Discovery of Novel Molecular Abnormalities Underlying Non-Lesional Focal Epilepsy

Investigator: Joseph L. Derisi, PhD
Sponsor: Columbia University

Location(s): United States


Non-lesion focal epilepsy (NLFE) consists of recurrent seizures that arise from an area of the brain that has no apparent abnormality on MRI. We propose to examine brain tissue removed at epilepsy surgery from individuals with NLFE in order to identify whether somatic mutation- genetic abnormalities arising only in brain cells-or the presence of foreign microbial DNA or RNA (e.g. from viral infection) underlies this difficult t treat form of epilepsy. Discovery of the role of mutation or infection could influence new strategies for treatment and prevention.

The goal of this proposal is to explore the role of molecular abnormalities-somatic mutation, the presence of microbial nucleic acids, or both--underlying non-lesion focal epilepsy (NLFE). Epilepsy affects nearly 1% of the world's population and 1/3 of patients do not respond to currently available anticonvulsant medications. For these patients the best hope for seizure control comes from epilepsy surgery with resection of the seizure focus, when a focus can be identified. In patients for whom a causative lesion is clearly demonstrable on MRI, 60-80% of patients are seizure-free after surgery. In patients with clear focal epilepsy with no identifiable MRI lesion, surgical cure is less common, ranging from 30-50%. We propose that the problem of NLFE is one of resolution-that the abnormalities may not be visible on MRI but are present at the molecular level, in one or both of two forms: 1) somatic mutation, in cells restricted to brain and 2) the presence of microbial, e.g. viral nucleic acids, which may cause molecular abnormalities and influence epilepsy onset. There is some evidence to suggest that somatic mutation plays a role in epilepsies resulting from developmental structural lesions such as hemimegalencephaly, but somatic mutation has not yet been shown to occur in non-lesion epilepsies. The role of viral infection in epilepsy and developmental molecular lesions of the cortex has been suggested based on the detection of HHV6 in brain tissue from temporal lobe epilepsy patients with mesial temporal sclerosis and with the recent discovery of human papilloma virus in areas of focal cortical dysplasia, a developmental malformation strongly associated with epilepsy. The broader role of viruses in NLFE has not been demonstrated, nor the role of other pathogens. We will investigate whether somatic mutations and microbial nucleic acids are present in the seizure foci of individuals with epilepsy who undergo surgery, using next generation sequencing approaches to identify these molecular abnormalities in resected brain tissue. We will accomplish this using a systems biology approach, integrating state-of-the-art cortical intraoperative recordings to identify the seizure focus, co-registered with clinical, histopathology, and molecular sequence data. We will thereby create a repository of NLFE brain tissue with detailed phenotypic data which will be the first of its kind. Proving that seizures can arise from somatic mutations or infection without altering brain macrostructure would shift the paradigm for understanding epileptogenesis, and could lead to identification of novel biomarkers and treatments.