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Gene Therapy

Introduction

Human gene therapy, also referred to as genetic engineering, is a new and exciting experimental treatment that involves transplanting normal (or healthy) genes into human beings who suffer from severe diseases. Gene therapy has been divided into two categories: somatic cell and germ line. Somatic cell gene therapy focuses on treating all the cells within the body, with the exception of the reproductive cells. It is generally accepted as a conventional medical therapy and would result in correcting a genetic defect in the non-sex cells of the person. Germ line gene therapy, on the other hand, would treat cells of the reproductive tissues of a patient, which would result in a genetic correction in the patient’s offspring (preventing further inheritance of a trait). Because future generations would be affected by this method of treatment, there has been an ongoing discussion as to whether this approach is ethical. Therefore, the federal government is not funding germ line gene therapy at this time.

The human body is made up of approximately 50 trillion cells. Within these cells are genes (made up of a chemical called DNA), which contain the information as to what the cell should do and how it should work. There are about 100,000 genes in each cell of the human body. Although the genes are the same in every cell, each type of cell reads only certain genes. For example, a muscle cell works differently from a skin cell.

If the information of a particular gene contains a mistake, the gene may not function properly, which can sometimes lead to a severe genetic disease. Therefore, the idea behind gene therapy is to insert normal genes with correct information into the DNA of the cells that contain malfunctioning genes. This is known as "gene insertion." When inserting normal genes, it would allow the cells to function properly and might reduce or eliminate the signs or symptoms of the disease.

 

Methods of Gene Therapy

One of the methods that is being used to insert genes is to link the gene to a virus that has been crippled and rendered harmless. This virus (also known as a vehicle) has been deliberately altered so that it carries genes into the cells but cannot escape. The process begins with removing the affected cells that need treatment from the patient’s body. Then, the virus is used to carry the correct genetic information to the affected cells. Once the cells have been given the desired new genes, the cells are returned to the patient’s body.

A new approach, developed by Dr. Clifford Steer and his colleagues at the University of Minnesota Medical School, has been termed chimeraplasty. This technique allows genetic material to be conveyed to the cell without using viruses. This new method can change a cell’s DNA with precision and without the risk of infection posed by viruses. So far, chimeraplasty has only been used on rodents; clinical trials are expected to begin on patients sometime in 1999. In addition, this method is limited to liver cells, however, Dr. Steer believes that one day, it will also become useful for nervous system cells, stem cells, kidney cells, and muscle cells.

 

Treatment

The first successful gene therapy treatment on a human was performed in 1990 on children with Adenosine deaminase (ADA) deficiency (also known as "Boy in the Bubble disease"). The deficiency is caused by inheriting two copies of the defective ADA gene, resulting in almost the complete failure of the immune system and early death. Using a genetically-altered mouse retro-virus, a properly functioning ADA gene was spliced and delivered to the T-lymphocytes. As a result, the children had tremendous increases in their immune functions and they even grew tonsils.

More than 250 somatic cell gene therapy research trials are currently underway. Many of the trials are focusing on diseases such as cancer, cystic fibrosis, phenylketonnuria (PKU), urea cycle disorders, Duchenne muscular dystrophy, and Gaucher disease. However, none of these conditions have been cured yet by gene therapy.

The most promising use of gene therapy will be to treat single gene defects that cause significant disabilities and cannot be treated by any other method. The current approaches to gene therapy cannot be used to treat some chromosomal abnormalities such as Down syndrome. The reason for this is that though it is known that an extra chromosome 21 causes Down syndrome, scientists have not yet identified the specific number and location of the genes involved. In contrast, however, is the treatment of fragile X syndrome, where the gene causing the disorder has been identified (although more research is necessary to determine the function and control of the gene before gene therapy is considered as a treatment option).

 

Medical, Ethical, and Religious Concerns

As with any type of medical treatment, human gene therapy does have its risks. For example:

Gene therapy raises ethical issues in regards to the quality of life of people with disabilities. Some people with disabilities have communicated that their disabilities are not diseases and, therefore, should not be treated. These people believe that advocating for a cure indicates that their lives do not have value just because they are disabled. In response to these concerns, The Arc, a national organization on mental retardation, has been asking their members to complete a questionnaire based on the following statements:

The results were very supportive of the use of gene therapy. Almost 90% of the members questioned feel that gene therapy should be pursued and would not devalue the life of an individual with a disability.

Another issue causing extreme concern involves eugenics, a "movement devoted to improving the human species through the control of hereditary factors in mating." This is a term that is used to describe selective breeding of people with more desirable traits. In the early 1900's, individuals with mental retardation, mental illnesses, alcohol addiction, and epilepsy were forced to be sterilized in the hopes of eliminating future generations with these conditions. In addition, the movement targeted other individuals who were also considered less desirable. Therefore, one of the fears is that gene therapy will reintroduce the eugenics movement which may, once again, cause some type of coercion for people with disabilities.

Furthermore, there are religious issues to acknowledge. Several different religions have a concern regarding gene therapy in that it is equivalent to playing God and that it interferes with nature. They argue that God created man in his own image, and for man to change himself implies that he can dismiss the power of God and make himself better.

 

Conclusion

Gene therapy could redefine the practice of medicine in the next century. The very concept of altering ones genetic makeup when drug treatment is not an option is phenomenal. Gene therapy is expected to one day cure 4,000 known genetic disorders, as well as heart disease, cancer, arthritis and other illnesses. Scientists disagree on how many more years it will take to offer gene therapy as an effective treatment, however, most of them believe that gene therapy is "on track to be the most powerful curative and diagnostic tool ever."

For more information on gene therapy, please visit the following web sites:

 

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