In vivo, in vitro and in silico correlations of four de novo SCN1A missense mutations

• Published in: PloS one Vol. 14; no. 2; p. e0211901
• Main Authors: Nissenkorn, Andreea, Almog, Yael, Adler, Inbar, Safrin, Mary, Brusel, Marina, Marom, Milit, Bercovich, Shayel, Yakubovich, Daniel, Tzadok, Michal, Ben-Zeev, Bruria, Rubinstein, Moran
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 08.02.2019; Public Library of Science (PLoS)
• Subjects: Action Potentials; Amino Acid Substitution; Analysis; Bioinformatics; Biology and Life Sciences; Channel gating; Child; Child, Preschool; Cognitive ability; Cognitive Dysfunction - diagnosis; Cognitive Dysfunction - genetics; Cognitive Dysfunction - metabolism; Cognitive Dysfunction - physiopathology; Computational biology; Computational Biology - methods; Convulsions & seizures; Correlation; Correlation analysis; Diagnostic systems; Drug resistance; Early Diagnosis; Encephalopathy; Epilepsies, Myoclonic - diagnosis; Epilepsies, Myoclonic - genetics; Epilepsies, Myoclonic - metabolism; Epilepsies, Myoclonic - physiopathology; Epilepsy; Female; Functional analysis; Functional testing; Gene Expression; Genetic Predisposition to Disease; Genetic screening; Genetic testing; HEK293 Cells; Homology; Hospitals; Humans; In vivo methods and tests; Ion Transport; Life prediction; Male; Medicine; Medicine and Health Sciences; Missense mutation; Mutation; Mutation, Missense; Myoclonic epilepsy; Myoclonus; NAV1.1 Voltage-Gated Sodium Channel - chemistry; NAV1.1 Voltage-Gated Sodium Channel - genetics; NAV1.1 Voltage-Gated Sodium Channel - metabolism; Neurobiology; Neurology; Neurons; Neurosciences; Patch-Clamp Techniques; Pathogenicity; Pathogens; Pediatrics; Phenotypes; Precision Medicine; Prognosis; R&D; Research & development; Research and Analysis Methods; Seizing; Seizures; Severity of Illness Index; Social Sciences; Sodium; Sodium channels (voltage-gated); Software patches; Structural Homology, Protein; Transfection; Israel; Tel Aviv Israel
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0211901

Mutations in the SCN1A gene, which encodes for the voltage-gated sodium channel NaV1.1, cause Dravet syndrome, a severe developmental and epileptic encephalopathy. Genetic testing of this gene is recommended early in life. However, predicting the outcome of de novo missense SCN1A mutations is difficult, since milder epileptic syndromes may also be associated. In this study, we correlated clinical severity with functional in vitro electrophysiological testing of channel activity and bioinformatics prediction of damaging mutational effects. Three patients, bearing the mutations p.Gly177Ala, p.Ser259Arg and p.Glu1923Arg, showed frequent intractable seizures that had started early in life, with cognitive and behavioral deterioration, consistent with classical Dravet phenotypes. These mutations failed to produce measurable sodium currents in a mammalian expression system, indicating complete loss of channel function. A fourth patient, who harbored the mutation p.Met1267Ile, though presenting with seizures early in life, showed lower seizure burden and higher cognitive function, matching borderland Dravet phenotypes. In correlation with this, functional analysis demonstrated the presence of sodium currents, but with partial loss of function. In contrast, six bioinformatics tools for predicting mutational pathogenicity suggested similar impact for all mutations. Likewise, homology modeling of the secondary and tertiary structures failed to reveal misfolding. In conclusion, functional studies using patch clamp are suggested as a prognostic tool, whereby detectable currents imply milder phenotypes and absence of currents indicate an unfavorable prognosis. Future development of automated patch clamp systems will facilitate the inclusion of such functional testing as part of personalized patient diagnostic schemes.