KCNQ variants and pain modulation: a missense variant in Kv7.3 contributes to pain resilience Jun-Hui Yuan, 1,2,3, * Mark Estacion, 1,2,3, * Malgorzata A. Mis, 1,2,3, * Brian S. Tanaka, 1,2,3, * Betsy R. Schulman, 1,2,3 Lubin Chen, 1,2,3 Shujun Liu, 1,2,3 Fadia B. Dib-Hajj, 1,2,3 Sulayman D. Dib-Hajj 1,2,3 and Stephen G. Waxman 1,2,3 * These authors contributed equally to this work. There is a pressing need for understanding of factors that confer resilience to pain. Gain-of-function mutations in sodium channel Nav1.7 produce hyperexcitability of dorsal root ganglion neurons underlying inherited erythromelalgia, a human genetic model of neuropathic pain. While most individuals with erythromelalgia experience excruciating pain, occasional outliers report more moderate pain. These dif- ferences in pain profiles in blood-related erythromelalgia subjects carrying the same pain-causative Nav1.7 mutation and markedly different pain experience provide a unique opportunity to investigate potential genetic factors that contribute to inter-individual variability in pain. We studied a patient with inherited erythromelalgia and a Nav1.7 mutation (c.4345T>G, p. F1449V) with severe pain as is characteristic of most inherited erythromelalgia patients, and her mother who carries the same Nav1.7 mutation with a milder pain phenotype. Detailed six-week daily pain diaries of pain episodes confirmed their distinct pain profiles. Electrophysiological studies on subject-specific induced pluripotent stem cell-derived sensory neurons from each of these patients showed that the excitability of these cells paralleled their pain phenotype. Whole-exome sequencing identified a missense variant (c.2263C>T, p. D755N) in KCNQ3 (Kv7.3) in the pain resilient mother. Voltage-clamp recordings showed that co-expression of Kv7.2-wild type (WT)/Kv7.3-D755N channels produced larger M-currents than that of Kv7.2-WT/Kv7.3-WT. The difference in excitability of the patient-specific induced pluripotent stem cell-derived sensory neu- rons was mimicked by modulating M-current levels using the dynamic clamp and a model of the mutant Kv7.2-WT/Kv7.3-D755N chan- nels. These results show that a ‘pain-in-a-dish’ model can be used to explicate genetic contributors to pain, and confirm that KCNQ var- iants can confer pain resilience via an effect on peripheral sensory neurons. 1 Department of Neurology, Yale University School of Medicine, New Haven, CT 06520, USA 2 Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, CT 06520, USA 3 Center for Rehabilitation Research, VA Connecticut Healthcare System, West Haven, CT 06516, USA Correspondence to: Stephen G. Waxman, MD, PhD Neuroscience and Regeneration Research Center, VA Connecticut Healthcare System 950 Campbell Avenue, Building 34, West Haven, CT 06516, USA E-mail: stephen.waxman@yale.edu Keywords: Erythromelalgia; induced pluripotent stem cells; pain; potassium channel; whole-exome sequencing Abbreviations: AP ¼ action potential; BFNS ¼ benign familial neonatal seizures; DRG ¼ dorsal root ganglion; G– V ¼ conductance–voltage; HEK293 ¼ Human Embryonic Kidney Cells 293; IEM ¼ inherited erythromelalgia; iPSC ¼ induced pluri- potent stem cell; I–V ¼ current–voltage; MIMMendelian Inheritance in Man; NIS ¼ neuronal imaging saline; NRS ¼ numerical rat- ing scale; PBS-T ¼ phosphate buffered saline-tween; PFA ¼ paraformaldehyde; RMP ¼ resting membrane potential; SEM ¼ mean 6 standard error; WES ¼ whole-exome sequencing; WT ¼ wild type Received July 13, 2021. Revised July 13, 2021. Accepted July 29, 2021. Advance Access publication September 8, 2021 V C The Author(s) (2021). Published by Oxford University Press on behalf of the Guarantors of Brain. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. doi:10.1093/braincomms/fcab212 BRAIN COMMUNICATIONS 2021: Page 1 of 15 | 1 Downloaded from https://academic.oup.com/braincomms/article/3/3/fcab212/6366547 by guest on 05 July 2022