The only method of therapy currently available for humans, however, is gene addition. Technical breakthroughs are thus needed before gene replacement or repair becomes practical.
Although many other technical hurdles face germ-line gene therapy, like minimizing risks of insertional mutations and inadvertent production of chimeras, the highest by far is the unavailability of replacement or repair technologies.
Germ-line gene therapy is carried out in gametes or preembryos. This presupposes a reproductive process that involves in vitro fertilization IVF for identification of a defective gamete or preembryo.
Only at-risk couples willing to use such procedures will benefit from germ-line gene therapy. Even if IVF is used, however, there are questions about why gene therapy would be pursued.
If a potential disease is identified in a gamete, then one can avoid the disease by simply discarding that gamete. Any medical procedure involves risks of harm, and there seems to be little warrant for such risk, if the disease can be avoided altogether by choosing not to proceed with a particular gamete. If a disease is identified in a preembryo, which possesses the full complement of 26 chromosomes, the issue is more complex. Those involved in the research related to germ-line gene therapy regularly create and destroy embryos as a part of their research.
For those who do not find such destruction of the preembryo problematic, the same question raised about gametes is relevant: why would a defective preembryo ever be implanted? Those who consider it wrong to destroy a preembryo have a stronger reason to pursue gene therapy. However, such individuals would strongly criticize a research process that perfects the techniques of germ-line gene therapy by the use of extensive nontherapeutic research on embryos.
Moreover, those who object to destruction of preembryos usually also reject the IVF procedures used to create and test embryos. They would thus be unlikely to avail themselves of the technology for gene therapy. Such concerns raise questions about why research in germ-line gene therapy should be pursued at all. If not for the sake of treating diseases in particular individuals and their progeny, then it may be for the sake of developing the science needed for enhancing genetically determined characteristics; that is, for pursuing genetic enhancement.
Scientists cannot, therefore, neatly separate the two research agendas, although they could separate the practices, once the technology was developed. If enhancement is illicit, an issue which we consider in the following essay, then reservations about enhancement may extend back to germ-line gene therapy, thus making the somatic vs.
Other arguments against permitting germ-line genetic research are related to the possibilities of genetic enhancement the new technology makes possible. Totalitarian governments, for example, may produce superior humans who will reduce the nonenhanced to menial servitude. There is no reason to think that genetic technologies would be useful to a totalitarian dictator interested in dominating populations, when they are compared with other biological, psychological, and social means for such domination.
A potentially more likely scenario is gradual exacerbation of existing class distinctions, because individuals with financial means might more easily avail themselves of gene technologies. Gene therapy is expensive, and its association with IVF makes it unlikely, in the near term, that costs will be covered by insurance schemes that are moving in the direction of more sparse types of coverage. People of means may thus have better access.
This problem is not unique to genetics. It is found in other economic sectors, and technology that is initially expensive usually becomes increasingly available to all people; computer technology is an example. Much of the cost of gene therapy, however, is associated with the labor-intensive character of the highly skilled procedures, making rapid lowering of costs unlikely in the near future.
Automation may reduce costs dramatically over longer time periods. Nevertheless, short- term differential access has raised legitimate concerns about the use of public funds to advance such research. Potential unintended consequences are part of the price of virtually all advances in medicine, but gene technology introduces the prospect of seemingly new kinds of harms. The human genome underlies species design, so the incidental elimination of important but unappreciated function may lead to decreased species fitness.
All medical interventions affect human evolution by extending lives that would otherwise end, but germ-line modifications may affect evolution to a greater degree and in a shorter time frame than other interventions. Moreover, conventional medical interventions risk harm to individual subjects, while germ-line modifications pose risks to future generations, as well. Some deleterious consequences may not become manifest in the first generation.
This makes germ-line gene therapy in some ways more akin to a public health intervention, rather than a traditional medical one. Other considerations favor pursuing germ-line gene therapy research. A persuasive medical reason is that this kind of therapy may be the only way to treat certain problems.
For example, to prevent the expression of certain genetically determined tumors, like retinoblastoma, it may be necessary to reach every individual cell that could initiate growth of a tumor. As noted above, though, simply discarding cells that contain the tumor gene would completely avoid such illnesses. Diseases like cystic fibrosis or diabetes could potentially be treated with somatic cell gene therapy, but parents may, for good reason, want to relieve their children of the necessity of undergoing such treatment or of the responsibility of transmitting unwanted harmful genes to their own children.
From a public health perspective, efficient prevention of disease is an important social value, as is conservation of future health care resources. Germ-line gene therapy may lead to both of these outcomes.
Conclusion Somatic cell gene therapy research is relatively uncontroversial, but the debate about germ-line genetic research has not been resolved. Perhaps the strongest argument against an extensive ban on research is that this technology cannot be eliminated. If research is banned in the United States, it will be done elsewhere, with fewer resources to responsibly address the consequences. The science is here, and we must anticipate its development.
The key question is whether and how to regulate it so that basic ethical norms are not violated and harms are minimized. Legitimate concerns regarding the harms that may be associated with gene therapy must be identified and publicly discussed, even as the beneficial uses of gene technology are sought. Gene technologies embody the paradigm of the potential benefits and dangers of modern science.
They provide humanity with unprecedented power over its own nature. We can only hope that, as the body of genetic knowledge grows, we will have the wisdom to use it constructively. Mulligan RC: The basic science of gene therapy. Science 2. Progress toward human gene therapy. JAMA 19 3. Walters L, Palmer JG. Nature Medicine 1 10 , 5. Zabner J. Wadsworth SC. Smith AE. Welsh MJ. Adenovirus-mediated generation of cAMP-stimulated Cl- transport in cystic fibrosis airway epithelia in vitro: effect of promoter and administration method.
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