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Almost 20 years following the completion of the Human Genome Project — a historic scientific achievement that resulted in generating the first sequence of the human genome — gene therapy is no longer a futuristic vision. It is the medicine of today, reshaping how we treat rare diseases.

To understand why gene therapy has the potential to revolutionize the treatment landscape for conditions caused by genetic variations — particularly for rare diseases — let’s take a closer look at genes and their role in both health and disease.

Research into gene therapies began more than 30 years ago. In the 2010s, the first gene therapies were approved for use in the US and the EU.1,2 And today, 27 cell and gene therapies are approved in the United States.3 Rapid advancements in the field continue, with more than 2,000 therapies in development worldwide.4

What is gene therapy, and what are the potential benefits?

Gene therapy is an innovative treatment approach that uses genetic material to treat disease. Gene therapies are designed to target the cause of genetic diseases. Most rare diseases — almost 80% — are caused by a variant in a single gene, making these rare diseases potential candidates for gene therapy.5

By adding, inactivating, or repairing genes, gene therapy offers individuals suffering from genetic diseases options for treatment. Additionally, because gene therapies only require a single, one-time dose, these treatments may reduce lifetime costs of healthcare and burden (or impact) of chronic conditions on individuals, their families, and caregivers.

What is a gene, and what does it do?

Most of our body’s genetic information is stored in 23 paired chromosomes inside the nucleus of our cells. Each chromosome is made up of DNA that stores information to determine our unique characteristics. Specific sections of DNA are called genes. Each person typically gets two copies of each gene, one from each of their biological parents. These genes control everything from hair color, to height, to many other traits. As far as we know, humans have between 20,000 and 25,000 genes.6

What is a genetic disease, and how does it occur?

Genes are the blueprints providing instructions on how to make proteins for the body. Proteins play an important role in how our body functions. Unfortunately, these blueprints are not always correct. A gene variant, also known as a gene mutation, is a small change to the DNA within our genes that can alter the instructions for how proteins are built and work. Some mutations can lead to a disorder or illness that may affect how a person breathes, walks, or digests food. Gene changes can be inherited (passed along from parents), can happen as we age, can be caused by environmental factors (chemicals and radiation), or can happen spontaneously without a clear cause before birth.  These genetic changes can happen to anyone but sometimes there can be rare changes that cause disease by altering how specific proteins function.

How does gene therapy work?

There are several modalities of gene therapy, and ASGCT’s, “What are the different approaches to gene therapy7 provides a detailed overview of the nuances and differences.

To fix errors or missing parts in our genes, gene therapy can work in several ways. Generally, the treatment can introduce a new, fully functional gene into the body to supplement a disease-causing gene. Gene therapy can also inactivate a gene causing disease or introduce a new or modified gene into the cell to treat the disease. Once delivered into the cell, the genetic material gives the cell instructions for how to produce a protein. These instructions lead to corrective changes to account for the cell producing too much, not enough, or incorrect essential proteins.

How does genetic material enter a cell?

Gene therapy approaches are predominantly focused on gene addition or gene transfer delivered through a viral vector in order to introduce genetic material into a cell. These viral vectors can be designed to target certain cells in the body to deliver functional genetic material to treat disease.

There are two ways a viral vector can deliver genetic material into the cell. With ex vivo treatment, a person’s own cells are removed from the body and are then treated or modified with a gene therapy and once modified, returned into the body. In vivo treatment delivers genetic material directly into the body, for example, through a one-time injection or infusion.

What is the future of gene therapy?

After decades of progress, the future of gene therapy is incredibly promising. A flurry of recent successes has led to the approval of several transformative treatments for patients — with a strong pipeline poised to continue delivering on this innovation. With a growing number of rare diseases that can now be effectively addressed with these one-time therapies, the focus now is scaling these technologies to address thousands of rare diseases that exist and expanding beyond rare diseases to bring the promise of genetic medicine to an even greater number of conditions. By investing in the future of gene therapy, we can transform medicine, alleviate disease burden, and ensure patients have the treatments they need.

To learn more about cell and gene therapy, visit ASGCT’s gene therapy patient education resources.8


  1. FDA news release. FDA approval brings first gene therapy to the United States. August 30, 2017.
  2. EMA press release. European Medicines Agency recommends first gene therapy for approval. July 20, 2012.
  3. Food and Drug Administration. Approved Cellular and Gene Therapy Products.
  4. World Economic Forum. Accelerating Global Access to Gene Therapies: Case Studies from Low-and Middle-Income Countries.,the%20forefront%20of%20modern%20medicine.
  5. National Institutes of Health, National Center for Advancing Translational Sciences.
  6. National Institutes of Health. National Human Genome Research Institute. Introduction to Genomics.
  7. American Society of Gene and Cell Therapy. What are the Different Gene Therapy Approaches?
  8. American Society of Gene and Cell Therapy. Gene Therapy 101.