Malformations of cortical development (MCD) are disorders causing epilepsy (classified by the World Health Organization as the most common serious brain disorder), cerebral palsy and developmental delay. Tuberous sclerosis complex (TSC) and focal cortical dysplasia (FCD) are two distinct but histologically similar brain malformations and the leading cause of focal epilepsy. The TSC and FCD lesions are characterised by focal disruption of cortical layering and the presence of abnormal cell types, including dysmorphic neurons. Electrophysiological studies have suggested that the dysmorphic neurons from the highly-dysplastic centre of the lesion are the seizure generators in both TSC and FCD. However, little is known about the properties of dysmorphic neurons or the qualities that convey seizure generating capabilities. The aim of this study was to identify the transcriptional profile of dysmorphic neurons to understand their epileptogenic properties.
We performed 10X Chromium single nuclei RNA-sequencing on ten biopsies of malformed brain tissue resected from five patients. A non-standard bioinformatics pipeline that paired highly-dysplastic centre vs mildly-dysplastic rim brain specimens was undertaken (4419±1150 cells/specimen; 1076±242 genes/cell). We performed a combined analysis of centre Vs rim for clustering and demonstrated a unique population of cells that expressed radial glia linage markers in biopsies from the centre, which may represent the dysmorphic neurons. Furthermore, these clusters formed unique trajectories suggestive of abnormal differentiation.
Our results provide the first description of the cellular composition of dysplastic lesions at single cell level. Characterising epileptogenic lesions at the single cell level will provide unprecedented knowledge of the mechanisms underlying seizure generation, leading to improved patient outcomes, and a greater understanding of brain development and function. Understanding seizure generation will provide unique opportunities to modify surgical practice and to identify novel pharmacological targets that will also be relevant to the broader 1% of population with epilepsy.