Dravet syndrome is a rare and severe form of epilepsy that appears in early infancy. It is characterized by frequent, lengthy, and treatment-resistant seizures that can be triggered by warm weather, fevers, or light.
Affected children often develop physical or cognitive impairments. In rare cases, symptoms may improve after age six.
Most cases of Dravet syndrome are caused by mutations in a gene called SCN1A. This gene encodes for a protein that forms the sodium channels on the surface of nerve cells.
Sodium channels are an important part of the correct functioning of the brain and nervous system. When the sodium channels are defective, the activity of the nervous system is impaired and this is what is thought to cause the seizures in Dravet syndrome.
There is currently no cure for the condition but the seizures can be controlled with a ketogenic diet and through epilepsy medications, although these treatments are not always effective. Gene therapy is a new approach that is being developed as a potential treatment for Dravet syndrome.
What is gene therapy?
Gene therapy is a novel approach that uses a vector, such as a virus, to introduce a new version of a gene into a patient’s body. Gene therapy can:
- prevent the mutated gene in the patient’s body from producing the disease-causing protein;
- replace the mutated gene with a functional gene;
- increase the production of a functional protein from a gene that is already in the patient’s body;
- target other genes responsible for helping a certain protein to fold properly.
Gene therapy is used in laboratory animals for research, or to create genetically modified crops or cells that are able to produce molecules or enzymes for medications. Its use in humans as a potential therapy is still in early phases of development.
Key challenges of gene therapy include finding vectors that can transport the desired gene efficiently to the cells and ensuring that the therapeutic gene is placed in the correct part of the genome.
Gene therapy for Dravet syndrome
Dravet syndrome and other epilepsy disorders that are caused by mutations in the SCN1A gene pose challenges for gene therapy. The SCN1A gene is too big for many vectors, so gene replacement therapy is, for the moment, not possible. And because Dravet syndrome is caused by a deficiency in the correct protein, gene suppression alone is not a viable approach either.
Individuals with Dravet syndrome typically have a second healthy copy of the SCN1A gene, so the most promising avenue for gene therapy seems to be a combination of two approaches: increasing the production of the healthy gene and suppressing the mutated gene. It is not yet known how this can be done.
Current research
Research on gene therapy in Dravet syndrome specifically and on SCN1A, in general, is in the very early stage of development.
A study to explore gene therapy for Dravet syndrome headed by Simon Waddington and Rajvinder Karda at University College London’s Gene Transfer Technology Group was funded through a medical research grant in August 2017.
The project’s goal is to develop modified virus vectors that will be able to deliver a healthy copy of the SCN1A gene to affected neurons in mouse models of Dravet syndrome. This project is currently in progress.
The gene transfer group previously demonstrated effective gene therapy for epilepsy in rats. Positive results from this study were published November 2012 in the scientific journal Science Translational Medicine.
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