Genomics, Cannabidiols Drive Epilepsy Research
Scientists recently converged in Philadelphia for the American Epilepsy Society’s (AES) 69th Annual Meeting, touting new studies and insights in the field of epilepsy. Researchers discussed new findings, including personalized medicine, and the promise of Cannabidiol in human and animal studies.
Epilepsy, a disorder in which nerve cell activity in the brain is disturbed, causing seizures, is the fourth most common neurological problem, following only migraine, stroke and Alzheimer’s. There is no cure for epilepsy, but there are a variety of treatment options. The disease is estimated to affect 2.2 million people in the U.S., with 150,000 people developing the condition each year.
Personalized medicine
Scientists at AES discussed how new technologies, such as gene editing using CRISPR-Cas9, and next-generation sequencing, are empowering them to take a new crack at the human genome and find new ways to diagnose and treat epilepsy.
“Recent advances in DNA sequencing and genomic technologies has facilitated a flood of discoveries in identifying genetic causes of epilepsy. Where we’ve been most successful is in the epileptic encephalopathies (EE),” lead author of one of the studies presented, Candace Myers, a senior at the University of Washington, said in a press conference.
EE’s are typically a pediatric epilepsy with an early onset, and are characterized by multiple refractory seizures with a generally poor prognosis. Ongoing epileptic activity also causes cognitive regression. This is one of the most severe forms of epilepsy and is not very common.
Myers’ work focused on gene discovery through targeted resequencing of candidate genes. “We’ve made significant advances in the last few years and we’ve come to appreciate two principals in identifying these genetic causes.”
The first is the genetic heterogeneity in epilepsy, which means, Myers said, that they have found at least 40 genes and each gene explains only a small fraction of cases. The researchers have also come to appreciate the role of de novo mutations. Myers explained that de novo mutation is a genetic change observed in the child that is not seen in the parent.
The gene candidates for Myers’ study were identified from the first project of an epilepsy consortium known as Epi4K, which investigates the genetic causes of epilepsy. One of the groups’ first projects was focused on trio exome sequencing. Exome sequencing is a technology that allows researchers to look at all 20,000 genes in the human genome at the same time. It is considered a very unbiased approach to gene discovery. The consortium sequenced 264 families—a trio meaning an affected child was sequenced as well as two unaffected parents—and the de novo approach was used as a filtering strategy to look for genetic changes in the child that are not in the parent.
Out of 264 families, there were 329 de novo mutations in 305 genes, which is about 1.2 de novo mutations per person.
For Myers’ study, a team including researchers from the University of Washington, the University of Melbourne, and the University of Southern Denmark took a subset of those genes, 27, and ranked them on specific criteria. The team made a gene panel and then sequenced a different cohort of 537 patients with the EE type of pediatric epilepsy.
“Results of the new study is that seven out of 27 of the genes yielded additional mutations. Of these seven genes it explains 3.2 percent of our cohort,” Myers said. “So for 17 patients out of 537, we were able to identify a molecular cause for the epilepsy.”
It is the first evidence that one of the genes, SLC1A2, can cause epilepsy in humans. There is a mouse model for that gene, Myers said. She also pointed out that 41 percent of the 17 mutations are recurrent. A recurrent mutation is a mutation that has been reported as pathogenic in an unrelated individual.
“We’ve confirmed roles for at least seven genes in the underlying causes of epilepsy and shown that these genes may contribute to a spectrum of conditions beyond Infantile Spasms or Lennox-Casaut syndrome, in which they were first discovered,” Myers said in a press release.
In a second study, researchers from the University of California San Francisco used CRISPR-Cas9 gene editing to expose how changes in the STXBP1 gene affect development in zebrafish. Mutations in the syntaxin-binding protein 1, STXBP1 have been linked to childhood epilepsy and other neurodevelopmental problems.
The stxbp1a gene in zebrafish is highly similar to human STXBP1, and scientists inactivated it in zebrafish models. Using zebrafish in epilepsy research has many advantages both on the genetic side and due to the potential for developing new therapies, Brian Grone, a postdoctoral researcher at UCSF involved in the study said at the press conference.
In their work, researchers observed that zebrafish with two copies of the mutated gene exhibited major deficits in motor control, developmental delay, excess pigmentation and early death. Zebrafish with one copy of the gene had more subtle defects, including a reduced escape reflex in response to threatening stimuli.
“Our study shows that severe movement impairments result when we disrupt a zebrafish version of STXBP1,” Grone said. “Findings such as these could drive the development of precision therapies for genetic forms of epilepsy.”
Cannabidiol for treatment-resistant epilepsy
Cannabidiol (CBD) is the most abundant non-psychoactive cannabinoid in the cannabis plant. There have been many animal studies in different species that show it has anticonvulsant effects, and there has been anecdotal evidence that it is also effective in children with treatment-resistant epilepsies such as Dravet Syndrome (DS) and Lennox-Gastaut Syndrome (LGS). Two studies at AES detailed the efficacy of Epidiolex, a pharmaceutical liquid formulation of the cannabidiol in humans.
The Food and Drug Administration (FDA) recently completed a double-blind randomized controlled Phase 3 trial of Epidiolex, and the analysis is expected to be done in February 2016.
Orrin Devinksy, director of the NYU Epilepsy Center presented the most updated data of Epidiolex from the Expanded Access programs, which is an open-label trial that took place at 16 sites. Open label means that all participants and physicians knew they were receiving and administering the drug and at what doses. No patients received placebos.
The data represents safety data for 313 patients, of which 261 patients had three months of continuous exposure to the drug. Participants in the study ranged in age from four months to 41 years, with a median age of 11.8 years. Devinksy explained that the cohort was made up of children and young adults with not only very treatment-resistant epilepsy, but very frequent seizures. Before the patients received Epidiolex, the median number of convulsive seizures over 28 days was 31, but the mean was 138.9.
Of the participants, 19 percent had no definite known cause of the epilepsy, DS was present in 17 percent, and LGS in 15 percent.
After 12 weeks, overall participants saw a 45 percent reduction in convulsive seizure frequency, and among all patients almost half (47 percent) experienced a 50 percent or greater reduction in seizures. Nine percent of all patients were seizure free and 13 percent with DS were seizure free. According to Devinksy, GLS patients also saw a very favorable response for atonic seizures, which is one of the most common types in that syndrome, with a median reduction of 71 percent.
“It’s important to highlight this is an extremely treatment refractory group,” Devinksy said at the press conference. “So these are numbers that are much greater than I would have predicted and certainly would have ever predicted from anything like a placebo response, although the randomized double blind studies will give us that more scientific data.”
Of side effects that were seen in 10 percent or more of patients, the most common included somnolence, diarrhea, fatigue, decreased appetite, convulsion and vomiting. Devinsky said that four percent of all patients quit the study because of side effects, and 12 percent withdrew due to lack of effectiveness. He noted that both those numbers are relatively low for an antiepileptic drug trial.
Michael Oldham, formerly at UCSF and currently at the University of Louisville, authored a related study that tested the long-term efficacy of Epidiolex. Researchers followed a subset of 25 patients at UCSF Benioff Children’s Hospital in San Francisco for one year. Participants had an average age of 9 and took cannabidiol in conjunction with their other anti-epileptic medication. At the press conference, Oldham said 36 percent of the participants saw a greater than 50 percent reduction in seizures and one participant with DS remained seizure-free after one year. Twelve people left the study for lack of effectiveness and one experienced a clear increase in seizure frequency from the CBD.
“This is a significantly drug-resistant population, so the fact that we did find from a third to 45 percent of patients with a greater than 50 percent reduction is quite remarkable, and definitely merits continuing to move ahead and certainly supports doing the randomized trial to see if that plays out,” Oldham said.
“These kind of response rates in such a treatment-resistant group with very high frequency occurrence of their seizures, it was a very positive and promising finding,” Devinsky said at the press conference of the studies. “I think this adds more fuel to the fire that this drug is definitely likely to be effective for some people.”
