De Novo Missense KCN3A Variant Cause Developmental and Epileptic Encephalopathy
Abstract number :
V.096
Submission category :
12. Genetics / 12A. Human Studies
Year :
2021
Submission ID :
1825793
Source :
www.aesnet.org
Presentation date :
12/9/2021 12:00:00 PM
Published date :
Nov 22, 2021, 06:50 AM
Authors :
Meng-Han Tsai, MD, PhD - Kaohsiung Chang Gung Memorial Hospital; Chia-Hua Lo, MS - National Yang Ming Chiao Tung University; Eric Hwang, PhD - A/Prof, National Yang Ming Chiao Tung University,; Ya-Jean Wang, PhD - Assist Prof, Minghsin University of Science and Technology
Rationale: De novo pathogenic variants have been found to be an important cause of developmental and epileptic encephalopathy (DEE). Despite many genes having been reported to cause DEE, there are still patients with DEE where the etiology remains unknown. Novel DEE genes await to be identified.
Methods: Whole exome sequencing (WES) Trio was performed on the proband and family and followed by Sanger sequencing validation to identified de novo pathogenic variants. Whole cell voltage clamping was performed to characterize the functional properties of overexpressed mutant and wild type KCNA3 constructs.
Results: The proband had seizure onset with fever at age of 1. He later developed afebrile focal and bilateral tonic-clonic seizures after two febrile seizures. Electroencephalogram showed multiple focal epileptiform discharges over bilateral hemispheres. Brain magnetic resonance imaging was unremarkable. He also had developmental delay (walk at 1y8m and no speech) and severe intellectual disability. He continues to have an average of 3 seizures per month despite two anti-seizure medications control (Valproate and Levetiracetam). There is no family history of seizures or epilepsy.
WES Trio identified a de novo missense variant in KCNA3 gene (Figure 1). There was no published case of KCNA3 caused epilepsy so far. The amino acid located in the PVP motif that is located in the pathogenic variant enriched region (PER) reported by Perez-Palma et al. 2019. The PVP motif locates at the bottom of the S6, it functions as a hinge of the bundle-crossing gate of the potassium channel. Therefore, the mutation is predicted to affect the opening/closing of the potassium channel.
Potassium channels are important determinants of seizure susceptibility. We thus generate wild type and mutant constructs of KCNA3 using site-direct mutagenesis. HEK293T cells expressing wild-type or mutant KCNA3 were generated using lentivirus-based strategy. The cells were then used for electrophysiological recording. Whole-cell recordings reveal that the mutant Kv1.3 (KCNA3) channel exhibits a decreased outward current compared to wild type. Voltage-ramping also showed a decreased response of mutant compared to wild type (Figure 2).
Conclusions: Overall, these preliminary genetic and electrophysiological studies suggest that KCNA3 is a novel epilepsy gene for developmental and epileptic encephalopathy. Pathogenic variant cause loss of Kv1.3 function.
Funding: Please list any funding that was received in support of this abstract.: The research is supported by the Ministry of Science and Technology (MOST), Taiwan; National Health Research Institute (NHRI), Taiwan; Kaohsiung Chang Gung Memorial Hospital, Taiwan.
Genetics