndrome). Given the enormous trauma associated with aborted pregnancies, PGD provides a clear advantage over PND by performing the genetic analysis pre-utero and almost eliminating the risk of terminated pregnancies (Verlinsky, et al 293).
As scientists continue to unravel the mystery of the human genome and its entire contents, more and more diseases and phenotypes will become predictable through the use of PGD. Currently, PGD can readily analyze and diagnose sex-linked diseases, which result from genes (or the lack thereof) on the 23rd pair of chromosomes in humans, also known as the sex chromosomes. This analysis can occur without even examining the actual genome of the zygote, simply by seeing what chromosomes exist in the embryo. In humans, who have an X-Y sex-determination system, this pair of chromosomes contains either two “X” chromosomes in females, or an “X” and a “Y” in males (Cyr, “Chromosome Behavior…”). Thus, should a particular gene reside on the X-chromosome, females have twice the likelihood of having this said gene. For instance, the dominant gene that allows humans to perceive color resides on the X-chromosome. This means that if an individual possesses one or more dominant alleles (form of a gene) for this gene, he or she will perceive color because the color perception gene dominates the recessive color-blindness gene. On the other hand, if a person has only recessive alleles (either two recessive alleles or one recessive and one Y-chromosome) he or she will not perceive color because the recessive gene does not code for the necessary proteins. Hence, if a female (XX) possesses a dominant and recessive allele (a heterozygous genotype), she will perceive color normally. She could, however, pass her recessive (color-blind) allele to an offspring, thus making her a “carrier.” Consequently, if a male with the genotype XY has the recessive allele on his X-chromosome, he will not perceive color because he only possesses the recessive, non-functional allele. The science behind these genetic patterns can continue on indefinitely, but the point remains that males live at much higher risks for sex-linked diseases, many of which affect daily life far more than color-blindness.
Through the use of PGD, many sex-linked diseases could cease to affect humans everywhere. Diseases such as hemophilia, a life-threatening disease involving clotting factors, Becker muscular dystrophy, a crippling disease affecting protein production, and Duchene muscular dystrophy all follow a sex-linked pattern, and PGD can very easily reduce their rates of inheritance in the near future (Cyr, “Chromosome Behavior”). Consider the following: If a potential father exhibits a sex-linked disease, such as hemophilia, the disease results from a defect on his X-chromosome. Thus, he could seamlessly pass his Y-chromosome to the next generation, which would form a male zygote without any risk of his son inheriting the disease. Meanwhile, any daughter of his would certainly inherit the disease allele from his X-chromosome. However, nature never guarantees a son (or a daughter for that matter). Only through PGD can he ensure the implantation of a male zygote. And by using PGD to do so, he can save his child from hemophilia. Likewise, if a mother carries the recessive allele and the father does not exhibit the disorder, any female zygotes from these two parents have a zero percent chance of suffering from the disease (though they may carry the recessive, or disease-coding allele) because the father’s allele would dominate (Reilly 238). On the other hand, every male offspring would have a 50% probability of inheriting the mother’s recessive allele. Clearly, PGD’s sex-determination capabilities offer a distinct advantage when dealing with sex-linked diseases. Geneticists have already started using PGD for sex-determination, and because of decisions such as these, children of carrier or affected parents can still live normal, healthy lives.
As progress also continues with the human genome project, PGD will likely gain the ability to limit the transmission of other, more complex genetic disorders. Huntingdon’s disease, for instance, causes a patient to suffer from symptoms including dementia, loss of muscle control (known as chorea), mania, depression, and eventually death. The disease depends entirely upon one’s genome, and it follows a dominant, non-sex-linked (autosomal) pattern of inheritance. Therefore, no carriers exist, because anyone with even one allele for the disease will develop it (Reilly 86). In other words, regardless of whom a patient of Huntington’s may reproduce with, he or she has a one-in-two chance of passing this life-threatening allele on to his or her children. This probability, though, can decrease exponentially with the help of PGD and recent genomic discoveries regarding Huntington’s. Recently, scientists have essentially isolated the sequence of nucleotides (small bases that make up DNA) associated with Huntington’s, a discovery that could aid treatments for current patients and keep future generations from suffering. However, the latter may only occur with the help of PGD. If a Huntington’s patient wishes to conceive a child and he or she has both a recessive (unaffected) and dominant (affected) allele, scientists will soon have the ability to analyze the blastocyst’s DNA for this specific nucleotide sequence to determine if the child will suffer from the disease (Reilly 247). Should the blastocyst display the affected allele, the parents and medical staff would choose not to implant said embryo. Meanwhile, they could choose to implant a blastocyst that displays two recessive alleles, which would in turn develop into a healthy child. Discoveries such as these happen every day in the medical community, and while scientists continue to amalgamate disease-related nucleotide sequences into a “library,” more and more children will live disease-free. These changes have just begun, but they already have the power to save countless children from genetic diseases.
Though not fully isolated yet, genes tied to hundreds of other disorders may work with PGD to reduce human suffering across the globe. Nearly every disorder on the planet has some connection to genetics; therefore, by having the potential to manipulate the human genome, scientists should theoretically have the ability to “treat” everyone of these diseases (“Specific Genetic Disorders”). To clarify, scientists do not yet have the capability to insert and delete specific alleles from a genome. They do, however, have the ability to choose which parental alleles combine to form a zygote. Decoding the human genome could allow scientists to analyze a child not only for hemophilia and Huntington’s, but also for breast cancer, Tay Sach’s Disease, phenylketonuria, Marfan Syndrome, cystic fibrosis and countless other disorders. In theory, as long as one parent contains at least one unaffected allele (for recessive disorders), a child could live with a much lower, if not zero risk for any of these diseases. Obviously most disorders, such as cancer, have an environmental component, but skillful manipulation of the genome would undoubtedly reduce a person’s risk. As Peter Reilly alludes to in his book The Strongest Boy in the World, while the technology does not yet exist to analyze and predict the likelihoods for each disease listed, it does not mean that geneticists will not have the technology in the near future (Reilly 248).
Along with the potential to reduce human suffering, PGD also brings a risk of abuse. Even today, the scientific community encounters moral dilemmas related to the use of PGD. One hypothetical example involves a child suffering from a genetic disorder that doctors could only treat with tissue obtained from an unaffected family member. Could the family justify using PGD to have a child solely for the sake of saving their first-born? In 2000, the Nash family encountered this moral dilemma. When six-year-old Molly began suffering from Fanconi anemia (FA), her only chance for relief would come from the cells of her younger sibling, whom the parents would need to conceive using PGD and the in-vitro process (Reilly 244). FA causes bone marrow failure, usually leading to a form of leukemia, and it places patients at incredibly high risks for other fatal cancers. She needed the cells of a potential sibling because the only treatment involves the donation of bone marrow from a person with the identical gene pattern (“What is Fanconi Anemia?”). And so to save their daughter’s life, the Nash parents underwent the in-vitro and PGD processes to find an embryo with the identical bone marrow nucleotide sequence, but without the gene for FA. After locating such an embryo, doctors then implanted the blastocyst that would become their son. From his mother’s uterine wall, young Adam saved his sister’s life as doctors extracted his bone marrow to perform the transplant. Four years, later, both siblings live healthy, normal lives (Reilly 244).
Instances involving “savior siblings” such as this one offer another way for PGD to change the ways that we treat certain diseases. But should we do so? Can every parent justify the decisions made in the Nash case? Cases such as this exist for several diseases, but the question becomes: should parents use PGD to create a life for the sake of saving another life? No one has a clear-cut answer. Some argue that “savior siblings” will feel less valued when they learn their “purpose” in life. Others argue that any child would leap at the opportunity to save a sibling’s life, no matter the circumstances (Reilly 245). Regardless, issues over PGD such as “savior siblings” continue to evolve alongside the genetic technology.
When couples propose using PGD for purposes other than alleviating human suffering, it also PGD also breeds substantial conflict. Currently, the American Medical Association (AMA) Code of Medical Ethics condones the use of PGD to “prevent, cure, or treat genetic disease;” however, it does not approve of the procedure when used for “non-disease related characteristics or traits” (American Medical Association, qtd. in Reilly 240). But despite this guideline, what would prevent couples from predetermining their child’s sex simply based on preference? The AMA’s code of ethics may preclude doctors from performing such operations in the country, but what authority could stop couples from crossing into Canada to conceive a child? Just as PGD can easily determine an embryo’s sex to preclude the transmission of a gene for hemophilia, it can allow parents to have as many children of a given sex as they desire. But at what point does this become eugenics? In male-dominated societies, such as China, an imbalanced sex ration could push the population out of equilibrium. This of course would bring with it dire consequences.
Simultaneously, if scientists identify genes for athleticism or intelligence, what would stop parents from selecting those genes for their child? Again, the eugenics issue surfaces, yet many argue that these decisions have as much moral validity as using PGD for disease-related decisions. Besides, who could stop a couple from creating an “ideal” child if they feel that way? The answer lies in the future. Already, European nations have implicated certain legislation, yet the variation between nations causes trans-border procedures and increases the risks (Soini 309). In essence, the United States could learn from this debacle and enact federal legislation, or at least consistent state legislation, but this would require an increased understanding and awareness of the technology. As Jeffrey Kahn and Anna Mastroianna discuss in their report “Creating a Steam Cell Donor,” reproductive medicine currently remains badly regulated throughout the country, as the power rests in every state to independently regulate PGD (Kahn & Mastroianni 89). While states do not have enough legislation in place today, the necessary laws will undoubtedly come with time.
PGD will also engender conflict as part of the ongoing abortion and in-vitro debates. Given that not all zygotes created during the in-vitro/PGD process implant in the uterus, many groups assert that these zygotes undergo harm. Under federal law this constitutes a crime (Parens et al., qtd. in Kahn and Mastroiannai 89). Most people accept that this legislation results from the prevailing Catholic doctrine of “life begins at conception.” However, should legislation regarding the use of human zygotes for PGD supersede some of these laws, it may lead to more liberal policies regarding stem cell research, another potential life-saving technology.
In addition to possibly altering government policy, PGD might shift the way people consider the idea of reproduction. Catholic doctrine also condemns the separation of marital love and procreation, a perspective that, in theory, condemns the use of in-vitro fertilization and PGD (Reilly 240). However, if the prevalence of PGD increases dramatically due to its disease-prevention capabilities, societal acceptance may increase as well, even among religious groups. Hence, acceptance of the in-vitro process would also have to increase proportionally. Could this change, combined with greater public understanding of reproduction, not cause more of the population to believe that life can only sustain itself after implantation as opposed to conception? No one knows for certain, but speculation such as this demonstrates how drastically PGD might change the way our society thinks about conception and reproduction.
Despite its newness in the medical community, PGD has already begun to impact families around the world. According to B.M. Dickens, PGD has helped thousands of families and children in countless ways since its first documented usage in 1989 (91). The most famous instance of this comes from the Nash family, who used PGD to create a son with the bone marrow to save their daughter (Kahn & Mastroianni 81). And because of PGD, Molly Nash now lives disease-free. Other examples include parents who used PGD to have a child without Down’s syndrome or other genetic disorders. By 2004, scientists had analyzed and implanted nearly 1,000 children who have grown up normally thanks to the technology (Verlinsky, et al. 294). And during the past ten years, even more children have had the opportunity to live without high-risk alleles. Yesterday scientists looked as the sex of an embryo to see if it would suffer from sex-linked diseases. Today, they analyze embryos for Huntington’s chorea and colon cancer, two diseases that never even received consideration when PGD first became available (Reilly 247). As for tomorrow, no one can say for certain what geneticists will analyze, but it will undoubtedly change the world.
Technology has advanced far faster than almost anyone expected, and society holds a responsibility to develop its knowledge with that technology. More and more people will soon start having children through means that did not even exist for prior generations; we must prepare for this shift. And while some groups completely reject the technology, it may befit society as a whole to take a more moderate approach to the issue. As referenced earlier, Congress and state legislatures have not yet enacted the legislation necessary to regulate this development, but they will soon have to. And so as humankind’s most fundamental task evolves into a process conducted not in utero, but instead in laboratories, it may behoove us all to prepare today for the debates, the controversies, and most importantly, the disease-free lives of tomorrow.
Cyr, R. 2002. “Chromosome Behavior and Sex Chromosomes.” In, Biology 110: Basic concepts and biodiversity course website. Department of Biology, The Pennsylvania State University. http://www.bio.psu.edu/
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Kahn, Jeffrey P. & Mastroianni Anna C. “Creating a Stem Cell Donor: A Case Study in Reproductive Genetics.” Kennedy Institute of Ethics Journal. 14.1 (2004): 81-96. Johns Hopkins University. Web. 2 December 2014.
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