Genetic and Clinical Features of SCN8A Developmental and Epileptic Encephalopathy T
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Epilepsy Research 158 (2019) 106222 Contents lists available at ScienceDirect Epilepsy Research journal homepage: www.elsevier.com/locate/epilepsyres Genetic and clinical features of SCN8A developmental and epileptic encephalopathy T Hyo Jeong Kima, Donghwa Yangb, Se Hee Kimb, Borahm Kimc, Heung Dong Kimb, Joon Soo Leeb, Jong Rak Choic, Seung-Tae Leec, Hoon-Chul Kangb,* a Department of Pediatrics, Gachon University Gil Medical Center, Gachon University College of Medicine, 21565, Namdong-daero 774-21, Namdong-gu, Incheon, Republic of Korea b Division of Pediatric Neurology, Epilepsy Research Institute, Severance Children’s Hospital, Department of Pediatrics, Yonsei University College of Medicine, 03722 Yonsei-ro 50-1, Seodaemun-gu, Seoul, Republic of Korea c Department of Laboratory Medicine, Severance Hospital, Yonsei University College of Medicine, 03722 Yonsei-ro 50-1, Seodaemun-gu, Seoul, Republic of Korea ARTICLE INFO ABSTRACT Keywords: Objective: We aim to delineate the genetic and clinical features of SCN8A developmental and epileptic en- SCN8A cephalopathy. Developmental and epileptic encephalopathy Methods: Nine patients with SCN8A developmental and epileptic encephalopathy were included in this study. Sodium channel blockers Genetic and clinical features and effectiveness of sodium channel blockers were assessed in patients who were confirmed with SCN8A mutations. Results: The onset of seizures ranged from the neonatal period to 18 months of age. Seizure types were diverse and predominantly involved focal seizures or spasms. The most common initial epilepsy syndrome was West syndrome in four patients, followed by neonatal-onset focal seizures in three patients and unclassified focal epilepsy in two patients. Electroencephalograms (EEGs) showed slow and disorganized background and epi- leptiform abnormalities with occipital predominance. Six patients presented intractable seizures including one patient with recurrent nonconvulsive status epilepticus. Sodium channel blockers were effective in seven pa- tients among eight patients given them. All patients showed developmental delay or regression. Severe hypo- tonia or ataxia was also presented in some patients. Microcephaly was also characteristic. De novo missense mutations in SCN8A were found in the inactivation gate, C-terminal, loop 2, and transmembrane segments (S1, 4, 5, and 6). There was no correlation between the location of the mutation in the protein and phenotype or response to sodium channel blockers. Conclusion: SCN8A developmental and epileptic encephalopathy presents intractable seizures including spasms, focal seizures, neonatal status epilepticus, and nonconvulsive status epilepticus. Sodium channel blockers were effective irrelevant to the location of the mutation in the protein. 1. Introduction developmental epileptic encephalopathy (Gardella et al., 2018; Larsen et al., 2015; Ohba et al., 2014). SCN8A mutations are also known to be Voltage-gated sodium channels play a key role in electrical signaling associated with movement disorders or even early mortality (Gardella by their action potential initiation and propagation in the membranes et al., 2016; Johannesen et al., 2018; Pons et al., 2018; Xiao et al., of neurons and other electrically excitable cells (Catterall, 2000). 2018). SCN8A is one of nine genes that encodes a voltage-gated sodium Early infantile epileptic encephalopathy type 13 (EIEE13, OMIM channel α subunit. SCN8A encodes the sodium channel Nav1.6, which is #614,558) is a recently defined severe developmental epileptic en- widely expressed in the brain, where it plays a role in regulation of cephalopathy syndrome caused by de novo gain-of-function mutations neuronal excitability (Caldwell et al., 2000). of SCN8A, which was first identified in 2012 (Veeramah et al., 2012). SCN8A mutations are associated with a wide spectrum of epilepsy As SCN8A mutations can cause diverse epilepsy phenotypes, phenotypic phenotypes, ranging from benign familial infantile epilepsy (Anand classification is crucial for predicting prognosis and guiding therapeutic et al., 2016; Bagnasco et al., 2018; Gardella et al., 2016) to severe strategies. ⁎ Corresponding author. E-mail address: [email protected] (H.-C. Kang). https://doi.org/10.1016/j.eplepsyres.2019.106222 Received 23 May 2019; Received in revised form 13 October 2019; Accepted 19 October 2019 Available online 22 October 2019 0920-1211/ © 2019 Elsevier B.V. All rights reserved. H.J. Kim, et al. Epilepsy Research 158 (2019) 106222 Table 1 SCN8A mutations and patient responses to sodium channel blockers. Pt Nucleotide change Amino acid change Mutation type Protein location SCB response* 1 c.4423 G > A p.Gly1475Arg Missense Inactivation gate Effective2 2 c.2549 G > A p.Arg850Gln Missense DII S4 Effective2 3 c.782 G > T p.Cys261 Phe Missense DI S5 Effective2 4 c.424A > G p.Ile142Val Missense DI S1 Effective2 5 c.5614C > T p.Arg1872Trp Missense C-terminal Effective2 6 c.4475 T > C p.Met1494Thr Missense Inactivation gate No trial 7 c.5276A > C p.Asn1759Thr Missense DIV S6 Ineffective3 8 c.2911C > G p.Leu971Val Missense DII S6 Effective1 9 c.2934C > A p.Ser978Arg Missense Loop2 Effective1 D, domain; SCB, sodium channel blocker; *1, seizure free; 2, seizure reduction; 3,noeffect; 4, worsening. Herein, we delineated the genetic and clinical features in patients were previously published (Ko et al., 2018) in less detail and four pa- with SCN8A developmental and epileptic encephalopathy who were tients were unpublished. diagnosed through targeted gene-panel sequencing. 3.1. Mutation analysis 2. Methods We identified nine patients with heterozygous, pathogenic, missense 2.1. Patients mutations. All were different variants and were predicted to be dele- terious by prediction tools (PolyPhen-2, SIFT, MutationTaster). Four Patients with SCN8A developmental and epileptic encephalopathy variants (patient 1,2,4,5) have been previously reported to be asso- fi were identi ed from a cohort of 730 pediatric patients with early-onset ciated with SCN8A developmental and epileptic encephalopathy. developmental epileptic encephalopathy of unknown etiology at Parental studies were done in seven patients (patients 1, 3, 4, 5, 6, 8, ’ Severance Children s Hospital. The patients were tested using a targeted and 9); all of them showed de novo mutations. In patient 7, parental – gene-panel sequencing between 2015 2018. One patient with SCN8A testing was performed only in her mother due to family matters, who developmental and epileptic encephalopathy from Gachon University showed no mutation in SCN8A. The mutations were found in in- Gil Medical Center was also included. activation gate, Loop2, C-terminal, and transmembrane segments (S1, 4, 5, and 6). Sodium channel blockers were tried in eight patients; seven 2.2. Clinical data patients showed effectiveness unrelated to the location of the mutation in the protein (Table 1, Fig. 1). Detailed clinical features were retrospectively reviewed. Clinical data included demographics, age of seizure onset, seizure type, classi- 3.2. Clinical features of SCN8A developmental and epileptic fication of epilepsy syndrome, treatment of epilepsy, response to so- encephalopathy dium channel blockers, head circumference, development, typical clinical features, EEG data, and brain MRI. Seizure types and epilepsy The patients ranged in age from 5 months to 9 years. The onset of syndromes were classified according to the 2017 International League seizures ranged from 1 day to 18 months of age. Seizure semiology was Against Epilepsy classification guidelines (Scheffer et al., 2017). Initial variable and included epileptic spasms, focal seizures, generalized tonic epilepsy syndromes were selected if they changed over time. Response clonic seizures, myoclonic absence seizures, and nonconvulsive status to sodium channel blockers was considered effective if seizure fre- epilepticus (NCSE). The most common initial epilepsy syndrome was quencies were decreased more than 50% from baseline. West syndrome in four patients. One patient showed neonatal focal seizures evolving to West syndrome, two patients showed neonatal 2.3. Mutation analysis status epilepticus, and two patients showed unclassified focal epileptic encephalopathy (Table 2). Six patients presented intractable seizures, One hundred seventy-two genes, including SCN8A, associated with including one patient with recurrent nonconvulsive status epilepticus; developmental epileptic encephalopathy were included in our targeted three of these patients reached seizure-free status. Sodium channel gene panel; the genes are listed in the Appendix. Genomic DNA was blockers were tried in eight patients and were effective in seven patients extracted from leukocytes using the QIAamp Blood DNA mini kit and ineffective in one patient. Ketogenic diets were tried in five pa- (Qiagen, Hilden, Germany). The pooled libraries were sequenced using tients; and it was effective in only one patient. Epilepsy surgery was a MiSeq sequencer (Illumina, San Diego, CA, USA) and the MiSeq performed on one patient (patient 3), involving corpus callosotomy and Reagent Kit v2 (300 cycles). Sequencing data were aligned against right temporal disconnection. Patient 3 showed intractable seizures in appropriate reference sequences and analyzed using Sequencher 5.3 spite of multiple antiepileptic drugs, ketogenic diet, and corpus callo- software (Gene Codes Corp., Ann Arbor, MI, USA). Parental studies sotomy tried at 6 years. After corpus callosotomy, epileptic discharges were performed by Sanger sequencing on a 3730