Novel gene therapy strategy for refractory epilepsy

Epilepsy affects up to 1% of the global population, imposing a significant economic burden on
society. Approximately 30% of patients are refractory to treatment with currently available drugs,
and they are left with very few other options. Refractory epilepsy is mostly focal but primary
generalized epilepsy can also be resistant to pharmacotherapy. Although surgical resection of the
epileptogenic zone can result in seizure freedom, it is unsuitable for 90% of people with refractory
epilepsy.
Gene therapy is a promising candidate as a rational replacement for surgical treatment of
pharmaco- resistant focal epilepsy. However, current experimental gene therapies are based on
either the permanent modification of neuronal excitability using exogenous gene delivery or the
exogenous delivery of light or chemicals to achieve on-demand modulation of neuronal activity. The
main limitations of those strategies are due to the limited size of genes that can fit in a viral vector
and to the non-specificity of these treatments. Overcoming these limitations is fundamental for
developing rational approaches for epilepsy, but it can also be extended to other neurological and
psychiatric diseases where the ability to modifying the expression of any desired gene or genes in
the genome would represent a game-changing strategy.
We recently published a study ('In vivo CRISPRa decreases seizures and rescues cognitive deficits in
a rodent model of epilepsy', Brain 2020) within an international collaboration with the San Raffaele
Institute in Italy, where we pioneered the use of CRISPR to treat intractable epilepsy. In this
published work, we upregulated the expression of an endogenous voltage-gated potassium channel,
Kv1.1, encoded by Kcna1, using a modified CRISPR approach, CRISPR activation (CRISPRa). This
genetic tool is based on using a nuclease-defective Cas9 protein in combination with one or more
synthetic guide RNAs (sgRNAs) to recruit transcriptional enhancers or suppressors to their regulatory
sequences, allowing the manipulation of any endogenous genes in the genome. For the first time we
showed that by upregulating endogenous Kv1.1 expression in the brain we were able to decrease
neuronal excitability and suppress seizures in a mouse model of acquired focal epilepsy. The
potential of this approach is to be able to modulate gene expression regardless of the size of target
gene, thus it can be a game-changer in the treatment of many other neurological disorders.