The Epilepsy of Infancy With Migrating Focal Seizures: Identification of de novo Mutations of the KCNT2 Gene That Exert Inhibitory Effects on the Corresponding Heteromeric K Na 1.1/K Na 1.2 Potassium Channel.

The epilepsy of infancy with migrating focal seizures (EIMFS; previously called Malignant migrating partial seizures of infancy) are early-onset epileptic encephalopathies (EOEE) that associate multifocal ictal discharges and profound psychomotor retardation. EIMFS have a genetic origin and are mostly caused by de novo mutations in the KCNT1 gene, and much more rarely in the KCNT2 gene. KCNT1 and KCNT2 respectively encode the K _Na 1.1 (Slack) and K _Na 1.2 (Slick) subunits of the sodium-dependent voltage-gated potassium channel K _Na . Functional analyses of the corresponding mutant homomeric channels in vitro suggested gain-of-function effects. Here, we report two novel, de novo truncating mutations of KCNT2 : one mutation is frameshift (p.L48Qfs43), is situated in the N-terminal domain, and was found in a patient with EOEE (possibly EIMFS); the other mutation is nonsense (p.K564*), is located in the C-terminal region, and was found in a typical EIMFS patient. Using whole-cell patch-clamp recordings, we have analyzed the functional consequences of those two novel KCNT2 mutations on reconstituted K _Na 1.2 homomeric and K _Na 1.1/K _Na 1.2 heteromeric channels in transfected chinese hamster ovary (CHO) cells. We report that both mutations significantly impacted on K _Na function; notably, they decreased the global current density of heteromeric channels by ~25% (p.K564*) and ~55% (p.L48Qfs43). Overall our data emphasize the involvement of KCNT2 in EOEE and provide novel insights into the role of heteromeric K _Na channel in the severe KCNT2 -related epileptic phenotypes. This may have important implications regarding the elaboration of future treatment.
(Copyright © 2020 Mao, Bruneau, Gao, Becq, Jia, Xi, Shu, Wang, Szepetowski and Aniksztejn.)