Identification of Novel Mosaic Variants in Focal Epilepsy-Associated Patients' Brain Lesions

Focal cortical dysplasia type III (FCDIII) is a rare and complex condition associated with drug-resistant epilepsy and often characterized by cortical lamination abnormalities, along with a variety of neoplasms and vascular abnormalities.

This study aimed to elucidate the genetic architecture underlying FCDIII through the use of whole-exome sequencing (WES) of brain and peripheral blood samples from 19 patients who had been diagnosed with FCDIII.

Variants were identified through a series of machine-learning-based detection and functional prediction methods and were not previously associated with FCDIII. Mosaic fraction scores of these variants validated the variants' pathogenicity, and in silico and gene ontology enrichment analyses demonstrated that these variants had severe destabilizing effects on protein structure.

We reported ten novel pathogenic somatic missense and loss of function variants across eight genes, including CNTNAP2, ACY1, SERAC1, and BRAF. Genetic alterations were linked to clinical manifestations, such as encephalopathies and intellectual disabilities, thereby emphasizing their role as molecular drivers of FCDIII.

We demonstrated that next-generation sequencing-based mosaic variant-calling pipelines are useful for the genetic diagnosis of FCDIII, opening up avenues for targeted therapies, yet further research is required to validate these findings and examine their therapeutic implications.