Phenotypic Spectrum and Long-term Outcome in Children With Genetic Causes of Early-onset Epileptic Encephalopathy
Authors: Hu Chunhui , Liu Deying , Luo Tian , Wang Yi , Liu Zhisheng 
Published: March 2021

Abstract
Background To explore the clinical phenotype and long-term outcome in children with genetic causes of early-onset epileptic encephalopathies. Methods The clinical data of 118 children between 2010 and 2020 was obtained and analyzed. The whole exome sequencing and copy number variation studies in family were used to find pathogenic mutations. The confirmed mutations were verified by Sanger sequencing. Results Among 118 patients, 39 patients were diagnosed with DS, 18 were WS, 3 were OS, 3 were EME, 2 were MMFSI, 1 was GLUT1 deficiency syndrome, 1 was Pyridoxine dependent epilepsy and 51 were non-symptomatic EOEEs. The initial EEG showed frequent multiple and multifocal sharp waves, spike waves, sharp slow waves or spike slow waves. In the later period, some transformed into infrequent discharging or normal EEG. 112 patients (112/118, 94.9%) showed normal brain MRI, and the remaining 6 had widened extracerebral space. In the later stage, 115 patients were re-examined with brain MRI 1 to 3 times, the widened gap became normal, only 2 had mild brain atrophy. After treatment, 42 patients (42/118, 35.6%) had seizure control. In EOEE-BS, 6 patients were found KCNQ2 mutations and the remaining mutations were SCN2A (n=2), STXBP1 (n=1). After treatment, only 2 patients had seizure control, 6 had uncontrolled seizures and 1 died. 7 patients with dyskinesia were found. 1 patient starting with a febrile convulsion was caused by HNRNPU mutation. SCN1A mutations were detected in 38 patients (38/118, 32.2%), representing the largest proportion. The second common mutations were KCNQ2 mutations in 9 patients. The third one was CDKL5 mutations in 8 patients. Genes associated with ionic channels represented the largest proportion (66/118, 55.9%), sodium channel potassium channel and calcium channel respectively. In WS, we detected SCN3A, SCN2A, SCN8A, CACNA1H, DEPDC5, MECP2, DYNC1H1, CDKL5, ALG11, CCDC88C, GABAA1, IL1RAPL1, RNASEH2B, SLC19A3, STXBP1, QARS, COL4A2 mutations. In addition to common gene mutations, we reported rare possible pathogenic genes: CCDC88C, IL1RAPL1, RNASEH2B and COL4A2 in WS. In non-syndromic genetic causes of EOEEs, we detected rare possible pathogenic genes: SETBP1, DPYD, CSNK2B and H3F3A. As for genetic modes, denovo heterozygous mutations account for the largest proportion (104/118, 88.1%). 3 patients with SMC1A mutations response to KD add-on therapy. VPA added treatment showed good effects on KCNB1 and PACS2 encephalopathy. LEV showed good effects on STXBP1, and OXC showed good effects on SCN8A encephalopathy. Conclusion The clinical manifestations of EOEE are variable, including dyskinesia. EOEE-BS usually response poorly to AEDS therapy. Although some patients achieve seizure-free, there is no remarkable improvement in their development. EOEEs starting with a febrile convulsion may be a special phenotype of HNRNPU related neurodevelopmental syndrome, similar to DS. We report rare possible pathogenic genes: CCDC88C, IL1RAPL1, RNASEH2B, COL4A2 in WS and detect rare possible pathogenic genes: SETBP1, DPYD, CSNK2B and H3F3A in non-syndromic genetic causes of EOEEs. Although genetic causes of EOEEs response poorly to AEDS treatment, we find that some gene mutation related EOEEs receive good effects on specific AEDS.