Electrophysiological signatures of a developmental delay in a stem cell model ofKCNQ2developmental and epileptic encephalopathy

Background KCNQ2 , encoding K V 7.2 ion channels, has emerged as one of the prominent genes causing early onset seizures with developmental delay ( KCNQ2 developmental and epileptic encephalopathy; KCNQ2 -DEE). KCNQ2 de novo loss-of-function (LOF) and associated neuronal hyperexcitability have been accepted as mechanisms contributing to seizures. To investigate the developmental impact of KCNQ2 LOF, we generated patient iPSC-derived models for two previously reported de novo variants, p.(Arg325Gly) and p.(Gly315Arg), linked to severe congenital DEE. Methods Functional investigation of the two variants was initially performed in Xenopus laevis oocyte system. Patient-derived iPSC lines were differentiated using NGN2- and embryoid body-based protocols yielding neurons roughly corresponding to mid- and mid-late gestational stages, respectively. K V 7- mediated M-current, passive neuronal properties, action potential generation and spontaneous oscillatory network activities were analysed with whole-cell patch clamping. Findings Studied KCNQ2 variants showed LOF with a dominant-negative effect in the heterologous system. Reduced M-currents in patient iPSC-derived neurons corroborated a LOF as the main pathomechanism. Interestingly, this led to the reduced neuronal firing of the early neurons and to a disruption of complex oscillatory activity, with significantly reduced duration and amplitude of these events in patient iPSC-derived neurons. Interpretation We provide experimental evidence for changing roles of the M-current throughout development and place disease variant-mediated M-current reduction in the context of the neuronal maturation in the prenatal brain. Based on the reduced neuronal firing and disrupted oscillatory activity seen in patient iPSC-derived neurons, we propose that a delayed/impaired maturation of neuronal and network properties underlies KCNQ -DEE caused by LOF variants.