NAPB and developmental and epileptic encephalopathy: Description of the electroclinical profile associated with a novel pathogenic variant.

Developmental and epileptic encephalopathies (DEE) are a group of neurodevelopmental disorders characterized by epileptic seizures associated with developmental delay or regression. DEE are genetically heterogeneous, and the proteins involved play roles in multiple pathways such as synaptic transmission, metabolism, neuronal development or maturation, transcriptional regulation, and intracellular trafficking. We performed whole exome sequencing on a consanguineous family with three children presenting an early onset (<6 months) with clusters of seizures characterized by oculomotor and vegetative manifestations, with an occipital origin. Before 1 year of age, interictal electroencephalographic recordings were well organized and neurodevelopment was unremarkable. Then, a severe regression occurred. We identified a novel homozygous protein-truncating variant in the NAPB (N-ethylmaleimide-sensitive fusion [NSF] attachment protein beta) gene that encodes the βSNAP protein, a key regulator of NSF-adenosine triphosphatase. This enzyme is essential for synaptic transmission by disassembling and recycling proteins of the SNARE complex. Here, we describe the electroclinical profile of each patient during the disease course. Our findings strengthen the association between biallelic variants in NAPB and DEE and refine the associated phenotype. We suggest including this gene in the targeted epilepsy gene panels used for routine diagnosis of unexplained epilepsy.