Drug-resistant 'Non-Lesional' Visual Sensitive Epilepsies of Childhood - Electroclinical Phenotype-Genotype Associations.

Background: Sporadic nonlesional intractable visual-sensitive epilepsies of childhood represent a challenging subset of epilepsies in terms of management and prognostication given a propensity to evolve as epileptic encephalopathy.

Objective: To study the genetic heterogeneity of drug-resistant visual sensitive epilepsy of childhood.

Methods: A retrospective chart review was conducted on patients in the pediatric age group between 2016 and 2018, with drug-resistant epilepsy (DRE) and video electro encephalography (VEEG) documented reflex photosensitivity, eye-condition sensitivity. Those patients who underwent genetic testing with targeted next-generation sequencing using an epilepsy gene panel were selected.

Results: During the study period, out of 96 patients who underwent genetic testing, 4 patients (4.17%) with sporadic DRE presented with clinical phenotypes ranging from myoclonic-atonic epilepsy, generalized epilepsy with eyelid myoclonia as well as febrile and unprovoked seizures, along with visual sensitivity. Video EEG documented abnormalities ranged from occipital, posterior-cortex and generalized discharges with "eyes-closed state" triggered, self-induced "smart-phone" triggered, photosensitive focal-onset and generalized myoclonic seizures. Accompanying developmental impairment was noted. These patients who were investigated with clinical exome sequencing were detected to have mutations in not only SCN1A genes (pathogenic exonic and intronic variants) but also CHD2 (pathogenic) and CACNA1H genes (a familial febrile-seizure susceptibility variant of unknown significance).

Conclusions: The series highlights the complex genetics of drug-resistant visual-sensitive epilepsy of childhood. Such genotype-phenotype associations throw light on the role of ion-channel and non-ion channel genes on reflex epileptogenesis in this group of patients.