Ten years ago researchers from the U. S. , Britain, France, Germany, Japan and China sat down and began developing the most important map ever made. Instead of roads and landmarks, this was a map of letters. It was a rough map of the 3 billion letters of genetic instructions that make us who [we] are (First). On Monday, 26 June 2000, the researchers announced that the map of the human genome was complete. On 26 June 2000 the news of the completion of the human genome was on all the major news wires, televisions and newspapers. What does it mean though?
How will this help mankind? One area to which this knowledge can be applied is in the area of gene-therapy. Gene-therapy is now being tested to treat and cure some common genetic disorders. Like all new research, gene-therapy is the center of much controversy. A discussion of genetic disorders and current prevention methods is enlightening. In addition one must understand what gene-therapy is and how it is being used. In order to understand how genetic diseases are formed, it is important to understand how genetic traits are passed on from one generation to the next.
An individuals genes carry the codes needed to make proteins to perform specific functions throughout the body. These genes are encoded into our DNA. A gene is made up of alleles. These alleles are the specific traits that each person possesses, everything from eye color to physical size. Some alleles are dominant, such as the allele for brown eyes, while others are recessive, such as blue eyes. During reproduction the alleles from both parents are combined and copied within the fertilized egg. These genes may sometimes sustain damage or could be copied incorrectly.
When this happens it is called a mutation. Mutations occurring in this manner are seldom for the better. Fortunately, the human body contains cells that police the genes and correct most damage they encounter. Mutations are very rare in human beings. Most mutations occur in recessive alleles and are not passed on from generation to generation. In some cases the mutant alleles are found to be more common, and the harmful effects become known as genetic disorders (Johnson 178). Although genetic disorders are rare, some have been found to be more common than others.
One such disease is Hemophilia. This disease occurs in 1/10,000 Caucasian males. Hemophilia is a mutation of one of the proteins used in the blood clotting process. When a blood vessel is cut or ruptured, a dozen or more proteins will go to work causing the blood to clot. If any one of these proteins fails to do its part, the clotting process will be slow or non-existent. This can cause an individual with a small cut to bleed to death. Another more common genetic disorder is Sickle-Cell Anemia. This is a recessive disorder in which afflicted individuals have defective molecules of hemoglobin.
Hemoglobin is a protein within red blood cells used for carrying oxygen. The mutation causes the hemoglobin molecules to stick together forming a sickle-shaped cell. These cells have trouble moving through the smallest blood vessels and tend to build up, blocking the vessel. As stated earlier, most diseases are caused by recessive alleles. This means that both parents would have to carry the recessive allele in order for it to be passed on to their offspring. There are, however, a few genetic diseases that are caused by dominate alleles. One such disease is Huntingtons.
Approximately 1 in 24,000 individuals develop this disease. This disease causes progressive deterioration of brain cells. Unlike recessive genetic disorders, all individuals carrying this allele will display the disorder. While researchers are still working on a cure for genetic disorders, there are a number of ways the physicians are able to prevent some of the diseases. One way that scientists and physicians are able to prevent the spread of these horrible diseases is through genetic counseling. Genetic counseling is a process of identifying whether a given disease is likely to recur in a family.
There are a number of variables that will help the counselor determine if the disease is likely to recur. These variables include such things as family history and the characteristics of the disease itself. Genetic counseling is recommended for couples who are planning to conceive and have already had a child with a genetic disorder and for couples with one or more relatives that have a genetic disorder (Management 737). Genetic counseling only identifies the risk of the disease recurring. Once the risk is identified, the couple is faced with some very tough choices.
Couples usually have four options to chose from if they are at risk. The first choice is to just accept the risk and conceive normally. A second choice is to use artificial conception using a strangers sperm. This is only effective if the husband is the primary carrier. A third method is selective abortion. This involves aborting any embryos that can be determined to carry the disease. The final and most effective method is to decide against reproduction (Management 737). Another form of prevention is called prenatal diagnosis.
This method involves performing genetic testing on the amniotic fluid that surrounds the fetus. This fluid contains skin and mucus cells from the fetus itself. The genetic testing is done during the 15th to 17th week of the pregnancy to determine if the fetus has a genetic disorder passed on from the parents. While this method can often relieve the burden of anxiety, if it is negative, it can also create great emotional trauma if the pregnancy needs to be terminated (Management 737). Scientists at Cornell University have developed a new procedure called preimplantation genetic diagnosis.
This procedure allows scientists to determine if embryos fertilized and grown in a lab have inherited a particular gene. Only embryos without the defect are implanted in the uterus, thereby eliminating the chances of creating offspring with the disease (Preventing). The final preventative measure utilized is genetic screening. Genetic screening has the potential to decrease the impact of genetic disorders through a systematic search for persons with a particular genotype in a defined population (Management 738). Certain populations of individuals are more prone to different types of genetic diseases.
Illustrations of this include Sickle Cell Anemia among people of African decent and Crigler-Najjar Syndrome among Amish and Mennonites. Genetic screening would involve identifying individuals within these groups who are carriers of the disease. There are, however, a number of problems involved with genetic screening: invasion of privacy, gene discrimination, and the loss of self-esteem among carriers (Management 738). While genetic counseling can prevent parents from producing children with genetic defects, it is only the beginning.
Since 1990 researchers have been experimenting with a process known as gene-therapy. Gene-therapy attempts to correct mutated genes instead of just discriminating against them. Currently researchers are attempting this by injecting the correct form of the gene into a virus that is then introduced into the body. The virus finds its way to the cells and leaves the corrected copy of the gene in place of the mutated or missing gene. Through genetic testing and gene-therapy, scientists believe that someday they will be able to eliminate these life threatening genetic disorders (Wheeler).
One of the major drawbacks of gene-therapy is the method used to introduce the corrected gene. Current trials are using the Adenovirus-Associated Viruses, also known as AAVs, as the transport method. These are small DNA viruses that can deliver genes to many tissues (Bradbury). After a recent death during a gene-therapy trial involving AAVs, it was revealed that there have been 691 instances of adverse effects in the 93 gene-therapy trials using this virus (Nash). Another drawback of gene-therapy concerns the subjects that are being used.
Researchers believe that fetuses are the best candidates for gene-therapy because of their rapid cell division. This rapid cell division allows them to take up the new genes more easily (Wheeler). Anytime fetuses or infants are involved in scientific research there is likely to be controversy involved. It is important to remember, however, that many of the genetic diseases are fatal. Without this type of research many of the fetuses involved would never have a chance at a normal life. Since 1990 ninety-three gene-therapy trials have been accomplished.
Some of these trials have had very positive outcomes, while others have ended in tragedy. As with all research, some of these trials have set milestones in the area and others have put up roadblocks. In one study at Cornell University scientists were able to allow parents who both carry the gene for sickle-cell anemia to bear twins free of the genetic disorder. To accomplish this, researchers fertilized and grew seven embryos in a lab. DNA testing was then accomplished on the embryos, and three embryos were found to be completely free of the defective gene.
They were then implanted into the uterus of the woman. Nine months later she gave birth to a healthy set of twins (Preventing). While this is more of a discriminatory process rather than true gene-therapy it was one of the first successful attempts to eliminate a genetic disease within a family, and it opened the door to future research. In 1999 gene-therapy faced a major set back when 18-year-old Jesse Gelsinger, a research volunteer, became the first person to die as a direct result of gene-therapy.
Jesse was undergoing gene-therapy at the University of Pennsylvania for a rare metabolic disorder he had suffered from since birth. Gelsingers death has been linked to the adenovirus used to introduce the corrected gene. His death prompted the Food and Drug Administration to shut down all gene-therapy research at the university (Nash). As the scientific community was recovering from the Gelsinger death reports began circulating that a team in France had successfully used gene-therapy to cure severe combined immunodeficiency in two infants (Nash).
This is the same disease that was portrayed in the movie The Boy in the Plastic Bubble. The disease is caused by a missing gene responsible for the production of immune cells. If left untreated the condition usually results in death within two years (Guterman). The gene-therapy trial involved introducing a normal copy of the gene into the infants. The two infants have now been living out of isolation at home for eleven months without any side effects or need for any additional treatment.
A third patient has shown similar progression for the past four months since the gene transfer (Dobson). Successful trials such as the one in France show us that gene therapy has come a long way in its ten years. Gene-therapy is only the beginning. With the completion of the Human Genome Project, new doors have been opened for safer more advanced research. Micheal Blaese, Chief of Gene Therapy for the Human Genome Project, is already working on a new procedure that will repair faulty genes through molecular microsurgery.
This procedure corrects small letter code errors in the DNA codebook. Gene repair has the potential of treating a much broader variety of genetic disorders than is possible with current treatments. The first gene repair trial on a human being was originally scheduled for spring of 2000. Unfortunately, that date has been pushed back to 2001 (Wadman). Genetic disorders have plagued our society since the beginning of time. Through research and gene-therapy scientist may eventually be able to put an end to them. Scientific discoveries and medical advancements do not come without risk though.
It is important to have a good understanding of the risks involved as well as the possible benefits that can be achieved. Educating the general public in this area will help. Not only does gene therapy have the ability to save live, it also has the ability to change mankind itself. Anytime a person is given the ability to alter human life there will be controversy involved. It is up to society to ensure this ability is not abused. The medical community needs to ensure the technology is used for the benefit of all and not the advantage of one.
