Familial mesial temporal lobe epilepsy: clinical spectrum and genetic evidence for a polygenic architecture.

Abstract

Familial mesial temporal lobe epilepsy (FMTLE) is an important focal epilepsy syndrome; its molecular genetic basis is unknown. Clinical descriptions of FMTLE vary between a mild syndrome with prominent déjà vu to a more severe phenotype with febrile seizures and hippocampal sclerosis. We aimed to refine the phenotype of FMTLE by analyzing a large cohort and asked whether common risk variants for focal epilepsy and/or febrile seizures, measured by polygenic risk scores (PRS), are enriched in individuals with FMTLE. We studied 134 families with ≥2 first or second-degree relatives with temporal lobe epilepsy (TLE), with clear mesial ictal semiology required in at least one individual. PRS were calculated for 227 FMTLE cases, 124 unaffected relatives and 16,077 population controls. Age of FMTLE onset ranged from 2.5-70 years (median = 18, IQR = 13-28 years). The most common focal seizure symptom was déjà vu (62% of cases), followed by epigastric rising sensation (34%), and fear or anxiety (22%). The clinical spectrum included rare cases with drug-resistance and/or hippocampal sclerosis. FMTLE cases had a higher mean Focal Epilepsy PRS than population controls (OR 1.24, 95% CI 1.06, 1.46, p = 0.007); in contrast, no enrichment for the Febrile Seizure PRS was observed. FMTLE is a generally mild drug-responsive syndrome with déjà vu being the commonest symptom. In contrast to dominant monogenic focal epilepsy syndromes, our molecular data support a polygenic basis for FMTLE. Furthermore, the PRS data suggest that sub-genome-wide significant focal epilepsy GWAS SNPs are important risk variants for FMTLE. This article is protected by copyright. All rights reserved.