De Novo Heterozygous Pathogenic Variants in SCN2A as a Rare Cause of Malformation of Cortical Development
Abstract number :
1.011
Submission category :
1. Basic Mechanisms / 1A. Epileptogenesis of acquired epilepsies
Year :
2021
Submission ID :
1825910
Source :
www.aesnet.org
Presentation date :
12/4/2021 12:00:00 PM
Published date :
Nov 22, 2021, 06:51 AM
Authors :
Jerome Clatot, PhD - The Children's hospital of Philadelphia; Kevin Bender, PhD – Associate Professor, Neurology, UCSF Weill Institute for Neurosciences, UCSF; Alfred George, MD – Chair, Department of Pharmacology Director, Center for Pharmacogenomics Magerstadt Professor of Pharmacology Professor of Pharmacology, 4Department of Pharmacology, Northwestern University Feinberg School of Medicine, North Western University; Ethan Goldberg, MD. PhD. – Associate Professor, Neurology, Division of Neurology, Department of Pediatrics, and 2The Epilepsy NeuroGenetics Initiative, Children's Hospital of Philadelphia, Philadelphia, PA, USA, The Children's Hospital of Philadelphia; Katherine Helbig, PhD – senior genetic counselor, Division of Neurology, Department of Pediatrics, The Children's Hospital of Philadelphia; Christopher H. Thompson, PhD – ASSISTANT PROFESSOR, Health and Rehabilitation Sciences, Temple University; Roy Ben-Shalom – Associate Specialist, Neurology, UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA.
Rationale: SCN2A encodes the neuronal voltage-gated sodium channel a subunit Nav1.2, which is important for the generation and forward/backpropagation of action potentials in excitatory glutamatergic neurons of the cerebral cortex. Pathogenic variants of SCN2A are associated with a spectrum of neurodevelopmental disorders including autism spectrum disorder, benign familial neonatal and infantile seizures, and epileptic encephalopathy. However, the mechanisms whereby variation in SCN2A leads to disease remains incompletely understood and the full spectrum of SCN2A-related disease may not be fully delineated. Furthermore, while SCN2A (particularly the neonatal isoform) is highly expressed prenatally, the role of SCN2A in human fetal brain development is largely unknown. Here, we identified de novo heterozygous pathogenic variants in SCN2A in three patients with developmental and epileptic encephalopathy (DEE) as well as malformation of cortical development (MCD).
Methods: HEK-293 cells were co-transfected with the adult (A) or neonatal (N) isoform of wild-type (WT) or variant Nav1.2 along with b1 and b2 subunits and the biophysical characteristics of sodium currents were characterized using whole-cell voltage clamp recording. Parameters measured included peak current (pA/pF); voltage dependence of activation and steady-state inactivation; kinetics of inactivation and recovery from inactivation; and persistent current.
Results: Our results demonstrated complex/mixed functional effects of DEE/MCD-associated pathogenic variants in SCN2A. All three variants exhibited abnormal late/persistent channel opening, likely via different mechanisms. The neonatal Thr400Arg variant (Thr400Arg-N) exhibited a left (hyperpolarized) shift in the voltage dependence of activation and a rightward (depolarized) shift in the voltage-dependence of steady-state inactivation. Ile1640Asn-A and -N displayed a drastic rightward shift of steady state inactivation and decreased slope of the steady state inactivation curve, leading to large window current predicted to cause gain-of-function at the ion channel level. Additionally, this variant also displayed slower kinetics with delayed time to peak as well as slower fast and slow inactivation decay compared with wild-type channels. SCN2A-p.Met1770Leu-A also displayed a large rightward shift of steady-state inactivation along with slower inactivation decay, with a large persistent current for both Met1770Leu-A and –N.
Conclusions: All three SCN2A variants exhibited late channel opening by various mechanisms, either through a large shift in the voltage-dependence of steady-state inactivation creating a markedly enlarged window current, and/or by slowing of the inactivation kinetics. These results expand the clinical spectrum of SCN2A-related disorders, indicate that genetic variation in SCN2A is a rare cause of MCD, and suggest previously undescribed roles for SCN2A in fetal brain development.
Funding: Please list any funding that was received in support of this abstract.: NIH NINDS U54 NS108874 to A.L.G.; NIH NIMH R01 MH125978; March of Dimes Basil O’Connor Research Award and NIH NINDS K08 NS097633 and R01 NS119977 to E.M.G.
Basic Mechanisms