Non‐epileptic stimulus‐sensitive myoclonus in a newborn with developmental and epileptic encephalopathy associated with the SCN8A gene

Developmental and epileptic encephalopathy (DEE) resulting from alterations in the SCN8A gene belongs to the group of channelopathies. The gene encodes the αsubunit of the voltage-dependent sodium channel Nav1.6, mainly expressed in the axon initial segments and the nodes of Ranvier for neuronal action potential initiation.1 Most variants are missense with GoF and result in DEE, and therefore, treatment with sodium blockers is the most effective.2 The DEE are often associated with hypotonia and abnormal movements including dystonia, ataxia, dyskinesia, and choreoathetosis; however, the presence of non-epileptic movements in SCN8A-DEE phenotypes remains poorly described. We present the case of a newborn with a novel variant in SCN8A exhibiting a DEE phenotype and non-epileptic stimulus-sensitive polymyoclonus, documented in video polygraphy.