Periodic Reporting for period 1 - CODICES (Exploring new genetic causes and pathological mechanisms of epileptic focal cortical dysplasia)
Reporting period: 2021-09-01 to 2023-08-31
Among FCD subtypes, FCD type 2 (FCD2) is characterized at the histopathological level by an abnormal structure of the cortex in the area affected by the disorder, where the characteristic six-layer structure appears disrupted. Abnormally large (cytomegalic) cells are also a classic hallmark of FCD2. Around 60% of FCD2 cases are due to inherited germline and/or de novo somatic mutations in genes regulating the mechanistic target of rapamycin (mTOR) pathway, which regulates cell growth, metabolism and proliferation. These mutations always cause a hyperactivation of the mTOR pathway that is thought to be associated with the aforementioned hallmarks of the disorder. Together with its focal nature, the role of somatic mutations in causing the disorder has recently defined FCD as a mosaic disorder of the brain. Despite these findings, a clear understanding of the consequences of mTOR pathway mutations, and especially mosaic mutations, in the development of the cerebral cortex and the insurgence of the disorder is still missing.
This project addressed the genetic, cellular and molecular mechanisms underlying the pathophysiology of FCD2 by modeling the disorder in vitro using 3-dimensional culture systems called cortical organoids that are generated from patient-derived human induced pluripotent stem cells (hiPSCs). This system has the advantage of reproducing developmental features specific to humans, and thus overcomes existing limitations encountered in mouse models, where the disorder is only partially reproducible.
Thus, our results will provide a clearer view especially of the developmental cellular and molecular mechanisms that are perturbed due to FCD2 mutations, and the consequences of pathogenic mosaicism for the development of the cortex. Our study will clarify the insurgence of this rare developmental mosaic disorder of the brain, while at the same time providing a first human-specific mosaic model of the disorder. This methodology will be exploited to prompt future studies that will address other epilepsy-related neurodevelopmental genes, but will also serve as a platform for the development of more targeted pharmacological treatments.
The results of this study will be published in a gold open access manuscript that is now in preparation, and will be presented to the scientific community in the framework of dedicated neuroscience, genetics and epilepsy conferences that are taking place in 2024.