Brain somatic mutations in MTOR leading to focal cortical dysplasia

Area of Science:

• Neuroscience
• Molecular Genetics
• Epilepsy Research

Background:

• Focal cortical dysplasia type II (FCDII) is a significant cause of intractable epilepsy.
• The molecular genetic basis of FCDII and effective therapeutic targets remain poorly understood.
• Identifying the genetic underpinnings of FCDII is crucial for developing targeted treatments.

Purpose of the Study:

• To investigate the molecular genetic etiology of focal cortical dysplasia type II (FCDII).
• To identify potential therapeutic targets for intractable epilepsy associated with FCDII.
• To establish a causal link between MTOR gene mutations and FCDII pathogenesis.

Main Methods:

• Deep sequencing platforms were employed to analyze affected brain tissues from FCD patients.
• Somatic mutations in the MTOR gene were identified.
• In utero electroporation in mice was used to express mutant MTOR in the focal cortex, followed by neuropathological and seizure analysis, and assessment of rapamycin treatment efficacy.

Main Results:

• Somatic mutations in the MTOR gene, with allelic frequencies as low as 1%, were detected exclusively in affected brain tissues.
• These MTOR mutations led to hyperactivation of the MTOR kinase.
• Focal cortical expression of mutant MTOR in mice recapitulated key FCDII neuropathological features, including neuronal migration defects and cytomegalic neurons, and induced spontaneous seizures. Seizures and dysmorphic neurons were rescued by rapamycin treatment.

Conclusions:

• This study provides the first evidence that somatic activating mutations in the MTOR gene are a causative factor in FCDII.
• MTOR kinase hyperactivation due to these mutations drives the neuropathology of FCDII.
• MTOR inhibitors, such as rapamycin, represent a potential therapeutic strategy for intractable epilepsy in FCD patients.