What Is Gene Therapy & How Is It Used To Treat Diseases?

Cells are the basic units of a human body and Genes are the basic physical and functional units of heredity. Genes consist of instructions to build proteins that allow body cells to function properly. Approximately, there are about 20,000 genes in each human body cell.

However, genes get defective sometimes due to several reasons such as mutations, chromosomal abnormalities and single-gene disorders. While some gene disorders develop symptoms at birth, others show up over time. For instance, a heart defect is a genetic defect at birth. On the other hand, cancers, Alzheimer’s, and Schizophrenia are examples of genetic disorders that can appear later in life.

This article discusses ‘Gene Therapy’ that modifies defective genes to treat genetic disorders.

What Is Gene Therapy?

Gene therapy is a medical technique that modifies a person’s genes to treat or cure the patient’s genetic disorder.[1] Since gene therapy is challenging for both the patient and the medical professionals, it is considered only when other therapies become ineffective.

Gene therapy is used to treat inherited disorders such as cystic fibrosis, hemophilia, and sickle cell disease. Furthermore, the therapy is also effective in the treatment of cancer, infections, and HIV. Depending on the type of cell being treated, there are two types of gene therapies:

Somatic gene therapy: The gene is transferred to any bodily cell that does not make sperm or eggs. In somatic gene therapy, the side effects are not passed down to the patient’s children.
Germline gene therapy: The gene is transferred to specific cells that make sperm or eggs. In germline gene therapy, the side effects will be passed down to the patient’s children.

How Does Gene Therapy Work?

There are two reasons[2] why gene disorders happen:

Inherited Mutation: The whole or part of the gene can be defective or missing by birth. This condition is also referred to as genetically inherited mutation.
Acquired Mutation: Sometimes, healthy genes mutate due to environmental exposures over time, causing genetic disorders. While most such mutations are harmless, some inherited and acquired mutations can cause cancer, developmental disorders, and neurological diseases.

Based on the cause of the disease, medical specialists choose one of the three solutions in gene therapy:

Replacing a defective or missing gene with a healthy copy of the gene.
Adding a new or modified gene into the body to help treat the disease.
Inactivating a defective gene that is not functioning properly.

Gene Therapy: The Process

To add new genes directly into the cells, scientists use vectors. Vectors are genetically trained to deliver the necessary genes into the cells. However, vectors need to be efficient while delivering the genes into cells since they also carry certain risks.

There are four[3] major types of vectors used for gene therapy — plasmids, viral vectors, cosmids, and artificial chromosomes. Currently, viral vectors or viruses are the most used vectors in gene therapies because of their natural ability to deliver genetic material into cells. However, since viruses are prone to cause infectious diseases, they are modified before being used in gene therapies.

Source: https://www.fda.gov/

Gene therapy can be used to modify cells inside or outside the body. In this process, the vector carrying the gene gets injected directly into the patient in-vivo.

When cells are modified outside the body it is ex-vivo. In this process, the patient’s blood, bone marrow, or other tissue is needed to separate specific cell types in a lab and modify the gene. Later, the vector carrying the new gene is injected into the cells.

Challenges with Gene Therapy Treatment

Gene therapy is a new technique and it has several challenges[4] and risks. Below are some of the challenges:

1. Gene delivery to the appropriate cell

The new or modified gene must be injected into the specific cell. If not, the gene would cause health hazards in the wrong cell.

2. Turning on the gene

Another major challenge is turning the gene on after it’s injected into the cell. It’s because sometimes, new genes added through gene therapy are considered potentially hazardous intruders by the body’s immune system. And the immune system will try to damage the new gene. To prevent this, scientists use vectors that are less likely to provoke an immunological response.

3. Gene interferences

In gene therapy treatment, the new gene is expected to integrate into the patients’ genetic material and function appropriately thereafter. However, chances are that the new gene will interfere with the existing genes, halting its functioning or proving hazardous to the patient’s health. For example, if the new gene interferes with a vital gene involved in cell division regulation, it could lead to cancer.

4. Approach for therapeutic specificity

Each disease with a specific gene variation requires a specific approach[5] for gene therapy. For instance, people may have mutations in different genes but still have the same disease. In such a situation, each patient would likely need a specific gene therapy approach targeted at their specific gene variation. In other words, it leads to personalized medicine or treatment.

5. Tiny patients pool with rare diseases

Gene therapy is often used to treat rare diseases. Since most people have unique gene variations, it will take a long time gathering enough clinical data for potential treatments or even finding participants for such clinical trials. Therefore, rare genetic disorders make it even more challenging for scientists to develop potential treatments and hence it becomes extremely expensive and unaffordable.

Conclusion

Gene therapy treatment option has progressed significantly over the past few years. Clinical trials of gene therapy have also shown success in treating certain genetic disorders. However, the practical success is yet to be demonstrated for a wider population. However, many geneticists believe that gene therapy will be critically helpful in the future for curing rare inherited and genetic diseases.