4-PBA acts not only as a chemical chaperone but also as an HDAC inhibitor, and we and others have shown that other HDAC inhibitors, such as valproic acid (VPA), counteract neurological diseases, including spinal cord injury and hearing loss, in mouse models by promoting neuronal differentiation (Abematsu et al, 2010; Kusaczuk et al, 2015; Wakizono et al, 2021). This evidence concerns the gene HDAC9 and nervous system disorder.