A deleterious Nav1.1 mutation selectively impairs telencephalic inhibitory neurons derived from Dravet Syndrome patients

Abstract

Dravet Syndrome is an intractable form of childhood epilepsy associated with deleterious mutations in SCN1A, the gene encoding neuronal sodium channel Nav1.1. Earlier studies using human induced pluripotent stem cells (iPSCs) have produced mixed results regarding the importance of Nav1.1 in human inhibitory versus excitatory neurons. We studied a Nav1.1 mutation (p.S1328P) identified in a pair of twins with Dravet Syndrome and generated iPSC-derived neurons from these patients. Characterization of the mutant channel revealed a decrease in current amplitude and hypersensitivity to steady-state inactivation. We then differentiated Dravet-Syndrome and control iPSCs into telencephalic excitatory neurons or medial ganglionic eminence (MGE)-like inhibitory neurons. Dravet inhibitory neurons showed deficits in sodium currents and action potential firing, which were rescued by a Nav1.1 transgene, whereas Dravet excitatory neurons were normal. Our study identifies biophysical impairments underlying a deleterious Nav1.1 mutation and supports the hypothesis that Dravet Syndrome arises from defective inhibitory neurons.DOI: http://dx.doi.org/10.7554/eLife.13073.001

Can mutation‐mediated effects occurring early in development cause long‐term seizure susceptibility in genetic generalized epilepsies?

“…These methods have been used to model neural microarchitecture changes that accompany epilepsy disease progression, such as impaired neurite outgrowth in iPS‐derived neurons from individuals with Ohtahara syndrome, a severe epileptic encephalopathy . Furthermore, iPS cell–derived GABA‐positive inhibitory neurons carrying a mutation in SCN1A have been shown to replicate disease pathology previously identified in animal models including a reduction in voltage‐dependent Na + currents in inhibitory neurons . Recently, neurodevelopmental and synaptic changes in a human stem cell–based model of tuberous sclerosis were rescued using pharmacological intervention .…”

A novel GABAergic dysfunction in human Dravet syndrome

“…The use of induced pluripotent stem cell (iPSC)-derived neurons from patients led to important results, even if with some discrepancies (i.e., an increase or deficit in the sodium current density), probably due to differences in neuronal differentiation protocols. 3,13 To overcome the limited availability of DS tissues, one approach to study GABAergic transmission in rare human epileptic diseases is the microtransplantation of GABA A Rs from human brain into Xenopus oocytes. 14 The advantage of this technique is the possibility of investigating human GABA A Rs using a minimal amount of autoptic brain tissue of DS patients, bypassing the transcriptional and translational machinery of the host cell.…”

Progress in the molecular mechanisms of genetic epilepsies using patient‐induced pluripotent stem cells

“…interneurons. 21,26,53 Moreover, until a later period of differentiation, the sodium ion currents, action potential thresholds, and spontaneous discharge frequencies in these 2 conditions were demonstrated to differ from those of healthy controls. The overactivation of sodium channels leads to enhanced neuronal activity, which leads to network hyperexcitability.…”

“…The sodium currents and action potentials in the glutamatergic neurons from the Dravet syndrome patients were stronger than those from the GEFS+ patients, which is consistent with the severity of the clinical seizures in the 2 conditions. However, several subsequent studies using iPSCs combined with CRISPR/Cas9 gene repair techniques, and neuron‐specific fluorescence labeling techniques confirmed that SCN1A gene mutations are more likely to cause reduced inhibition throughout the neural network by weakening the activity of interneurons . Moreover, until a later period of differentiation, the sodium ion currents, action potential thresholds, and spontaneous discharge frequencies in these 2 conditions were demonstrated to differ from those of healthy controls.…”