New disease models for investigating SynGAP1-related disorder (SRD) caused by a common heterozygous nonsense SYNGAP1 mutation

Abstract

Mutations in the SYNGAP1 gene cause SynGAP1-related disorder (SRD), a severe neurodevelopmental disorder marked by intellectual disability, epilepsy, ataxia, autism spectrum disorder, and global developmental delay. Studies in mouse models of SRD show that restoration of SynGAP1 expression in adult animals improves memory and seizure threshold, highlighting the disorders potential for successful therapeutic intervention over the entire lifetime. We established an integrated disease-modelling pipeline centered on the recurrent SYNGAP1 c.427C>T, p.(Arg143Ter), nonsense mutation, integrating neuronal and organoid models from patient-derived human induced pluripotent stem cells (hiPSCs) and a humanized knock-in mouse line to investigate mutation-specific disease phenotype across complementary experimental systems. We demonstrate that the c.427C>T mutation leads to a reduction of SynGAP1 protein levels and a corresponding dysregulation of Ras/ERK signaling in human forebrain organoids as well as in the mouse model system. In vivo, mice harboring the c.427C>T mutation show a hyperactivity phenotype that corresponds well to phenotypic features seen in patients such as absence of fear, hyperactive behavior and a strong urge to investigate the immediate surroundings. Taken together, our molecular and behavioral data in the humanized mouse are in line with studies on conventional heterozygous SynGAP1 knockout models, underscoring the relevance of these new disease models for further investigations into disease pathology. Moreover, with the three models described here, we present a translational platform that enables the development and evaluation of gene therapies that target disease-causing single nucleotide variations in the SYNGAP1 coding sequence.