Dravet syndrome (DS) is a rare, genetic epileptic encephalopathy that gives rise to seizures that don’t respond well to seizure medications. It begins in the first year of life in a healthy infant or toddler and can include a spectrum of symptoms ranging from mild to severe.
The average life expectancy of youngsters with the syndrome is usually short, with 10% to 20% dying from sudden unexpected death in epilepsy (SUDEP) by the age of 10.
The syndrome is a severe form of epilepsy characterized by frequent, prolonged seizures (beginning before the age of 15 months) often triggered by high body temperature (hyperthermia), developmental delay, speech impairment, ataxia, hypotonia, sleep disturbances and other health problems. It’s caused by a genetic mutation in the SCN1A gene, which when normal is required for the proper function of brain cells.
The syndrome was named after French pediatric epileptologist and pediatric psychiatrist Charlotte Dravet – who is now an octogenarian. She had the opportunity, to accompany and observe inpatients for many years, which resulted in some of her major contributions to epileptology.
There is hope
But there is hope. Researchers at Tel Aviv University (TAU), among other institutions, have developed an innovative gene therapy in lab mice that could eventually help children suffering from DS, which results from a mutation and is not inherited from the parents but occurs randomly in the fetus. They published their findings in the Journal of Clinical Investigation under the title “Viral vector–mediated expression of NaV1.1, after seizure onset, reduces epilepsy in mice with Dravet syndrome.”
Children with DS initially show focal seizures confined to one area of the brain or generalized throughout the brain. These initial seizures are often prolonged and involve half of the body and may be followed by seizures that switch to the other side of the body. Other seizure types emerge after the age of one year and can be quite varied. Status epilepticus – a state of continuous seizure requiring emergency medical care – may occur frequently, particularly before age five.
As DS children typically have normal development in the first few years of life, after that, their seizures increase and the pace of acquiring skills slows, so sufferers begin to lag in development behind their peers. Other symptoms can begin throughout childhood with changes in eating, appetite, balance and a crouched gait.
Dr. Moran Rubinstein, who headed the team, said that “DS, whose incidence is approximately one in 16,000 births, is considered relatively common among rare genetic diseases. As of today, there are about 70 Israeli children who suffer from it… The disease is not characteristic of a certain segment of the population, cannot be predicted in advance or discovered during pregnancy.”
DS seizures are difficult to control but can be reduced by anticonvulsant drugs including oxcarbazepine, carbamazepine, phenytoin and lamotrigine – but these should not be used on a daily basis because they may make seizures worse. A ketogenic diet high in fats and low in carbohydrates also may be helpful. The US Food and Drug Administration (FDA) has approved fenfluramine and cannabidiol to treat seizures with DS in children after their second birthday.
Recently developed genetic therapies have been found to be effective in DS mice, and some of them are even now in the phase of clinical trials in humans. However, these treatments have demonstrated efficacy in DS mice only when given at very early stages, even before the onset of symptoms. Since gene therapy is a complex and invasive procedure, it will not be given to children without a clear diagnosis of DS.
“Therefore, in this study, they concentrated on developing a treatment that would be effective after the onset of seizures even at a relatively late age. In addition, since the syndrome also includes developmental delays, we sought to develop a treatment that would alleviate both the epilepsy and the cognitive symptoms,” Rubinstein said.
In genetic therapies, viruses are often used as carriers that transport normal genetic material into the patient’s body for it to be added to the damaged DNA and enable normal activity, Rubinstein continued. “For this purpose, the virus is engineered; its original genetic material is removed so it cannot cause disease or replicate itself, and instead, the relevant normal gene is packed inside. In the case of DS, since the SCN1A gene is very large, it wasn’t possible to use common viruses that are usually used for this purpose and a virus capable of carrying and transferring large genes was needed. In our study, we solved this problem by using a virus called Canine adenovirus type 2 as a carrier of the normal gene.”
Next, the researchers injected the carrier virus directly into the brains of DS mice in order for the virus to infect the malfunctioning nerve cells. The researchers explain that the treatment requires direct injection into the brain because the size and properties of the virus don’t allow it to pass through the blood-brain barrier.
Thirty-one mice were treated at three weeks of age, after the onset of spontaneous convulsions (equivalent to one to two years of age in children), and 13 mice were treated at five weeks of age (equivalent to six to eight years of age in children). The injection was performed in several areas of the brain, and in addition an empty virus was injected into the brains of 48 mice as controls.
The highest efficacy was seen when the treatment was injected at three weeks of age. In these mice, the seizures stopped completely within just 60 hours of injection, life expectancy increased significantly and the cognitive impairment was fully repaired. Even in mice treated at five weeks of age, a significant improvement was observed as a decrease in epileptic activity and protection from thermally-induced seizures.
For the mice in the control group mice that received an empty virus, no improvement was observed and they suffered from the symptoms of the disease just like untreated mice; about 50% of them died an early death as a result of the severe epilepsy. In addition, the treatment was applied to healthy mice with no harmful results, which was proof of its safety.
When a virus carrying a normal SCN1A gene was injected into the brains of DS mice, the treatment was found to be effective in a variety of critical aspects including improvement in epilepsy, protection from early death and significant improvement of cognitive abilities. Importantly, this treatment was effective after the onset of severe epilepsy from DS.
“Our treatment added a normal gene to the damaged neurons in the brain, which was enough to restore them to normal function. The return of the normal gene in its entirety is particularly important for treating DS because in different children, the mutation occurs in different places in the gene and injecting a complete gene is a uniform treatment suitable for all DS patients,” the TAU team said. “In addition, we found that the virus chosen for the purpose of the study infects many nerve cells in the brain, and spreads widely beyond the injection site, adding to its effectiveness.”
“We hope that the technique we developed in the laboratory will also reach the clinic in the future and help children with this serious disease,” the team said. “In addition, since there is a similarity between Dravet and other rare developmental epilepsies in terms of the patient’s symptoms and brain changes, we hope that this treatment can also help other types of genetic epilepsies, and we think that the tools we developed in this research will pave the way for the development of similar treatments for other rare diseases.”
The research was conducted under the leadership of Rubinstein and graduate student Saja Fadila, along with Anat Mavashov, Marina Brusel and Karen Anderson, all from Tel Aviv University’s Faculty of Medicine and the Sagol School of Neuroscience at Tel Aviv University, and Dr. Eric Kremer, from the University of Montpellier in France. Also participating in the study were Bertrand Beucher and Iria González-Dopeso Reyes from Montpellier and other researchers from France, the US and Spain.
The researchers added that “it is common nowadays to perform a genetic analysis for children who suffer from complex thermally-induced seizures around the age of six months. But even if the test detects that the problem is in the SCN1A gene, the final diagnosis is often given after epilepsy worsens, with the appearance of severe spontaneous convulsions and developmental delays. Although it is important to have an early diagnosis, this is often delayed, and most children are diagnosed only at the age of one or two years and sometimes even later.”
Rubinstein concluded that “the treatment we developed is the first that has been proven to be effective for DS when given after the onset of spontaneous convulsions, and the first that resulted in an improvement in the cognitive function of the DS mice. We registered a patent and hope that in the future, the treatment will reach the clinic and help children suffering from it. We are currently investigating whether it may also be suitable for other genetic neurodevelopmental diseases. The platform we developed is a plug and play platform for genetic therapies, and perhaps in the future, we will be able to pack into the carrier virus different types of normal genetic material to treat additional diseases.”