Genotype-phenotype correlations in SCN8A-related disorders reveal prognostic and therapeutic implications

We report detailed functional analyses and genotype-phenotype correlations in 433 individuals carrying disease-causing variants in SCN8A, encoding the voltage-gated Na+ channel NaV1.6. Five different clinical subgroups could be identified: 1) Benign familial infantile epilepsy (BFIE) (n=17, normal cognition, treatable seizures), 2) intermediate epilepsy (n=36, mild ID, partially pharmacoresponsive), 3) developmental and epileptic encephalopathy (DEE, n=191, severe ID, majority pharmacoresistant), 4) generalized epilepsy (n=21, mild to moderate ID, frequently with absence seizures), and 5) affected individuals without epilepsy (n=25, mild to moderate ID). Groups 1-3 presented with early-onset (median: four months) focal or multifocal seizures and epileptic discharges, whereas the onset of seizures in group 4 was later (median: 39 months) with generalized epileptic discharges. The epilepsy was not classifiable in 143 individuals. We performed functional studies expressing missense variants in ND7/23 neuroblastoma cells and primary neuronal cultures using recombinant tetrodotoxin insensitive human NaV1.6 channels and whole-cell patch clamping. Two variants causing DEE showed a strong gain-of-function (GOF, hyperpolarising shift of steady-state activation, strongly increased neuronal firing rate), and one variant causing BFIE or intermediate epilepsy showed a mild GOF (defective fast inactivation, less increased firing). In contrast, all three variants causing generalized epilepsy induced a loss-of-function (LOF, reduced current amplitudes, depolarising shift of steady-state activation, reduced neuronal firing). Including previous studies, functional effects were known for 165 individuals. All 133 individuals carrying GOF variants had either focal (76, groups 1-3), or unclassifiable epilepsy (37), whereas 32 with LOF variants had either generalized (14), no (11) or unclassifiable (5) epilepsy; only two had DEE. Computational modeling in the GOF group revealed a significant correlation between the severity of the electrophysiological and clinical phenotypes. GOF variant carriers responded significantly better to sodium channel blockers (SCBs) than to other anti-seizure medications, and the same applied for all individuals of groups 1-3. In conclusion, our data reveal clear genotype-phenotype correlations between age at seizure onset, type of epilepsy and gain- or loss-of-function effects of SCN8A variants. Generalized epilepsy with absence seizures is the main epilepsy phenotype of LOF variant carriers and the extent of the electrophysiological dysfunction of the GOF variants is a main determinant of the severity of the clinical phenotype in focal epilepsies. Our pharmacological data indicate that SCBs present a therapeutic treatment option in early onset SCN8A-related focal epilepsy.

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Genotype-phenotype correlations in SCN8A-related disorders reveal prognostic and therapeutic implications

Brain ◽

10.1093/brain/awab321 ◽

2021 ◽

Author(s):

Katrine M Johannesen ◽

Yuanyuan Liu ◽

Mahmoud Koko ◽

Cathrine E Gjerulfsen ◽

Lukas Sonnenberg ◽

...

Keyword(s):

Steady State ◽

Neurodevelopmental Disorder ◽

Neuronal Firing ◽

Na Channel ◽

Neuronal Cultures ◽

Loss Of Function ◽

Absence Seizures ◽

Clinical Phenotypes ◽

Epileptiform Discharges ◽

Generalized Epilepsy

Abstract We report detailed functional analyses and genotype-phenotype correlations in 392 individuals carrying disease-causing variants in SCN8A, encoding the voltage-gated Na+ channel NaV1.6, with the aim of describing clinical phenotypes related to functional effects. Six different clinical subgroups could be identified: 1) Benign familial infantile epilepsy (BFIE) (n = 15, normal cognition, treatable seizures), 2) intermediate epilepsy (n = 33, mild ID, partially pharmaco-responsive), 3) developmental and epileptic encephalopathy (DEE, n = 177, severe ID, majority pharmaco-resistant), 4) generalized epilepsy (n = 20, mild to moderate ID, frequently with absence seizures), 5) unclassifiable epilepsy (n = 127), and 6) neurodevelopmental disorder without epilepsy (n = 20, mild to moderate ID). Groups 1–3 presented with focal or multifocal seizures (median age of onset: four months) and focal epileptiform discharges, whereas the onset of seizures in group 4 was later (median: 42 months) with generalized epileptiform discharges. We performed functional studies expressing missense variants in ND7/23 neuroblastoma cells and primary neuronal cultures using recombinant tetrodotoxin-insensitive human NaV1.6 channels and whole-cell patch-clamping. Two variants causing DEE showed a strong gain-of-function (GOF, hyperpolarising shift of steady-state activation, strongly increased neuronal firing rate), and one variant causing BFIE or intermediate epilepsy showed a mild GOF (defective fast inactivation, less increased firing). In contrast, all three variants causing generalized epilepsy induced a loss-of-function (LOF, reduced current amplitudes, depolarising shift of steady-state activation, reduced neuronal firing). Including previous studies, functional effects were known for 170 individuals. All 136 individuals carrying a functionally tested GOF variant had either focal (97, groups 1–3), or unclassifiable epilepsy (39), whereas 34 with a LOF variant had either generalized (14), no (11) or unclassifiable (6) epilepsy; only three had DEE. Computational modeling in the GOF group revealed a significant correlation between the severity of the electrophysiological and clinical phenotypes. GOF variant carriers responded significantly better to sodium channel blockers (SCBs) than to other anti-seizure medications, and the same applied for all individuals of groups 1–3. In conclusion, our data reveal clear genotype-phenotype correlations between age at seizure onset, type of epilepsy and gain- or loss-of-function effects of SCN8A variants. Generalized epilepsy with absence seizures is the main epilepsy phenotype of LOF variant carriers and the extent of the electrophysiological dysfunction of the GOF variants is a main determinant of the severity of the clinical phenotype in focal epilepsies. Our pharmacological data indicate that SCBs present a treatment option in SCN8A-related focal epilepsy with onset in the first year of life.

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Seizure Exacerbation by Antiepileptic Drugs

Epilepsy Currents ◽

10.1111/j.1535-7511.2005.00061.x ◽

2005 ◽

Vol 5 (5) ◽

pp. 192-193 ◽

Cited By ~ 2

Author(s):

Jacqueline A. French

Keyword(s):

Antiepileptic Drugs ◽

De Novo ◽

Focal Epilepsy ◽

Juvenile Myoclonic Epilepsy ◽

Absence Epilepsy ◽

Absence Seizures ◽

Incorrect Diagnosis ◽

Juvenile Absence Epilepsy ◽

Generalized Epilepsy

Worsening of Seizures by Oxcarbazepine in Juvenile Idiopathic Generalized Epilepsies Gelisse P, Genton P, Kuate C, Pesenti A, Baldy-Moulinier M, Crespel A Epilepsia 2004;45:1282–1286 Purpose Several studies have shown that carbamazepine (CBZ) may aggravate idiopathic generalized epilepsy (IGE). Oxcarbazepine (OXC) is a new drug chemically related to CBZ. We report six cases of juvenile IGE with a clear aggravation by OXC. Methods We retrospectively studied all patients with IGE first referred to our epilepsy department between January 2001 and June 2003 and treated with OXC. Results During this period, six patients were identified. All had an aggravation of their epilepsy in both clinical and EEG activities. OXC had been used because of an incorrect diagnosis of focal epilepsy or generalized tonic–clonic seizures (GTCSs) of undetermined origin (no syndromic classification of the epilepsy). Before OXC, only one patient had experienced a worsening of seizures with an inadequate drug (carbamazepine; CBZ). Four had juvenile myoclonic epilepsy, one had juvenile absence epilepsy, and one had IGE that could not be classified into a precise syndrome. OXC (dosage range, 300–1,200 mg/day) was used in monotherapy in all of them except for one patient. Aggravation consisted of a clear aggravation of myoclonic jerks (five cases) or de novo myoclonic jerks (one case). Three patients had exacerbation of absence seizures. One patient had worsened dramatically and had absence status, and one had de novo absences after OXC treatment. The effects of OXC on GTCSs were less dramatic, with no worsening in frequency in three and a slight increase in three. Conclusions OXC can be added to the list of antiepileptic drugs that can exacerbate myoclonic and absence seizures in IGE.

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Absence of NEFL in patient-specific neurons in early-onset Charcot-Marie-Tooth neuropathy

Neurology Genetics ◽

10.1212/nxg.0000000000000244 ◽

2018 ◽

Vol 4 (3) ◽

pp. e244 ◽

Cited By ~ 8

Author(s):

Markus T. Sainio ◽

Emil Ylikallio ◽

Laura Mäenpää ◽

Jenni Lahtela ◽

Pirkko Mattila ◽

...

Keyword(s):

Nonsense Mutation ◽

Early Onset ◽

Messenger Rna ◽

Patient Specific ◽

Neuronal Cultures ◽

Cultured Neurons ◽

Loss Of Function ◽

Nonsense Mutations ◽

Neurofilament Light ◽

Charcot Marie Tooth

ObjectiveWe used patient-specific neuronal cultures to characterize the molecular genetic mechanism of recessive nonsense mutations in neurofilament light (NEFL) underlying early-onset Charcot-Marie-Tooth (CMT) disease.MethodsMotor neurons were differentiated from induced pluripotent stem cells of a patient with early-onset CMT carrying a novel homozygous nonsense mutation in NEFL. Quantitative PCR, protein analytics, immunocytochemistry, electron microscopy, and single-cell transcriptomics were used to investigate patient and control neurons.ResultsWe show that the recessive nonsense mutation causes a nearly total loss of NEFL messenger RNA (mRNA), leading to the complete absence of NEFL protein in patient's cultured neurons. Yet the cultured neurons were able to differentiate and form neuronal networks and neurofilaments. Single-neuron gene expression fingerprinting pinpointed NEFL as the most downregulated gene in the patient neurons and provided data of intermediate filament transcript abundancy and dynamics in cultured neurons. Blocking of nonsense-mediated decay partially rescued the loss of NEFL mRNA.ConclusionsThe strict neuronal specificity of neurofilament has hindered the mechanistic studies of recessive NEFL nonsense mutations. Here, we show that such mutation leads to the absence of NEFL, causing childhood-onset neuropathy through a loss-of-function mechanism. We propose that the neurofilament accumulation, a common feature of many neurodegenerative diseases, mimics the absence of NEFL seen in recessive CMT if aggregation prevents the proper localization of wild-type NEFL in neurons. Our results suggest that the removal of NEFL as a proposed treatment option is harmful in humans.

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A multi-modality approach to identifying primary generalized epilepsy that can mimic focal epilepsy

Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques ◽

10.1017/cjn.2015.114 ◽

2015 ◽

Vol 42 (S1) ◽

pp. S22-S22

Author(s):

BM Duaa ◽

A Ye ◽

S Doesburg ◽

H Otsubo ◽

A Ochi

Keyword(s):

Focal Epilepsy ◽

Final Diagnosis ◽

Absence Seizures ◽

Resective Surgery ◽

Group A ◽

Modality Approach ◽

Interictal Discharges ◽

Generalized Epilepsy ◽

Group B ◽

Video Eeg

Introduction: Evaluating the suitability for surgery in patients with epilepsy requires determining if the epilepsy is focal or generalized. Presurgical workups can indicate focal epilepsy in certain cases of generalized epilepsy (GE). The purpose of this study was to identify distinctive features which characterize patients with primary GE that mimics focal epilepsy. Method: We retrospectively identified 19 children with generalized interictal discharges during scalp video-EEG (SVEEG) and underwent invasive monitoring and/or epilepsy surgery. Two children did not undergo resective surgery due to final diagnosis of primary GE (Group A). Seventeen children underwent a resective surgery (Group B). Scalp video-EEG, MEG, MRI, and intracranial video EEG (IVEEG) were reviewed. Results: On (SVEEG), the frequency of generalized spike-and-waves (GSW) was 3Hz in Group A and 1.5-2.5Hz in Group B. Group A had only absence seizures , whereas 80% in Group B had multiple types of seizures. Both groups had lateralized MEG dipoles. One patient in Group A had a focal MRI abnormality. In Group A, IVEEG showed GSW of 3 Hz frequency with inconsistent leading. In Group B, IVEEG showed consistent localization of ictal and interictal high frequency oscillations. Conclusion: Children with generalized 3 Hz spike-and-waves and only absence seizures may be a contraindication of resective surgery even though some presurgical workup shows focality.

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Faculty Opinions recommendation of Early onset combined immunodeficiency and autoimmunity in patients with loss-of-function mutation in LAT.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.726389874.793520787 ◽

2016 ◽

Author(s):

Amnon Altman

Keyword(s):

Early Onset ◽

Combined Immunodeficiency ◽

Loss Of Function

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α-Synuclein-induced dysregulation of neuronal activity contributes to murine dopamine neuron vulnerability

npj Parkinson s Disease ◽

10.1038/s41531-021-00210-w ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Abeer Dagra ◽

Douglas R. Miller ◽

Min Lin ◽

Adithya Gopinath ◽

Fatemeh Shaerzadeh ◽

...

Keyword(s):

Parkinson’S Disease ◽

Parkinson's Disease ◽

Neuronal Activity ◽

Dopaminergic Neurons ◽

Prolonged Exposure ◽

D2 Receptor ◽

Neuronal Firing ◽

Dopamine Neurons ◽

Loss Of Function ◽

Therapeutic Implications

AbstractPathophysiological damages and loss of function of dopamine neurons precede their demise and contribute to the early phases of Parkinson’s disease. The presence of aberrant intracellular pathological inclusions of the protein α-synuclein within ventral midbrain dopaminergic neurons is one of the cardinal features of Parkinson’s disease. We employed molecular biology, electrophysiology, and live-cell imaging to investigate how excessive α-synuclein expression alters multiple characteristics of dopaminergic neuronal dynamics and dopamine transmission in cultured dopamine neurons conditionally expressing GCaMP6f. We found that overexpression of α-synuclein in mouse (male and female) dopaminergic neurons altered neuronal firing properties, calcium dynamics, dopamine release, protein expression, and morphology. Moreover, prolonged exposure to the D2 receptor agonist, quinpirole, rescues many of the alterations induced by α-synuclein overexpression. These studies demonstrate that α-synuclein dysregulation of neuronal activity contributes to the vulnerability of dopaminergic neurons and that modulation of D2 receptor activity can ameliorate the pathophysiology. These findings provide mechanistic insights into the insidious changes in dopaminergic neuronal activity and neuronal loss that characterize Parkinson’s disease progression with significant therapeutic implications.

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Early-Onset Osteoporosis

Calcified Tissue International ◽

10.1007/s00223-021-00885-6 ◽

2021 ◽

Author(s):

Outi Mäkitie ◽

M. Carola Zillikens

Keyword(s):

Young Adults ◽

Early Onset ◽

Type I Collagen ◽

Young Patients ◽

Fragility Fractures ◽

Underlying Disease ◽

Bone Fragility ◽

Sphingolipid Metabolism ◽

Type I ◽

Loss Of Function

AbstractOsteoporosis is a skeletal disorder with enhanced bone fragility, usually affecting the elderly. It is very rare in children and young adults and the definition is not only based on a low BMD (a Z-score < − 2.0 in growing children and a Z-score ≤ − 2.0 or a T-score ≤ − 2.5 in young adults) but also on the occurrence of fragility fractures and/or the existence of underlying chronic diseases or secondary factors such as use of glucocorticoids. In the absence of a known chronic disease, fragility fractures and low BMD should prompt extensive screening for secondary causes, which can be found in up to 90% of cases. When fragility fractures occur in childhood or young adulthood without an evident secondary cause, investigations should explore the possibility of an underlying monogenetic bone disease, where bone fragility is caused by a single variant in a gene that has a major role in the skeleton. Several monogenic forms relate to type I collagen, but other forms also exist. Loss-of-function variants in LRP5 and WNT1 may lead to early-onset osteoporosis. The X-chromosomal osteoporosis caused by PLS3 gene mutations affects especially males. Another recently discovered form relates to disturbed sphingolipid metabolism due to SGMS2 mutations, underscoring the complexity of molecular pathology in monogenic early-onset osteoporosis. Management of young patients consists of treatment of secondary factors, optimizing lifestyle factors including calcium and vitamin D and physical exercise. Treatment with bone-active medication should be discussed on a personalized basis, considering the severity of osteoporosis and underlying disease versus the absence of evidence on anti-fracture efficacy and potential harmful effects in pregnancy.

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The de novo CACNA1A pathogenic variant Y1384C associated with hemiplegic migraine, early onset cerebellar atrophy and developmental delay leads to a loss of Cav2.1 channel function

Molecular Brain ◽

10.1186/s13041-021-00745-2 ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Maria A. Gandini ◽

Ivana A. Souza ◽

Laurent Ferron ◽

A. Micheil Innes ◽

Gerald W. Zamponi

Keyword(s):

Developmental Delay ◽

Early Onset ◽

Structural Damage ◽

De Novo ◽

Splice Variants ◽

Cerebellar Atrophy ◽

Familial Hemiplegic Migraine ◽

Significant Loss ◽

Loss Of Function ◽

Hemiplegic Migraine

AbstractCACNA1A pathogenic variants have been linked to several neurological disorders including familial hemiplegic migraine and cerebellar conditions. More recently, de novo variants have been associated with severe early onset developmental encephalopathies. CACNA1A is highly expressed in the central nervous system and encodes the pore-forming CaVα1 subunit of P/Q-type (Cav2.1) calcium channels. We have previously identified a patient with a de novo missense mutation in CACNA1A (p.Y1384C), characterized by hemiplegic migraine, cerebellar atrophy and developmental delay. The mutation is located at the transmembrane S5 segment of the third domain. Functional analysis in two predominant splice variants of the neuronal Cav2.1 channel showed a significant loss of function in current density and changes in gating properties. Moreover, Y1384 variants exhibit differential splice variant-specific effects on recovery from inactivation. Finally, structural analysis revealed structural damage caused by the tyrosine substitution and changes in electrostatic potentials.

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Pathogenic STX3 variants affecting the retinal and intestinal transcripts cause an early-onset severe retinal dystrophy in microvillus inclusion disease subjects

Human Genetics ◽

10.1007/s00439-021-02284-1 ◽

2021 ◽

Author(s):

Andreas R. Janecke ◽

Xiaoqin Liu ◽

Rüdiger Adam ◽

Sumanth Punuru ◽

Arne Viestenz ◽

...

Keyword(s):

Early Onset ◽

Single Nucleotide Polymorphism Array ◽

Outer Nuclear Layer ◽

Retinal Dystrophy ◽

Geographic Origin ◽

Retinal Disease ◽

Homozygosity Mapping ◽

Rod Photoreceptor ◽

Loss Of Function ◽

Knockout Mouse Model

AbstractBiallelic STX3 variants were previously reported in five individuals with the severe congenital enteropathy, microvillus inclusion disease (MVID). Here, we provide a significant extension of the phenotypic spectrum caused by STX3 variants. We report ten individuals of diverse geographic origin with biallelic STX3 loss-of-function variants, identified through exome sequencing, single-nucleotide polymorphism array-based homozygosity mapping, and international collaboration. The evaluated individuals all presented with MVID. Eight individuals also displayed early-onset severe retinal dystrophy, i.e., syndromic—intestinal and retinal—disease. These individuals harbored STX3 variants that affected both the retinal and intestinal STX3 transcripts, whereas STX3 variants affected only the intestinal transcript in individuals with solitary MVID. That STX3 is essential for retinal photoreceptor survival was confirmed by the creation of a rod photoreceptor-specific STX3 knockout mouse model which revealed a time-dependent reduction in the number of rod photoreceptors, thinning of the outer nuclear layer, and the eventual loss of both rod and cone photoreceptors. Together, our results provide a link between STX3 loss-of-function variants and a human retinal dystrophy. Depending on the genomic site of a human loss-of-function STX3 variant, it can cause MVID, the novel intestinal-retinal syndrome reported here or, hypothetically, an isolated retinal dystrophy.

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