Abstracts

Rationale: Neocortical thinning in mesial temporal lobe epilepsy (MTLE) extends to several brain regions beyond the ipsilateral epileptogenic zones. Such widespread thinning has been attributed to the neurotoxic effect of the spreading seizures originating in the ipsilateral mesial temporal regions. However, it remains unknown whether cortical thinning exists in relevant brain regions prior to the onset of seizures, and whether its presence represents risk factor for seizure development in high risk individuals. In this study, we explored cerebral cortex thickness patterns in asymptomatic siblings of patients with MTLE. Methods: High resolution T1-weighted magnetic resonance images (MRI) were acquired from 50 asymptomatic, same-gender, full siblings of patients with unilateral MTLE associated with hippocampal sclerosis (HS), and 40 healthy control subjects. A surface-based morphometry method (FreeSurfer) was applied to process the images and quantify cerebral cortex thickness in all individuals. Group differences in cortical thickness were determined using a generalized linear model with age and gender included as co-variates. Results: Compared to controls, the asymptomatic siblings of MTLE patients displayed significant localized thinning of the parahippocampal gyrus bilaterally. Further, significant cortical thinning was noted in the right fusiform gyrus. These localized thinning patterns were independent of the normal age-related changes in cerebral cortical thickness. Conclusions: The asymptomatic siblings of patients with MTLE display cortical thinning in localized regions of the mesial temporal cortex. As neuroanatomical trait, such cortical thinning patterns may represent an intermediate phenotype that is relevant to the underlying mechanisms of this epilepsy syndrome.