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Activity 6: Gene Therapy


Students will assess the risks and benefits of different gene therapies.

Background Information

Gene Therapy involves the insertion of new genetic material into cells in a patient's body. By inserting manipulated DNA directly into the body, doctors can correct or enhance a particular cellular function, such as enzyme production; increase the vulnerability of diseased cells; or, in some cases, block the operation of particular cells or cell functions.

Developing specific therapies requires several steps. First, researchers must determine the gene or genes that cause or affect the disorder. Next, they must decide on the best approach for solving the problem and determine how to modify DNA sequences to carry out that solution. And then researchers must find safe, efficient vehicles--called vectors--to carry the modified DNA to targeted cells. There are several vectors already in use, including chemical solutions, synthetic fat molecules, and viruses that have been modified so that they are harmless.

In each step of the process there is some degree of difficulty and risk. It is not always clear how modifying one gene may affect other genes in the DNA sequence, and if more than one gene needs to be modified, the chances of other genes being affected goes up. It is also possible that the integration of viral DNA into a cell's genome might accidentally activate genes that can trigger the growth of cancer. And it is difficult to target the correct cells to modify. For example, the cells responsible for producing mucous in cystic fibrosis patients are located in the patients' lungs. There is no easy way to remove and insert cells directly into the lungs, so current experimental procedures involve using a tube that drips a solution containing modified cells into the lungs. Doctors hope that enough cells will be reached by this process to effect a change.

In addition, there are many ethical issues involved in gene therapy. For example, some of the current questions being debated include: Which diseases should be targeted? How will the genetic manipulation be regulated? How much money should be spent on developing gene therapies for disorders for which alternative therapies already exist? Should genetic manipulation be used to eliminate defective genes from egg or sperm cells? Will genetic manipulation be used to "improve" the human species by selectively controlling for certain traits? Who should make these decisions?

A modified virus carrying the gene for the defective protein in people with cystic fibrosis enters a lung cell. The virus breaks down, and the modified DNA enters the nucleus of the cell. In the nucleus, transcription of the viral DNA produces single strands of messenger RNA, which migrate to the cytoplasm and begin producing a correct version of the defective protein.


For each pair of students:


Duplicate Gene Therapy Project Summaries and distribute to pairs of students.


  1. Divide the class into groups of four to six. Explain that each group represents a committee that oversees the development of new gene therapies. The committee decides which projects should be given money for research and development of a therapy. However, funds are limited, and only one new project can be funded.

  2. Ask the students to carefully read through the project summaries on the handout. Then ask each student to do a risk/benefit analysis for the projects to describe the issue and record information upon which to base his or her decisions. Explain that their risk/benefit analyses should contain the following five parts:

    • At least five facts about the proposed therapies
    • At least five opinions about the proposed therapies
    • At least five risks involved in developing the therapies
    • At least five benefits involved in developing the therapies
    • A decision statement that includes a rationale based on the risks and benefits involved.

    If necessary, you may want to help students get started by asking questions such as: How many people does the therapy affect? Are there specific ethnic groups that the therapy affects? Is the disorder fatal or debilitating? Does the therapy require modifying a single gene or more than one gene? Will modifying the genes cause unintended changes? Will the changes produced by the modified genes be inheritable? Are alternative treatments available for the disorder? If so, how effective are they?

  3. Once students have completed their risk/benefit analyses, have each group use the information to decide which project should be funded. Then have the groups present their decisions, along with their rationales, to the class. They should also indicate any additional information they might need to make a better decision.

Discussion Questions

  1. Which factors were most important to you in deciding which gene therapy project to fund? Which factors were least important? Why? Did all the members of your group agree on which project to fund? If not, what factors helped your group reach the final decision?

  2. Suppose there were a fourth project that involved developing a gene therapy to "change" skin color. Do you think such a project should be funded? Why or why not? What other information might you want to have about the project before you decide?

  3. Suppose it were possible to eliminate genes from egg or sperm cells that make us vulnerable to disease or aging. What are some of the consequences of changing the egg or sperm cells? Under what conditions do you think this practice should be allowed? Give reasons for your answers.


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