The potential role of micro-RNA-211 in the pathogenesis of sleep-related hypermotor epilepsy.

Sleep-related hypermotor epilepsy (SHE) is a rare epileptic syndrome characterized by epileptic seizures which occur during the non-rapid eye movement (NREM) stage of sleep. It manifests with hypermotor semiology resembling violent limb movements and an asymmetric tonic-dystonic posture. The genes which are responsible for the autosomal dominant form of SHE (ADSHE) and whose function is to code the sub-unit of the neuronal acetylcholine receptor are well known. Considering that ADSHE is a prototype of SHE, it is thought that the dysfunction of the cortico-subcortical cholinergic network, which regulates the cycle of sleep, has a key role in the epileptogenesis of this syndrome. Namely, studies to date, have shown that the hypercholinergic activity is sufficient for the development of epileptic seizures, even though the exact mechanism remains to be elucidated. NREM parasomnias are sleep disorders that are the most difficult to differentiate from SHE due to a similar clinical presentation. Considering the clinical similarities, NREM occurrence and probable genetic connection, it is considered that fundamentally, both of these conditions share a common pathophysiological mechanism i.e. cholinergic dysfunction. The main difference between SHE and NREM parasomnias are the genuine epileptic seizures that are responsible for the semiology in SHE. These genuine seizures are not present in NREM parasomnias. Why this is so, remains to be elucidated. Considering that animal studies have shown that dynamic changes and the decreased levels of microRNA-211 contribute to epileptic seizures and to changes in cholinergic pathways, our hypothesis is that epileptic seizures and the development of epileptogenesis in SHE are a consequence of cholinergic dysfunction and decreased levels of microRNA-211 as opposed to NREM parasomnias where there is a stable level of microRNA-211, preventing epileptogenesis despite the cholinergic system dysfunction.