The Genetic Screening Debate
by Kim Rauser
Within the past thirty years, researchers have found strong evidence linking genes and disease. The development of predictive genetic tests followed shortly after the isolation of certain candidate genes. Although predictive genetic screening is only available for a handful of diseases, its effects and ramifications have become hotly debated issues in a wide range of areas, from government to religion. The debate began in the 1993 when researchers isolated the BRCA1 gene, which is associated with increased risk of developing breast and ovarian cancer. The discovery of this gene led to excitement and speculation of developing a predictive genetic test to identify those women at risk for these cancers. In this paper, I will first describe the biology of genetic testing, and then discuss the pros and cons of predictive genetic testing.
Before we start discussing how genetic tests are developed, let us discuss how genes can trigger disease. A sound body requires the action of many proteins working together. For a protein to function properly, an intact gene must encode for that specific protein. A mutation describes a gene which has been changed. The most common type of mutation is a single change of a nucleotide of DNA. Other types of mutations include the loss or gain of a nucleotide and the disappearance or multiplication of long segments of DNA. Mutations can have three effects: beneficial, harmful, or neutral. Mutations are beneficial if the fitness of an individual is enhanced. Harmful mutations can either slightly alter a protein, where the protein may still minimally function, or they may totally disable a protein. In this instance, the outcome is not only based on how a mutation alters a proteinís function, but on how important the protein is to the body (Understanding Gene Testing).
Since we have determined how genes can trigger harmful effects in the body, we can now examine how scientists look for specific genes that cause diseases. Scientists, looking for a diseased gene, study DNA samples in individuals where the disease has been present in the family for many generations. They look for specific genetic markers, which are DNA segments that are identified in individuals with the disease, and not identified in healthy individuals. Scientists then narrow down the area of DNA by mapping a gene. If a disease gene is mapped to an area, then the genelike sequences become candidate genes for a specific disease gene.
The opposite may also result; the expression of sequenced genes in the tissue may suggest a disease gene. If scientists can determine the map position of a known disease gene, than the unassigned genes in that region may be candidate genes. Once candidate genes are selected, scientists then look for mutations in those genes. They can identify these specific regions by constructing DNA probes, which are single strands of DNA that line up with parts of a known gene. The probe, tagged with a radioactive atom, binds to the complementary bases. The area that the probe binds to will light up, allowing scientists to carefully examine that specific piece of DNA for any mutations. Scientists follow the previous steps to develop predictive gene tests (Understanding Gene Testing).
Predictive gene tests will tell an individual whether or not they have a disease-related mutation. An inherited mutated gene is carried in the reproductive cells. Therefore, the mutated gene will be present in cells throughout the body. Predictive gene tests can detect the mutation in white blood cells. If the mutation is present, the person must be told that a variety of factors will determine if the disease will develop. Most individuals who carry the familial adenomatous polyposis gene will ultimately develop colon cancer. On the other hand, women carrying the BRCA1 mutation have an 80% chance of getting breast cancer by the age of 65. Theses women also have a 20% chance of remaining free from breast cancer throughout their lives. Even those individuals who donít have an inherited mutation are still at risk for diseases, because other factors are involved.
Predictive gene tests are available for a number of diseases at the present, and many more are currently being developed. Diseases like Tay-Sachs and cystic fibrosis now have predictive gene tests. Within the family of cancers, genes have been found for 1) retinoblastoma, a childhood eye cancer, 2) Wilmsí tumor, a kidney cancer which attacks children before the age of five, and 3) Li-Fraumeni syndrome, which attacks children and young adults with an assortment of cancers. Recently, gene mutations have been linked to colon and breast cancer. Inherited forms of these cancers account for 5-10% of all cases. Although this number appears low, an estimated 1 in 300 women carry inherited mutations of the breast cancer gene. According to experts, this estimate also pertains to colon cancer cases. Most individuals who develop colon or breast cancer donít have inherited gene mutations. Rather, these individuals acquire mutations, which lead to cancer.
Although other genetic mutations have been identified before BRCA1 and BRCA2, it wasnít until their discoveries that much of the public began to take notice of these scientific breakthroughs. Scientists have high hopes for the results of the discoveries of these two genes. They hope that theses new genes will 1) increase the understanding of deadly cancers, 2) lead to effective therapies, and 3) identify those individuals at risk (Kahn 1996). In January of 1996, OncorMed, Inc. offered the test for the detection of the BRCA1 gene to consumers. Itís been almost two years since this predictive test became available to the public and since that time other tests have become available. These predictive gene tests have prompted a public controversy. Should genetic testing be made available to the general public? Why or why not? Letís take a closer look at the arguments from both sides.
The proponents are up first. These individuals believe that persons from high risk families can gain many benefits from knowing whether or not they carry a genetic mutation. For instance, a negative test that is strongly predictive can reassure a person and provide relief. A negative test can also eliminate the need for continued checkups and tests, like a colonoscopy, which is routine for individuals from high risk families. Proponents also point to a number of benefits from positive test result. 1) It relieves uncertainty, 2) it allows a person to begin making decisions about the future. If the test indicates that a person will definitely develop a disease, the person can begin to prepare for that time. 3) Under the best circumstances, a positive test result can lead to counseling and intervention to help reduce the risk of developing that disease. For example, the earlier that colon cancer is detected, the greater the chance of survival. 4) A positive test warns a person to continue checkups, and to maintain or begin to engage in a healthy lifestyle (high-fiber, low-fat diet, and regular exercise). 5) A positive test result gives the person the option of having surgery to remove that organ that is at risk for disease (Understanding Gene Testing).
Opponents to predictive genetic testing point out many problems that have already resulted or may result from these tests. For one, they argue that uncertainty is not really relieved by these tests because they do no indicate whether or not the person will develop the disease, and the time frame that the disease could occur. They also point out that the person who receives a positive test result may become obsessed with worrying. Nancy Wexler, a clinical psychologist from Columbia University, states that some people may "end up hospitalizedónot for the disease, but for depression. Even a negative test result can create problems, when a test suddenly removes the specter on which a whole life has been organized" (Time 1996).
Even doctors point out the problems of genetic testing. These tests may often produce false-positive or false-negative results. Negative results can give a person a false sense of security. Just because a person has a negative test result to a specific gene mutation doesnít mean that they will not develop cancer, or another disease from other environmental or genetic factors. For example, women without the BRCA1 mutation still have a 12% risk of developing breast cancer, which all women face. Opponents also argue that consumers donít understand the meanings of the test results. Many people are not aware that these tests only indicate the risk of developing a certain disease. Education and counseling are necessary, but there is currently a shortage of these specialists. Therefore, doctors not trained well in genetics are vulnerable to malpractice suits by giving out faulty information, no information, or not referring to a genetic specialist (Newsletter 1997).
Before I researched this topic, I had a general idea about genetic testing, but I did not realize exactly what issues people were discussing. I believe I have a much better understanding of the pertinent issues that are being debated about predictive genetic testing. After reading arguments from both sides, I have concluded that genetic tests do not provide a person with definitive results and therefore should not be used. I believe they do set up people with false hopes and possibly a false sense of security. In the articles I read to prepare for this paper, numerous examples were given of people belonging to high risk families who believe that genetic tests are not the answer.
Besides the reasons I stated given by opponents,family members also are concerned about discrimination from employers and insurers. I thought we are trying to end discrimination. Genetic testing only gives people more of a reason to categorize people into certain groups. Morally and ethically, I believe that genetic testing should not be performed if treatments are not available for that specific disease. What do we tell those people if they do test positive? "Well, sorry, we canít help you, but weíll let you know if a treatment becomes available." This seems rather shallow to me. And most predictive genetic tests cannot even definitely tell a person whether or not they will develop the disease. Genetic tests are here and available to consumers for a number of diseases, whether we like it or not. We cannot ignore their existence. The best thing we can do for consumers is to educate them about the pros and cons of predictive genetic testing and let them make the choice. Life is a series of choices and we need to embrace those choices. However, we must be able to live with the consequences of these choices.
Do you want to know if the news is bad? Time. Fall 1996. V148. N14. P29(1).
Genetic testing for cancer: itís here -whether we need it or not. HealthFacts. Feb 1996. V21. N201. P1(2).
Genetic testing: the controversial background check. Newsletter-Peopleís Medical Society. Feb 1997. V16. N1. P1(3).
Kahn, Patricia. Coming to Grips With Genes and Risk. Science. October 1996. V274. P496-498.
Understanding Gene Testing. U.S. Department of Health and Human Services. Obtained from: http://www.gene.com/ae/AE/AEPC/NIH/index.html.