Targeting heterozygous dominant negative variant of KCNA2 using Gapmer ASO for the treatment of drug-resistant epilepsy

A missense mutation c.1220C>G of <i>KCN2A</i> gene was recently identified in an infant with epilepsy. <i>KCNA2</i> encodes K_V1.2 subunits that form voltage-gated potassium channels (VGKC) via tetrameric assembly. The mutation results in amino acid change P407R at the highly conserved <i>PVP</i> motif. Functional characterization revealed that mutant K_V1.2_P407R subunits formed loss-of-function channels and suppressed both K_V1.2 and K_V1.1 channel activities. Hetero-tetrameric assembly of the K_V1.2_P407R subunits with other neuronal voltage-gated potassium channels of Shaker subfamily could lead to general deficit of repolarizing potassium current and potentially underlie the enhanced seizure susceptibility. Indeed, expression of human K_V1.2_P407R in early postnatal rat cortical neurons or genetically engineered hESC-derived neurons disclosed broadening of action potential duration and early afterdepolarization (EAD), associating with reduced potassium current. We hypothesize that Gapmer antisense oligonucleotides (ASOs) targeted to c.1220C>G mutation will selectively degrade the mutant mRNA while allowing the remaining wild-type (WT) subunits to form functional channels. As a proof of principle, delivery of Gapmer packaged in lipid nanoparticle into cortical neurons selectively suppressed K_V1.2_P407R over the WT protein expression, reversing the broadening of action potential duration, abrogating the EAD and leading to overall increase in potassium current.