Presynaptic dysfunction in CASK-related neurodevelopmental disorders

CASK-related disorders are a growing group of genetic neurodevelopmental syndromes. There is limited information about the effects of CASK mutations in human neurons. Therefore, we sought to delineate CASK mutation consequences and neuronal level effects using induced pluripotent stem cell-derived neurons from two mutation carriers; one male diagnosed with ASD and a female with MICPCH. We show a reduction of the CASK protein in maturing neurons from the mutation carriers, which leads to significant downregulation of gene sets involved in presynaptic development and CASK protein interactors. Furthermore, CASK-deficient neurons showed decreased inhibitory presynapse size as indicated by VGAT stainings, which may alter E/I balance in developing neural circuitries. Using in vivo magnetic resonance spectroscopy quantification of GABA in the male mutation carrier, we further highlight the possibility to validate in vitro cellular data in brain. Our data shows that future pharmacological and clinical studies on targeting presynapses and E/I imbalance could lead to specific treatments for CASK-related disorders.

CASK相关障碍是一类日益受到关注的遗传性神经发育综合征群。目前关于CASK突变对人类神经元的影响的研究数据仍较为匮乏。为此，本研究选取两名CASK突变携带者的诱导多能干细胞分化神经元，旨在阐明CASK突变的致病效应及其在神经元层面的作用机制；两名携带者分别为一名确诊为孤独症谱系障碍（Autism Spectrum Disorder, ASD）的男性患者，以及一名患有MICPCH的女性患者。研究发现，突变携带者的成熟神经元中CASK蛋白表达量显著降低，这导致突触前发育相关基因集及CASK蛋白互作因子编码基因的表达显著下调。此外，通过囊泡γ-氨基丁酸转运体（Vesicular GABA Transporter, VGAT）染色结果显示，CASK缺陷神经元的抑制性突触前结构尺寸减小，这可能会改变发育中神经环路的兴奋-抑制（Excitation/Inhibition, E/I）平衡。通过对该男性突变携带者体内的γ-氨基丁酸（γ-Aminobutyric Acid, GABA）进行磁共振波谱（Magnetic Resonance Spectroscopy, MRS）定量分析，本研究进一步证实了可在活体大脑中验证体外细胞实验数据的可行性。本研究数据表明，未来针对突触前结构及兴奋-抑制失衡的药理学与临床研究，有望为CASK相关障碍开发出针对性治疗方案。