One of the fastest growing and most exciting new ideas in epilepsy research is ‘gene therapy’. It’s something that you’ll see mentioned time and time again on Epilepsy in English, but what does it mean?
The short definition is this: gene therapy is modifying the genetic makeup of a cell in a way that treats a disease. This can be by adding, deleting, or modifying existing genetic code.
In theory gene therapy could be targeted to a wide range of disease but, for the purposes of this blog, we will focus on epilepsy.
How does it work?
There are a few technical steps needed to achieve a successful gene therapy. First, we need some way to get our new genetic material into the brain cells that we want to treat. This is usually done with something called a viral vector. This is basically a harmless version of a disease-causing virus. What’s great about viruses is that we can package new genetic material inside them and then they are naturally very good at getting into cells and spreading this genetic information. What’s more, we can also include a genetic promoter – a tag which means that the new genetic code only appears in specific cell types of our choosing.
So, let’s think of this in terms of epilepsy. We know that it is a disease where brain cells are more active than normal. With gene therapy we can insert a piece of genetic code which is designed to make cells less active, and we can include a promoter which makes this specific to brain cells. There are loads of possible strategies to make cells less active and you can see an example in this blog post.
Why gene therapy?
In general there is a big need for new approaches towards epilepsy treatment. The conventional wisdom is that in about one third of patients, their seizures are not well-controlled by existing anti-epileptic drugs.
A huge advantage of gene therapy is that, if successful, it should only require one treatment. This is because the changes to the genetic code are permanent so, in theory, the anti-seizure effects should last forever. In reality though, the brain is a very dynamic organ and it is impossible to guarantee that it won’t adapt in some way to the genetic changes.
Another big appeal of gene therapy is the ability to target specific types of cells in the brain. This means that treatments can be targeted only to those cells which are involved in generating seizures. On the other hand, anti-epileptic drugs typically change the activity of all electrical cells in the brain – even those which are still working normally. This can lead to unwanted side effects.
Current limitations of gene therapy
A big drawback of gene therapy is that, at least at the moment, it needs to be injected directly into the brain. Admittedly this does sound like a scary prospect but surgery is already a treatment option for epilepsy. In fact, the surgery for gene therapy would probably be less invasive than current surgical treatments where small pieces of tissue have to be removed completely. Further, scientists are working on better ways to deliver the treatment. For example, in the future it might be possible to give gene therapies using a normal injection.
A second limitation of gene therapy is that it is currently only possible to treat a small region of brain cells, close to the injection of the treatment. This is ideal for epilepsies where the seizures always start in the same part of the brain – you can simply inject the gene therapy into that area and it should stop any seizures from beginning. The problem is that in some cases, seizures can start from different places. At the moment it would be very difficult to apply a therapy to the entire brain, but again this may become possible as the field develops.
Finally, gene therapies for epilepsy have only been tested in rodents so far. The results of these studies are promising but there are still steps to overcome before they make it to the clinic. In 2018, Stephanie Schorge and Dimitri Kullmann (University College London) received funding to begin clinical trials for one of the most promising gene therapies in epilepsy. Patients who are scheduled for epilepsy surgery at the neighbouring National Hospital for Neurology and Neurosurgery will be able to opt in to receive a gene therapy treatment prior to their surgery. This provides the fail-safe that the treated tissue can still be removed, as previously planned, in the unlikely event of unwanted side effects. Taking a more optimistic view, the hope is that the successful gene therapy treatment will mean that the trial patients no longer need the surgery at all.
Indeed, Prof Schorge told us: ‘The planned first-in-human trial feels like an enormous step for us. For years I’ve been telling funders, friends and family that it will be 5-10 years before our work could help any people with epilepsy. When I met with school children recently – I realised I had to change my slide, because it is possible our gene therapy could help patients by the end of this year’
Should gene treatment prove to be successful in initial patient trials, we could well be seeing epilepsy gene therapies in the clinic sooner rather than later.
- Gene therapy is modifying the genetic code of cells to change them in a way that treats disease
- New genetic code can be put into cells using viruses that have been made harmless
- If it works, gene therapy can be a one-off permanent treatment with few side effects
- Clinical trials are beginning for the most promising gene therapies in epilepsy