Hypokalemic periodic paralysis (HypoPP) is a dominantly inherited disorder of skeletal muscle in which recurrent attacks of weakness are caused by intermittent failure of fiber excitability. Episodes occur in association with hypokalemia (K+ < 3 mM) and are often triggered by carbohydrate ingestion, exercise, or stress. The molecular defect in HypoPP is heterogeneous, with 60% of families having missense mutations in CACNA1S encoding the L-type Ca channel CaV1.1, and 20% have missense mutations in SCN4A encoding the voltage-gated Na+ channel NaV1.4. Management of symptoms is limited to avoiding trigger factors, optimizing serum K+ levels, or empirical use of carbonic anhydrase inhibitors that have modest response rates (~50%) and adverse side effects. An even greater concern, with no existing therapeutic intervention, is the slowly progressive permanent muscle weakness (PMW) that impairs mobility and may cause loss of ambulation. All 14 HypoPP mutations in NaV1.4 and 10 of 11 in CaV1.1 occur at arginine residues in S4 transmembrane segments of voltage-sensor domains (VSD). We have been the leading group to show this consistent motif gives rise to a shared functional defect in HypoPP mutant channels: the anomalous gating pore leakage current. Moreover, simulations with our computational model show that this small anomalous conductance in CaV1.1 or in NaV1.4 (about 1% of the total resting fiber conductance) is sufficient to cause paradoxical depolarization of and associated inactivation of sodium channels, with subsequent loss of fiber excitability and weakness. Based on these insights on the pathogenesis of episodic HypoPP, we now propose new pharmacological and gene editing approaches for improved clinical management of HypoPP that will be tested and optimized in our knockin mutant CaV1.1-R528H mouse model of HypoPP. In Aim 1, our pharmacological approaches are directed at two separate targets: (i) block the gating pore and (ii) stabilizing by activation of KV7 K+ channels. Preliminary data show that HIFs (developed by our collaborator, F. Tombola, to block Hv1 voltage-gated proton channels) attenuate the low-K+ induced loss of force for CaV1.1-R528H muscle and block an inward current, consistent with block of the HypoPP gating pore leak. Other data show that retigabine, a KV7 opener, can prevent the low-K+ induced loss of force and hasten the recovery from weakness in R528H muscle. In Aim 2, two gene editing technologies will be used to develop a more durable improvement in symptom management that also has the potential to attenuate or prevent the late-onset PMW. The first approach is disruption of the mutant allele with CRISPR/Cas9. The rationale is that HypoPP is a dominant trait caused by a gain-of-function defect (gating pore current) and that one normal CACNA1S allele appears to be sufficient for normal muscle function in mice and humans. Our preliminary data show allele-specific disruption of R528H in vivo, with complete suppression of the...