Abstract
The most characteristic syndrome related to KCNT1 is epilepsy of infancy with migrating focal seizures. Unifocal epilepsies have also been reported, the most common being sleep-related hypermotor epilepsy (SHE) of frontal origin. Only 10 cases of focal extrafrontal epilepsies with an insulo-opercular or temporal origin have been reported. Among these patients suffering from focal epilepsy, only seven underwent stereoelectroencephalography (S-EEG) describing focal or multifocal ictal onsets. We performed three S-EEGs and one S-EEG in two unrelated patients suffering from refractory magnetic resonance imagining-negative SHE with insulo-opercular seizures. None of the patients had any familial history of epilepsy or intellectual disability. They suffered from nocturnal seizures with stereotyped ictal symptoms suggestive of insulo-opercular SHE (IO-SHE). The four S-EEGs revealed multifocal, bilateral, and migrating ictal activity, whereas clinical ictal semiology remained stereotyped. These S-EEG findings led us to carry out genetic analysis, and a pathogenic missense variant of KCNT1 was found in each patient (p.Arg928Cys and p.Arg933His). Considering these two new patients, IO-SHE represents the second most frequent type of KCNT1-related focal epilepsy, and these S-EEG findings, never described before, suggest that migrating ictal activity might be a common feature of KCNT1-related epilepsy despite different syndromic presentations.