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Gene-Therapy: How Will It Change the Future of Genetic Disorders

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Brad Miller

Ms. Cheryl Weatherly

English Composition and Research

2 July 2000

Gene-therapy: How will it Change the Future of Genetic Disorders

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 individual's 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 Huntington's. 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 stranger's 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



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