Genomic analysis and in vivo functional validation of brain somatic mutations leading to focal cortical malformations

Abstract

Focal cortical malformation (FCM), such as focal cortical dysplasia (FCD) and hemimegalencephaly (HME), is a major developmental brain malformation in the cerebral cortex leading to intractable epilepsy. The sporadic occurrence of most FCM and histologic characteristics of surgically resected brain tissue showing scattered dysmorphic cells suggest that FCM might be caused by a somatic mutation in an area affecting brain development. Indeed, recent genomic studies of these conditions have shown that low-frequency somatic mutations in PI3K-AKT-mTOR pathway genes are a major genetic cause of FCM. In addition, functional validation using an in vivo disease model not only confirmed the causality of the identified somatic mutations but also helped to reveal their molecular genetic mechanisms. Here, we highlight the key points to be considered regarding the application of sequencing methods and bioinformatics analysis to identify brain somatic mutations with a low allelic frequency in FCM patients. In addition, we describe the generation of an in vivo disease model recapitulating the pathologic phenotype of FCM such as dysmorphic neurons, migration defects, and electrographic seizures. Our goal is to provide guidelines for the analysis of sequencing data and functional validation using a disease model of FCM caused by somatic mutations.