Tau pathology in epilepsy: emerging mechanisms and translational opportunities.

The onset of epilepsy in adulthood occurs most commonly after 55 years of age. Given the ageing global population, this disorder represents an increasing burden on healthcare and society. The bidirectional link between epilepsy and dementia is a focus of intense research with underlying tau pathology highlighted as a potential mechanistic link. In this review, we examine the evidence for tau-related neurodegenerative processes in epilepsy beginning with how changes in biochemical and structural properties of the tau protein can lead to abnormal phosphorylation and pathological aggregation. We consider the role of tau in seizure occurrence and cognitive difficulties in experimental animal epilepsy models to human epileptic syndromes. Seizure prevalence is evaluated across established primary and secondary tauopathies to understand the associated hyperexcitability phenotype. We discuss the use of neurophysiology, metabolic imaging and novel fluid biomarkers as non-invasive measures of potential underlying neurodegeneration in epilepsy. It may, for example, be that these can be combined with remote measures of cognition and other physiological parameters to provide accurate longitudinal monitoring of cognition and underlying pathology. We also explore clinical trials that have targeted pathological tau accumulation in neurodegenerative conditions and consider an ongoing clinical study with sodium selenate, an enhancer of protein phosphatase enzyme PP2A, in people with epilepsy. These efforts signify a novel disease-modifying era with treatments that reduce seizures and modify cognitive outcomes in people with epilepsy. Our analysis of the literature underscores the need for more in-depth characterization of tau pathology, at biochemical and structural levels, in brain tissue and peripheral samples from people with epilepsy as an important step to deciphering the role of tau in the pathogenesis of epilepsy and related disorders. Examining the relationships between tau pathology and cognitive impairment in those with epilepsy provides critical perspectives on a potential causal tau pathomechanism that may have important roles in epileptogenesis and dementia.