In recent years, the introduction of gene therapy has generated excitement and controversy in society. People affected by rare diseases, have now been given the chance to live their lives again. There are a number of scientific and ethical issues that have yet to be resolved, before it becomes a substantial treatment method for all who need it.
Frightening though it may be, death is an inevitable consequence of birth. Unfortunately, there are a few individuals who have a defect in their genes, which numbers their days, right from the moment they are born. Science and technology have evolved to the extent that it may be possible to overcome the faulty gene with a genetically engineered normal gene. There are a number of limitations and benefits of this treatment, but overall, gene therapy promises a cure for previously incurable and debilitating diseases like Severe Combined Immuno-deficiency (SCID), haemophilia, and muscle dystrophy. However, the therapy is still in its infancy and faces significant hurdles, before it can become a common everyday cure.
Scientific Issues of Gene Therapy
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Gene Therapy and How It Works
Genes form the blueprints for making the proteins from which our body is made. They lie within the chromosomes in a cell nucleus and are made up of DNA. Normally during cell replication, they are copied faithfully. Sometimes mistakes happen in the copying process and the order of DNA molecules is altered, namely a genetic mutation. Then, the proteins which the gene was responsible for, gets altered and cannot function properly. The individual suffers a "disease". In the past, we were unable to rectify this defect. Gene therapy offers a way to overcome the problems by inserting a normal copy of the gene in the cell for synthesising the correct protein.
In gene therapy, segments of DNA are inserted into the cell (refer to Figure 1) as naked DNA or as part of a vector (Anon, 2011). Vectors are often defective viruses, altered not to cause disease, but to deliver the gene, by infecting the cell (Panno, 2005, p.29). The type of virus used as a vector depends on the disease and nature of the cell that is diseased. If the diseased cells are rapidly dividing, viruses called retroviruses are used to genes into the DNA of the cell. This method has been used to cure SCID, a disease of rapidly multiplying immune cells which makes people unable to fight infections and lead to their deaths. If the diseased cells are somatic cells that do not multiply rapidly, then adenoviruses can be engineered to deliver the gene into the cell. The introduced gene will be separate from the nuclear DNA, and will produce proteins which will overcome the defective gene (Anon, 2011). A fatal liver disorder from ornithine transcarbamylase deficiency, has been treated using the adenovirus vector. Herpes simplex virus vectors are used to transfer genes into the nervous system. Naked DNA can be injected directly into diseased muscle cells and liposomes can be used to transfect cells that can be taken outside and infused back into the body.
Figure 1: How Genes Are Inserted and Delivered to the body (Anon, n.d)
Dr W. French Anderson and Dr Michael Blaese completed the first gene therapy trial in 1990 on a four year old girl to treat adenosine deaminase deficiency, which made her vulnerable against infections (Anon, n.d).
Gene therapy has been used in clinical trials for other inherited diseases like SCID, ornithine transcarbamylase deficiency, haemophilia, sickle-cell anaemia and congenital blindness (Kelly, 2007, p.3). Gene therapy is being developed to treat non-inherited diseases, like prostate, head and neck and pancreas cancer, neuro-degenerative diseases such as Parkinson's disease and Huntingdon's Disease as well as infections like HIV, hepatitis and influenza. (Anon, 2011).
Scientific Limitations of Gene Therapy
Despite the novelty and promises of this mode of therapy, the first death due to gene therapy happened in 1999 during the experimental trials, when 18 year old Jesse Gelsinger underwent therapy for Ornithine transcarbamylase deficiency. The adenovirus vector that enclosed the gene was given at an extremely high dosage and Jesse died from the immune reaction that followed (Anon, 2009).
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A detriment of this type of technology is that there is a lengthy process involving the insertion, delivery and activation of genes and these may go wrong. The insertion of the single gene to the right cell in the midst of the several million cells needs high accuracy. It must be activated, to release the "new" protein to the rest of the body. If the new gene is delivered to the wrong cell, the patient is at a high risk of illness and consequently, perhaps even death.
Another issue that arose quite recently is that a gene may be integrated into the wrong section of the DNA. For the treatment to be successful, an inserted gene has to be incorporated into the cell's genome, which should optimally last for a long time (Cullen, 2011). If the attached gene disrupts the function of another crucial gene, new diseases may arise in the future. Gene therapy for people suffering from SCID involved the incorporation of a "gamma c" gene into the immune system. Although the disease was treated, some people later on developed leukaemia, because the gene was integrated into the wrong part of DNA.
Sometimes even if the gene vector is able to carry the gene into the correct cells, the body's natural immune system can fight off the viral vector. If this occurs, the patient may suffer severe damage to their health, and even death as was seen in the case of Jesse Gelsinger.
If the therapy involves using a retrovirus to carry a gene into the somatic system (non-reproductive system), the retrovirus integrates itself into the cell's DNA. If the retrovirus, by accident gets incorporated into germline DNA, then a new hereditary disease could manifest, being passed on from the mother to a baby. If the new gene integrates into a cell growth gene (an oncogene), it could potentially block cell growth, or even make cell growth excessive, as in cancer.
The Scientific Solutions to Gene Therapy issues
Conceptually, it should be easy to insert the gene if we had the perfect vector, or carrier. However, there is no "perfect" vector. We could choose a virus that has little or no response from the immune system (Anon, 2007). Genes can be inserted into nanoparticles to deliver them to the correct place of the body, to bypass the immune system. We could avoid retrovirus' and use other viruses- for example the adenovirus (the common cold or flu virus) which doesn't become incorporated into your DNA, and isn't involved in the cell division process.
Ethical Issues of Gene Therapy
Ethically, a major debate with gene therapy, would be whether it should be used, not just for treating diseases in the future, but for other reasons - like altering our own and our children's physical and mental characteristics? Obviously, the answer should be no - society shouldn't pay so that someone can change the colour of their eyes from black to blue- this is totally unethical.
Another debatable question is, "Who should have access to Gene therapy?" Undoubtedly, everyone deserves access to this treatment. But this would mean that the gene therapy (which is incredibly expensive to install and use), would require monetary support from public health services. This means that instead of perhaps three thousand people getting a vaccination, one person gets treated for SCID or another rare disease.
Physical Limitations and Benefits of Gene Therapy
Despite limitations and the potential for harm, gene therapy has its benefits. People suffering from rare diseases can potentially be 'cured'. It opens the door for creating more genetic technologies, perhaps those for treating the more common diseases, such as diabetes. Gene therapy has also helped to increase our understanding of the gene and its structure, which will pave the way for further advancements. A disadvantage of gene therapy is that it cannot treat polygenic diseases, such as high blood pressure and diabetes. However, if scientists have been able to understand the workings of replacing one gene, there is no doubt that towards the future, gene therapy will evolve to treat polygenic diseases.
Impact on Society
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Scientists, who are trying to treat diseases and enhance their own knowledge, ask for donations from society to keep gene therapy continuing. Gene therapy is only a treatment method for those suffering rare diseases. Those with common diseases, or multiple genetic defects, do not benefit. However, society has generally grasped the idea of gene therapy and supported it. The concept of helping extremely sick people with rare diseases that has no cure, has generally been the motivation for donating to this new therapy.
Overall, gene therapy has revolutionised science. Many people have benefited and hopefully others will benefit from this type of treatment in the future. Although they may be a small percentage of our global population, people suffering from these genetic diseases deserve the chance to have a fulfilled and happy life.