Case Report: Targeted treatment by fluoxetine/norfluoxetine of a variant causing developmental and epileptic encephalopathy.

The Kv3.2 subfamily of voltage activated potassium channels encoded by the gene is abundantly expressed in neurons that fire trains of fast action potentials that are a major source of cortical inhibition. Gain-of-function (GOF) pathogenic variants in and , encoding Kv3.1 and Kv3.2 respectively, cause several types of epilepsy including developmental and epileptic encephalopathy (DEE). Fluoxetine (Prozac) is a known inhibitor of the Kv3.1 current and was reported to improve seizure control in a single patient with a GOF variant. Here, we describe fluoxetine treatment of two siblings with a V473A variant associated with DEE, which resulted in improved seizure control, ability to wean antiepileptic medications, and improved development. The V437A variant showed GOF activity as demonstrated by HEK293 cells expressing variant subunits activating at more hyperpolarized potentials than WT channels. Fluoxetine reduced currents equally for both Kv3.2 WT and Kv3.2-V473A variant channels, with an IC of ∼12 µM. Further analysis of this repurposed drug showed that norfluoxetine, a long-lasting metabolite of fluoxetine which is produced in the liver and accumulates in the brain, was more effective than fluoxetine itself in selectively inhibiting the dominant pathogenic channel activity of the pathogenic allele. Norfluoxetine showed 7-fold greater selectivity in inhibiting Kv3.2 variant currents (IC of ∼0.4 µM) compared to WT currents (IC of ∼2.9 µM). Combined with a previous report of improved outcomes for a variant, our results suggest that fluoxetine or its metabolite, norfluoxetine, may be beneficial for patients with GOF variants in and other neuronal potassium channels.