Abstract
Biallelic loss-of-function variants of Seizure Threshold 2 (SZT2) cause neurodevelopmental diseases with developmental delay, epilepsy, and macrocephaly. SZT2 forms the KICSTOR complex, which represses the mechanistic target of rapamycin complex 1 (mTORC1) amino acid-sensitive pathway. SZT2 dysfunction is thought to cause abnormal activation of the mTOR pathway, underlying the pathogenesis of SZT2-related diseases. We previously reported constitutive activation of mTORC1 in lymphoblastoid cell lines derived from patients with SZT2-related disease. However, the impact of SZT2 dysfunction on human brain development remains unclear. In this study, we examined the effects of SZT2 dysfunction on brain development using human brain organoids. We generated pluripotent stem cell-derived brain organoids and found a significantly greater number of outer radial glial cells (oRGCs) in the subventricular zone-like layer (SVZ) of SZT2 mutant (MT) brain organoids compared to control (WT) brain organoids. The number of upper-layer neurons, which generally originate from oRGCs, was also significantly greater in SZT2 MT brain organoids. Mechanistically, SZT2 MT brain organoids showed higher mTORC1 activity in the SVZ, where neural stem/progenitor cells amplify for cortical expansion in response to mTORC1 activity. Our data suggest that SZT2 dysfunction may cause macrocephaly through dysregulation of mTORC1 in early neural development.
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Data availability
The datasets supporting the findings of this study are available from the corresponding author upon request. The datasets of DNA sequencing from the SZT2 MT iPSCs are available in DDBJ repository (an INSDC member) under the accession numbers LC890385 (https://www.ncbi.nlm.nih.gov/nuccore/LC890385) and LC890386 (https://www.ncbi.nlm.nih.gov/nuccore/LC890386). The data are publicly accessible.
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Acknowledgements
The human iPSC line Windy was derived from a human embryonic lung fibroblast cell line (MRC-5) and obtained by Dr. Umezawa. Nagoya City University Institutional Review Board approved the protocol (No.70-20-0008).
Funding
This study was supported by JSPS KAKENHI Grant Number 20H03646, 24K02424 and 24K02425 for SS and ISS.
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E.S., Y.N., M.F., I.S.S., Y.K., and S.S. designed the study, E.S. and Y.N. conducted the investigation, E.S. and S.S. wrote the original draft, Y.N., M.F., I.S.S., T.I., D.I., Y.N., A.H., and Y.K. reviewed and edited the paper. All authors have read and agreed to the final manuscript.
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Sato, E., Nakamura, Y., Fujimoto, M. et al. Brain organoid models of SZT2-related disease reveal an overproduction of outer radial glial cells through mTORC1 activation. Sci Rep (2026). https://doi.org/10.1038/s41598-026-35733-w
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DOI: https://doi.org/10.1038/s41598-026-35733-w
