Frequently Asked Questions


1. What is gene replacement therapy?

Gene replacement therapy, a type of gene therapy, is a potential way to treat genetic diseases. Gene replacement therapy addresses the root or underlying cause of a disease by replacing a missing or nonworking gene with a new, working copy of the gene.


2. How does gene replacement therapy work?

Gene replacement therapy aims to give the body a new, working copy of a missing or nonworking gene. The new gene sits inside the nucleus, or control center, of cells and allows the cells to produce the missing proteins that are critical for the body to function. Learn more


3. Is gene replacement therapy safe? Does it work?

All therapies are required to undergo testing in clinical studies to be approved by the Food and Drug Administration (FDA). All clinical studies, including those being conducted in gene replacement therapy, are monitored for safety and effectiveness of a treatment. The clinical study team works closely with the FDA to monitor potential risks both during and after its clinical studies.


4. Why are viruses used in gene replacement therapy?

Viruses are used in gene replacement therapy because of their natural ability to enter into the cells of the body. In gene replacement therapy, scientists alter or reengineer a virus so it can be used as a vector, or delivery vehicle, without causing disease in humans. The vector acts like an envelope in that it holds the new, working copy of the gene and delivers it to where it needs to go in the body. Once the new gene has been delivered to cells, the rest of the vector, including the viral shell (the delivery vehicle), is broken down and removed from the body. Learn more


5. Could gene replacement therapy help people with monogenic diseases?

A monogenic disease can be caused by one missing or nonworking gene or gene pair. Because gene replacement therapy delivers a new, working gene to the body, it has the potential to help people with monogenic diseases. Learn more


6. Can gene replacement therapy make you sick?

While certain viruses are used as vectors, the vehicles used to carry the new, working genes into the nucleus of the cell, scientists have changed them in ways that stop them from making you sick. Even though the disease-causing parts of the virus have been removed, as with all therapies, there can be risks, so be sure to talk to your doctor before starting a new therapy. Learn more


7. What are the main risks of gene replacement therapy?

Most of the risks of gene replacement therapy have to do with the viral vectors used to deliver the new gene into the cell. Long-term risks are not known. The general risks listed below may not apply to all gene-based therapies, but may include:

  • Unwanted immune system reaction. Your body’s immune system may see the newly introduced vector or working gene as an intruder and attack it. This may cause the new, working gene to never make it to the target cells or be lost once in the cells.
  • The wrong cells may be targeted. Because viruses often have an attraction for more than one type of cell, it’s possible that the viral vector may deliver the new, working gene to the wrong cells, causing cell damage or disease.
  • The new gene inserts in the wrong place. Some types of viral vectors insert themselves into our DNA. When the new, working gene is inserted in the wrong place, it may disrupt genes that are working correctly, causing disease such as cancer.
  • Unable to turn off the new working gene. Once the new gene has been delivered inside the nucleus it will begin to make the missing protein. Today, there is no way to “turn off” this new gene if the new gene or protein causes problems in the body.

8. What makes gene replacement therapy different from other gene-based therapies?

There are several different types of gene-based therapies. Gene replacement therapy addresses the root or underlying cause of a disease by replacing the function of a missing or nonworking gene with a new, working copy of the gene. Other types of gene-based therapies may insert, remove, change, or replace specific pieces of a person’s existing DNA or change how certain cells act. Learn more


9. How long does gene replacement therapy last?

Gene replacement therapy is a relatively new type of treatment. The first gene replacement therapy was approved by the FDA in late 2017. While clinical trials often last years and may demonstrate that a therapy is safe and effective during that time, it is difficult to know exactly how long gene replacement therapy will last for each and every person. The goal of gene replacement therapy is the long-term management of a genetic disease. However, because there are many other factors that may contribute to how long the benefits of a treatment last, this is an ongoing area of interest for scientists.


10. What is gene editing?

Gene editing enables scientists to add, remove, or replace part of person’s DNA at a specific spot along their DNA. At this time, there are no FDA-approved gene-editing therapies, and clinical trials have only recently started to investigate the effectiveness and safety in humans. There are many questions still to be answered, including the potential risk of editing the wrong segment of DNA, which could lead to the loss of working genes or increase the risk of developing certain types of cancer. Learn more


11. What is CAR-T cell therapy?

CAR-T stands for chimeric antigen receptor (CAR) T-cell therapy. It is a type of cell therapy that is used with gene therapy but it is not a type of gene therapy by itself. It involves changing a person’s own immune cells to recognize and fight cancer cells inside the body. At this time, the FDA has approved 2 CAR-T cell therapies, with others being investigated. Learn more