Germ line gene therapy is a form of disease treatment where genetic alterations are made at the germ line, or pre-embryonic stage, to sperm or egg cells. This is as opposed to the traditional somatic approach, where an attempt to treat disease is done at a genetic level in fully mature organisms. Though germ line gene therapy is a more effective treatment, it carries with it a variety of controversial ethical and societal concerns.
Somatic gene therapy has been practiced since the early 1990s with very limited effectiveness. In somatic gene therapy, malfunctioning genes are replaced or genetically enhanced in a patient with the goal of treating the targeted gene. These treatments have often proven to be ineffective or temporary. The fundamental advantage to germ line gene therapy is that the genetic change is carried forward into the embryo as a permanent and natural part of development. Such genetic changes are irreversible, and they can then be passed on by the subject to his or her offspring.
Both forms of gene therapy generally use the same proven method, or vector, for inserting new genetic instructions into cells. Viruses, which are otherwise harmless to the body, are used as transport mechanisms. Part of their genetic structure is altered to carry the desired gene, and they are then inserted into the host, where they integrate their DNA into the cellular structure of the DNA of host cells. They reproduce along with the cells of the host, thereby spreading the altered gene throughout the body.
Where somatic treatments fail is in how this new genetic material is adopted by the body. Often there are immune responses, side-effects from the presence of the virus, and damage to the cell that can lead to mutation and cancer. As well, many diseases are often the result of several genetic weaknesses which cannot be treated by correcting just one gene. Germ line gene therapy bypasses most of these problems while creating new ones of its own.
Successful treatment with germ line gene therapy is likely to have no immune response at all. Also, it is easier to make alterations to sperm or egg cells than it is to try to treat a complex and established genetic disorder in an adult. By contrast, germ line gene therapy, if flawed, can be much more harmful to the embryo than an adult, resulting in deformity or death.
Ethical issues arise as well where it becomes possible to use germ line gene therapy to alter the fundamental characteristics of an individual. Such alterations can occur in sex, height, intelligence, skin color, and so on. On a larger scale, this could become a eugenics program, manipulating entire populations to weed out undesirable traits.