KAT6A-Mutant iPSC-Derived Cortical Neurons Display Precocious Maturation, Dysregulated Electrophysiology, and Altered Morphology.

KAT6A syndrome is a complex neurodevelopmental disorder caused by heterozygous pathogenic KAT6A variants inflicting variable degrees of developmental delay and intellectual disability via a mechanism that remains largely uncharacterized. To further our understanding, we differentiated KAT6A syndrome patient-derived induced pluripotent stem cells into neural progenitor cells and cortical neurons. KAT6A syndrome patient-derived cells exhibit an altered transcriptome, with many of the dysregulated genes associated with autism spectrum disorder. At an early stage of differentiation, KAT6A-mutant cortical neurons show many elevated neurodevelopment-specific genes, including key transcription factors. Detailed electrophysiological measurements uncover that KAT6A-mutant cortical neurons display a hyperexcitability phenotype at an early stage of differentiation, followed by hypoexcitability at a later stage, compared with control neurons. These electrophysiological alterations were accompanied by decreased sodium and potassium currents. Remarkably, early KAT6A-mutant neurons exhibit a markedly lower percentage of GABA-positive neurons and increased spontaneous calcium activity as compared with control neurons. Moreover, multiple morphometric alterations in early-stage KAT6A-mutant cortical neurons indicate premature maturation, including increased neurite outgrowth, arbor complexity and soma size. Consistently, KAT6A knockout SH-SY5Y cells exhibit impaired differentiation capability and dysregulated gene expression. These novel findings establish the deleterious impact of pathogenic KAT6A variants on cortical neuron differentiation and electrophysiological function.