Scn3a, encoding the voltage-gated sodium channel subunit Nav1.3, is a gene primarily expressed in the central nervous system. Voltage-gated sodium channels are crucial for the initiation and propagation of action potentials and neural network activity [2].

Pathogenic variants in Scn3a can lead to a spectrum of neurodevelopmental disorders. Most patients with such variants have treatment-resistant epilepsy starting in the first year of life, along with severe or profound developmental delay. Malformations of cortical development are present in over 75% of affected individuals. Functionally, most pathogenic missense variants tested show a gain of channel function, with increased persistent current and/or a left-ward shift in voltage dependence of activation. However, loss-of-function variants have also been identified and are associated with increased seizure susceptibility. For example, a hypomorphic Scn3a allele (Scn3aHyp) in a gene trap mouse line led to increased susceptibility to electroconvulsive and chemiconvulsive induced seizures, as well as deficits in locomotor activity and motor learning [1,3].

In conclusion, Scn3a plays a vital role in normal neural function, with its dysfunction being strongly associated with epilepsy, severe developmental delay, and cortical malformations. Studies using gene-modified mouse models, such as those with a hypomorphic Scn3a allele, have been instrumental in revealing the role of Scn3a in seizure susceptibility and related neurological phenotypes, providing insights into the disease mechanisms associated with Scn3a-related disorders.