Zourray, Clara; (2024) A 3D Human Cortical Assembloid Model of Dravet Syndrome Reveals a Novel Role for SCN1A in Early Human Corticogenesis. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Dravet Syndrome (DS) is a severe neurodevelopmental disorder associated with epilepsy as well as motor, behavioural and cognitive impairments. Seizures in DS are usually refractory to anti-epileptic drugs and there is currently no cure for this disease. DS is in most cases caused by heterozygous loss-of-function mutations in SCN1A, resulting in haploinsufficiency of the Nav1.1 voltage-gated sodium channel. Genetic therapies aimed at restoring Nav1.1 function are currently in clinical trial and could represent disease-modifying treatments for patients. However, important physiological and genetic differences between mice and humans require the development of a novel human disease model to further our understanding of disease pathophysiology and ensure efficient clinical translation. To address this, we aimed to develop a 3D human cortical assembloid model using patient-derived iPSCs. We first showed that this model successfully recapitulates the tangential migration of human cortical interneurons, as well as their functional integration within cortical networks. We demonstrated successful induction of epileptiform activity in this model and used it as a platform to test novel gene therapies for epilepsy. Then, we successfully generated three DS patient iPSC lines, two of which were corrected using CRISPR-Cas to obtain isogenic controls. Differentiation of the patient and control lines revealed an unexpected phenotype affecting the G2/M cell cycle transition in cortical progenitors at early developmental stages and resulting in premature generation of excitatory cortical neurons. These defects were found to be caused by an early transient prenatal expression of Nav1.1, with a different physiological role. These results reveal a novel role for Nav1.1 in early corticogenesis, improving our understanding of disease pathogenesis and opening new avenues for the study of sodium channels in human cortical development. Moreover, at later stages of development, our DS model shows a clear epileptiform phenotype, making it a suitable platform for preclinical testing of novel gene therapies.

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