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Gene therapy has been studied for more than 40 years and can help stop or slow the effects of disease on the most basic level of the human body - our genes. And to understand how it works, we’ll start at the basics.

Understanding genes

Genes are made up of DNA, which are blueprints to build enzymes and proteins that make our body work. As far as we know, humans have between 20,000 and 25,000 genes. We typically get two copies of each gene from our parents. They influence everything from the color of our hair to our immune system, but genes aren’t always built correctly. A small adjustment to them can change how our proteins work, which then alters the way we breathe, walk or even digest food. Genes can change as they go through inherited mutations, as they age, or by being altered or damaged by chemicals and radiation.

How gene therapy can help

In cases when a gene changes – also known as mutating – in a way that causes disease, gene therapy may be able to help. Gene therapy is the introduction, removal or change in genetic material – specifically DNA or RNA – into the cells of a patient to treat a specific disease. The transferred genetic material changes how a protein or group of proteins is produced by the cell.

This new genetic material or working gene is delivered into the cell by using a vector. Typically, viruses are used as vectors because they have evolved to be very good at sneaking into and infecting cells. But in this case, their motive is to insert the new genes into the cell. Some types of viruses being used are typically not known to cause disease and at other times the viral genes known to cause disease are removed. Regardless of the type, all viral vectors are tested many times for safety prior to being used. The vector can either be delivered outside the body (ex-vivo treatment) or the vectors can be injected into the body (in-vivo treatment).

Other types of drugs are typically used to manage disease or infection symptoms and to relieve pain, while gene therapy targets the cause of the disease. It is not provided in the form of a pill, inhalation or surgery, it is provided through an injection or IV. 

Gene therapy can help with adding to or changing non-functioning genes – creating a great opportunity to assist with rare inherited disorders, which are passed along from parents. The mutation might be present on one or both chromosomes passed to the children.

What counts as a rare disease?

Gene therapy treats diseases in patients that are rare and often life-threatening. The European Union considers a disease as rare when it affects less than 1 in 2,000 citizens.

As of now, there are around 6,000 clinically defined rare diseases, affecting between 3% and 6% of the worldwide population. Currently, 72% of these rare diseases are caused by a simple genetic mutation inherited from one or both parents and, of those, 70% start in childhood.

Which diseases have gene therapies?

The majority of gene therapies are currently being studied in clinical trials and are focused on some of these inherited diseases include (but are not limited to):
- Haematology/blood disorders like sickle cell disease
- Neurological disorders that affect the brain and spinal cord
- Musculoskeletal diseases
- Retinal disorders
- Oncology (blood cancers)

Why do we use viral vectors?

As you know from the cold and flu season and especially from the COVID-19 pandemic, viruses are skilled in the art of invading our bodies, adding their genetic material into our cells. Researchers have learned to harness this ability to our advantage. Viruses are often used as a vehicle to deliver “good” genes into our cells, as opposed to the ones that cause disease.

Viruses are sometimes modified into vectors as researchers remove disease-causing material and add the correct genetic material. In gene therapy, researchers often use adeno-associated viruses (AAV) as vectors. AAV is a small virus that isn’t typically known to cause disease in the first place, therefore significantly reducing a chance of a negative reaction.
Last updated: 27 May 2021
This content was adapted from the American Society of Gene and Cell Therapy Patient Information Program 
The American Society of Gene and Cell Therapy is the creator of the video content on this page

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