Multiplex families with epilepsy: Success of clinical and molecular genetic characterization

Developmental dysfunction in a preclinical model of Kcnq2 developmental and epileptic encephalopathy

BACKGROUND

Developmental and epileptic encephalopathies (DEE) are rare but severe neurodevelopmental disorders characterised by early-onset seizures often combined with developmental delay, behavioural and cognitive deficits. Treatment for DEEs is currently limited to seizure control and provides no benefits to the patients' developmental and cognitive outcomes. Genetic variants are the most common cause of DEE with KCNQ2 being one of the most frequently identified disease-causing genes. KCNQ2 encodes a voltage-gated potassium channel KV7.2 widely expressed in the central nervous system and critically involved in the regulation of neuronal excitability. In this study, we aimed to characterise a KCNQ2 variant (K556E) found in a female patient with DEE using a heterologous expression system and a knock-in mouse model.

METHODS

Wild-type KCNQ2 or K556E variant were expressed in Chinese Hamster Ovary (CHO) cells (with or without KCNQ3) and their biophysical properties assessed using patch clamp recordings. We further engineered a new Kcnq2 DEE mouse model (K557E) based on the K556E variant and characterised it using behavioural, electrophysiological, and transcriptome analysis.

RESULTS

A mild loss of function was observed only when the mutant channel was co-expressed with KCNQ3 in the heterologous system. The heterozygous knock-in mice showed a reduced survival rate and increased susceptibility to induced seizures. Electrophysiology recordings in brain slices revealed a hyperexcitable phenotype for cortical layer 2/3 pyramidal neurons with retigabine (KV7 channel opener) able to rescue both the increased sensitivity to chemically-induced seizures in vivo and neuronal excitability ex vivo. Whole-brain RNA sequencing revealed numerous differentially expressed genes and biological pathways pointing at dysregulation of early developmental processes.

CONCLUSIONS

Our study reports on a novel Kcnq2 DEE mouse model recapitulating aspects of the disease phenotype with the electrophysiological and transcriptome analysis providing insights into KCNQ2 DEE mechanisms that can be leveraged for future therapy development.

Novel LAMC3 pathogenic variant enriched in Finnish population causes malformations of cortical development and severe epilepsy

OBJECTIVE

Recessive LAMC3 mutations are recognized to cause epilepsy with cortical malformations characterized by polymicrogyria and pachygyria. The objective of this study was to describe the clinical picture and epilepsy phenotype of four patients with a previously undescribed LAMC3 variant.

METHODS

All epilepsy patients treated in Kuopio Epilepsy Center (located in Kuopio, Finland) are offered the possibility to participate in a scientific study investigating biomarkers in epilepsy (Epibiomarker study). We have collected a comprehensive database of the study population, and are currently re-evaluating our database regarding the patients with developmental and/or epileptic encephalopathy (DEE). If the etiology of epilepsy remains unknown in the clinical setting, we are performing whole exome sequencing to recognize the genetic causes.

RESULTS

Among our study population of 323 DEE patients we recognized three patients with similar homozygous LAMC3 c.1866del (p.(Phe623Serfs*10)) frameshift variant and one patient with a compound heterozygous mutation where the same frameshift variant was combined with an intronic LAMC3 c.4231-12C>G variant on another allele. All these patients have severe epilepsy and either bilateral agyria-pachygyria or bilateral polymicrogyria in their clinical MRI scanning. Cortical malformations involve the occipital lobes in all our patients. Epilepsy phenotype is variable as two of our patients have DEE with epileptic spasms progressing to Lennox-Gastaut syndrome and intellectual disability. The other two patients have focal epilepsy without marked cognitive deficit. The four patients are unrelated. LAMC3 c.1866del p.(Phe623Serfs*10) frameshift variant is enriched in the Finnish population.

SIGNIFICANCE

Only a few patients with epilepsy caused by LAMC3 homozygous or compound heterozygous mutations have been described in the literature. To our knowledge, the variants discovered in our patients have not previously been published. Clinical phenotype appears to be more varied than previously assumed and patients with a milder phenotype and normal cognition have probably remained unrecognized.

Case report: LAMC3-associated cortical malformations: Case report of a novel stop-gain variant and literature review

Background: Malformations of cortical development (MCDs) can lead to peculiar neuroradiological patterns and clinical presentations (i.e., seizures, cerebral palsy, and intellectual disability) according to the specific genetic pathway of the brain development involved; and yet a certain degree of phenotypic heterogeneity exists even when the same gene is affected. Here we report a man with an malformations of cortical development extending beyond occipital lobes associated with a novel stop-gain variant in LAMC3. Case presentation: The patient is a 28-year-old man suffering from drug-resistant epilepsy and moderate intellectual disability. He underwent a brain magnetic resonance imaging showing polymicrogyria involving occipital and temporal lobes bilaterally. After performing exome sequencing, a novel stop-gain variant in LAMC3 (c.3871C>T; p. Arg1291*) was identified. According to the cortical alteration of the temporal regions, temporal seizures were detected; instead, the patient did not report occipital seizures. Different pharmacological and non-pharmacological interventions (i.e., vagus nerve stimulation) were unsuccessful, even though a partial seizure reduction was obtained after cenobamate administration. Conclusion: Our case report confirms that variants of a gene known to be related to specific clinical and neuroradiological pictures can unexpectedly lead to new phenotypes involving different areas of the brain.

A New Case With Cortical Malformation Caused by Biallelic Variants in LAMC3

Objective

In this study, we report the case of a 24-year-old man with intellectual disability and childhood-onset seizures. This patient had newly identified biallelic variants in the laminin subunit gamma 3 (LAMC3) gene with unreported cortical malformation.

Methods

Exome sequencing.

Results

Genetic analyses revealed new biallelic variants in the LAMC3 gene. An MRI examination of the brain revealed cortical malformations predominantly in the temporal lobes and mildly in the occipital, frontal, and parietal lobes. In addition, our patient also exhibited mild midline malformation in the ventral pons, which is unique to LAMC3 variants.

Discussion

Patients with LAMC3 variants have been reported to exhibit cortical malformation predominantly in the occipital lobes, but this patient exhibited cortical malformation predominantly in the temporal lobes and mildly in the occipital, frontal, and parietal lobes. In addition, this patient also exhibited mild midline malformation in the ventral pons. These unique findings cast new light on the role of LAMC3 in brain development.

CB2R induces a protective response against epileptic seizures through ERK and p38 signaling pathways

BACKGROUND AND PURPOSE

Epilepsy is a pivotal neurological disorder characterized by the synchronous discharging of neurons to induce momentary brain dysfunction. Temporal lobe epilepsy is the most common type of epilepsy, with seizures originating from the mesial temporal lobe. The hippocampus forms part of the mesial temporal lobe and plays a significant role in epileptogenesis; it also has a vital influence on the mental development of children. In this study, we aimed to explore the effects of CB2 receptor (CB2R) activation on ERK and p38 signaling in nerve cells of a rat epilepsy model.

MATERIALS AND METHODS

We treated Sprague-Dawley rats with pilocarpine to induce an epilepsy model and treated such animals with a CB2R agonist (JWH133) alone or with a CB2R antagonist (AM630). Nissl's stain showed the neuron conditon in different groups. Western blot analyzed the level of p-ERK and p-p38.

RESULTS

JWH133 can increase the latent period of first seizure attack and decrease the Grades IV-V magnitude ratio after the termination of SE. Nissl's stain showed JWH133 protected neurons in the hippocampus while AM630 inhibited the functioning of CB2R in neurons. Western blot analysis showed that JWH133 decreased levels of p-ERK and p-p38, which is found at increased levels in the hippocampus of our epilepsy model. In contrast, AM630 inhibited the protective function of JWH133 and also enhanced levels of p-ERK and p-p38.

CONCLUSIONS

CB2R activation can induce neurons proliferation and survival through activation of ERK and p38 signaling pathways.

Variants in LAMC3 Causes Occipital Cortical Malformation

Occipital cortical malformation (OCCM) is a disease caused by malformations of cortical development characterized by polymicrogyria and pachygyria of the occipital lobes and childhood-onset seizures. The recessive or complex heterozygous variants of the LAMC3 gene are identified as the cause of OCCM. In the present study, we identified novel complex heterozygous variants (c.470G > A and c.4030 + 1G > A) of the LAMC3 gene in a Chinese female with childhood-onset seizures. Cranial magnetic resonance imaging was normal. Functional experiments confirmed that both variant sites caused premature truncation of the laminin γ3 chain. Bioinformatics analysis predicted 10 genes interacted with LAMC3 with an interaction score of 0.4 (P value = 1.0e–16). The proteins encoded by these genes were mainly located in the basement membrane and extracellular matrix component. Furthermore, the biological processes and molecular functions from gene ontology analysis indicated that laminin γ3 chain and related proteins played an important role in structural support and cellular processes through protein-containing complex binding and signaling receptor binding. KEGG pathway enrichment predicted that the LAMC3 gene variant was most likely to participate in the occurrence and development of OCCM through extracellular matrix receptor interaction and PI3K-Akt signaling pathway.

Dravet syndrome and Dravet syndrome-like phenotype: a systematic review of the SCN1A and PCDH19 variants

Dravet syndrome (DS) is a rare and severe epileptic syndrome of childhood with prevalence between 1/22,000 and 1/49,900 of live births. Approximately 80% of patients with this syndrome present SCN1A pathogenic variants, which encodes an alpha subunit of a neural voltage-dependent sodium channel. There is a correlation between PCDH19 pathogenic variants, encodes the protocadherin 19, and a similar disease to DS known as DS-like phenotype. The present review aims to clarify the differences between DS and DS-like phenotype according to the SCN1A and PCDH19 variants. A systematic review was conducted in PubMed and Virtual Health Library (VHL) databases, using "Dravet Syndrome" and "Severe Myoclonic Epilepsy in Infancy (SMEI)" search words, selecting cohort of studies published in journal with impact factor of two or greater. The systematic review was according to the Preferred Reporting Items for Systematic Review and Meta-Analysis recommendations. Nineteen studies were included in the present review, and a significant proportion of patients with DS-carrying SCN1A was greater than patients with DS-like phenotype-harboring PCDH19 variants (76.6% versus 23.4%). When clinical and genetic data were correlated, autism was predominantly observed in patients with DS-like-carrying PCDH19 variants compared to SCN1A variant carriers (62.5% versus 37.5%, respectively, P-value = 0.044, P-value corrected = 0.198). In addition, it was noticed a significant predisposition to hyperthermia during epilepsy crisis in individuals carrying PCDH19 variants (P-value = 0.003; P-value corrected = 0.027). The present review is the first to point out differences between the DS and DS-like phenotype according to the SCN1A and PCDH19 variants.

Compound heterozygous variants in LAMC3 in association with posterior periventricular nodular heterotopia

BACKGROUND

Periventricular nodular heterotopia (PNH) is a malformation of cortical development characterized by nodules of abnormally migrated neurons. The cause of posteriorly placed PNH is not well characterised and we present a case that provides insights into the cause of posterior PNH.

CASE PRESENTATION

We report a fetus with extensive posterior PNH in association with biallelic variants in LAMC3. LAMC3 mutations have previously been shown to cause polymicrogyria and pachygyria in the occipital cortex, but not PNH. The occipital location of PNH in our case and the proposed function of LAMC3 in cortical development suggest that the identified LAMC3 variants may be causal of PNH in this fetus.

CONCLUSION

We hypothesise that this finding extends the cortical phenotype associated with LAMC3 and provides valuable insight into genetic cause of posterior PNH.

Dyshomeostatic modulation of Ca2+-activated K+ channels in a human neuronal model of KCNQ2 encephalopathy

Mutations in KCNQ2, which encodes a pore-forming K⁺ channel subunit responsible for neuronal M-current, cause neonatal epileptic encephalopathy, a complex disorder presenting with severe early-onset seizures and impaired neurodevelopment. The condition is exceptionally difficult to treat, partially because the effects of KCNQ2 mutations on the development and function of human neurons are unknown. Here, we used induced pluripotent stem cells (iPSCs) and gene editing to establish a disease model and measured the functional properties of differentiated excitatory neurons. We find that patient iPSC-derived neurons exhibit faster action potential repolarization, larger post-burst afterhyperpolarization and a functional enhancement of Ca²⁺-activated K⁺ channels. These properties, which can be recapitulated by chronic inhibition of M-current in control neurons, facilitate a burst-suppression firing pattern that is reminiscent of the interictal electroencephalography pattern in patients. Our findings suggest that dyshomeostatic mechanisms compound KCNQ2 loss-of-function leading to alterations in the neurodevelopmental trajectory of patient iPSC-derived neurons.

Epilepsy risk in offspring of affected parents; a cohort study of the "maternal effect" in epilepsy

OBJECTIVE

To assess whether the risk of epilepsy is higher in offspring of mothers with epilepsy than in offspring of fathers with epilepsy.

METHODS

In a prospective population-based register study, we considered all singletons born in Denmark between 1981 and 2016 (N = 1,754,742). From the Danish National Patient Register since 1977, we identified epilepsy diagnoses in all study participants and their family members. Cox regression models were used to estimate hazard ratios (HRs) and corresponding 95% confidence intervals (CI), adjusted for relevant confounders.

RESULTS

We included 1,754,742 individuals contributing > 30 million person-years of follow-up. The incidence rate of epilepsy in offspring of unaffected parents was 78.8 (95% CI: 77.8-79.8) per 100,000 person-years, while the corresponding rate in offspring with an affected father was 172 per 100,000 person-years (95% CI: 156-187) and in offspring with an affected mother was 260 per 100,000 person-years (95% CI: 243-277). Having an affected mother was associated with a 1.45-fold (95% CI: 1.30-1.63) higher risk of epilepsy in the offspring, compared to having an affected father. This maternal effect was found both in male (HR = 1.39, 95% CI: 1.19-1.62) and female offspring (HR = 1.53, 95% CI: 1.30-1.80), and across various ages at onset in the offspring. The maternal effect was also found in familial epilepsies (i.e. where the affected parent had an affected sibling; HR = 1.50, 95% CI: 1.04-2.16).

INTERPRETATION

We found a clear maternal effect on offspring risk of epilepsy in this nationwide cohort study.

A novel splice variant expands the LAMC3-associated cortical phenotype to frontal only polymicrogyria and adult-onset epilepsy

Bi-allelic loss-of-function variants in LAMC3, encoding extracellular matrix protein laminin gamma 3, represent a rare cause of occipital polymicrogyria with epilepsy, developmental delay and cognitive impairment. So far, only five families have been reported. We now identified a novel, homozygous splice variant in LAMC3 in an individual with an unusual manifestation of cortical malformation. She presented with polymicrogyria in the frontal but not the occipital lobes, with adult-onset seizures and normal psychomotor development and cognition. Additionally, ictal asystole, requiring implantation of a pacemaker, and nonepileptic seizures occurred. This case expands the spectrum of LAMC3-associated cortical malformation phenotypes to frontal only polymicrogyria and adult-onset of epilepsy.

The "maternal effect" on epilepsy risk: Analysis of familial epilepsies and reassessment of prior evidence

OBJECTIVE

Previous studies have observed that epilepsy risk is higher among offspring of affected women than offspring of affected men. We tested whether this "maternal effect" was present in familial epilepsies, which are enriched for genetic factors that contribute to epilepsy risk.

METHODS

We assessed evidence of a maternal effect in a cohort of families containing ≥3 persons with epilepsy using 3 methods: (1) "downward-looking" analysis, comparing the rate of epilepsy in offspring of affected women versus men; (2) "upward-looking" analysis, comparing the rate of epilepsy among mothers versus fathers of affected individuals; and (3) lineage analysis, comparing the proportion of affected individuals with family history of epilepsy on the maternal versus paternal side.

RESULTS

Downward-looking analysis revealed no difference in epilepsy rates among offspring of affected mothers versus fathers (prevalence ratio = 1.0, 95% confidence interval [CI] = 0.8-1.2). Upward-looking analysis revealed more affected mothers than affected fathers; this effect was similar for affected and unaffected sibships (odds ratio = 0.8, 95% CI = 0.5-1.2) and was explained by a combination of differential fertility and participation rates. Lineage analysis revealed no significant difference in the likelihood of maternal versus paternal family history of epilepsy.

INTERPRETATION

We found no evidence of a maternal effect on epilepsy risk in this familial epilepsy cohort. Confounding sex imbalances can create the appearance of a maternal effect in upward-looking analyses and may have impacted prior studies. We discuss possible explanations for the lack of evidence, in familial epilepsies, of the maternal effect observed in population-based studies. ANN NEUROL 2020;87:132-138.

Unverricht-Lundborg disease: Clinical course and seizure management based on the experience of polish centers

The purpose of this paper was to present our experience following the longterm treatment of 11 patients with Unverricht-Lundborg disease (ULD) confirmed by molecular testing.

METHODS

We analyzed the clinical course, cognitive state, neuroimaging and neurophysiology results.

RESULTS

The data were collected from 9 unrelated families (F/M: 4/7) aged 25-49. The most frequent early manifestations of ULD include generalized tonic-clonic seizures (GTCS) accompanied by myoclonus 2 years later. Myoclonus was observed in all of the patients; its severity made it impossible for 91% to move independently. In two patients- mild atrophy of brain were observed in the MRI. More than half of the patients who underwent evoked potential presented no abnormalities. The dominant EEG-change was slow background activity in all of the patients. Seven patients had generalized seizure activity. The patients received antiepileptic therapy modifications depending on the severity of symptoms and stage of the disease. Five patients received N-acetyl-cysteine.

CONCLUSIONS

ULD patients require anti-epileptic polytherapy, mostly benefitting from managing GTCS and myoclonus with valproic acid and clonazepam treatment. Patients may benefit from add-on therapy with levetiracetam or topiramate. An increase in myoclonus, resulting from the progressive nature of the disease leads to significant disability in the majority of patients.

CB2R induces a protective response for epileptic seizure via the PI3K 110α-AKT signaling pathway

Epilepsy is a chronic brain disease caused by abnormal discharging in the brain, which induces momentary brain dysfunction. Cannabinoid 2 receptor (CB2R) is expressed in central nervous system (CNS) and serves an important role in the pathogenesis of CNS diseases. The aim of the present study was to explore the effects of CB2R activation on phosphoinositide 3-kinase (PI3K) 110α-protein kinase B (AKT) signaling in an astrocyte model of epilepsy. Rat CTX TNA2 astrocytes were treated with Mg free solution to establish a cell model of epilepsy and were subsequently treated with a CB2R agonist (JWH133) and antagonist (AM630). Cell cycle analysis revealed that treatment using Mg free solution inhibited cell cycle transition. JWH133 facilitated cell cycle progression while AM630 inhibited it. Western blotting results demonstrated that treatment with Mg free solution downregulated the expression of cyclin D1, cyclin E, phosphorylated Retinoblastoma (p-Rb), B-cell lymphoma 2 (Bcl-2), PI3K 110α, p-AKT and p-mammalian target of rapamycin, whereas JWH133 treatment upregulated these proteins. AM630 ameliorated the JWH133-induced upregulation of these proteins. To confirm the involvement of AKT signaling, the AKT inhibitor wortmannin was used. The results revealed that wortmannin inhibited the effect of JWH133 on p-AKT, cyclin D1, p-Rb and Bcl-2 expression. In addition, the effects of JWH133 and AM630 on PI3K 110α-AKT signaling were verified using a rat model of epilepsy. In conclusion, the present study demonstrates that CB2R activation induces astrocyte proliferation and survival via activation of the PI3K 110α-AKT signaling pathway.

Rare gene deletions in genetic generalized and Rolandic epilepsies

Genetic Generalized Epilepsy (GGE) and benign epilepsy with centro-temporal spikes or Rolandic Epilepsy (RE) are common forms of genetic epilepsies. Rare copy number variants have been recognized as important risk factors in brain disorders. We performed a systematic survey of rare deletions affecting protein-coding genes derived from exome data of patients with common forms of genetic epilepsies. We analysed exomes from 390 European patients (196 GGE and 194 RE) and 572 population controls to identify low-frequency genic deletions. We found that 75 (32 GGE and 43 RE) patients out of 390, i.e. ~19%, carried rare genic deletions. In particular, large deletions (>400 kb) represent a higher burden in both GGE and RE syndromes as compared to controls. The detected low-frequency deletions (1) share genes with brain-expressed exons that are under negative selection, (2) overlap with known autism and epilepsy-associated candidate genes, (3) are enriched for CNV intolerant genes recorded by the Exome Aggregation Consortium (ExAC) and (4) coincide with likely disruptive de novo mutations from the NPdenovo database. Employing several knowledge databases, we discuss the most prominent epilepsy candidate genes and their protein-protein networks for GGE and RE.

Potassium Channel Gain of Function in Epilepsy: An Unresolved Paradox

Exome and targeted sequencing have revolutionized clinical diagnosis. This has been particularly striking in epilepsy and neurodevelopmental disorders, for which new genes or new variants of preexisting candidate genes are being continuously identified at increasing rates every year. A surprising finding of these efforts is the recognition that gain of function potassium channel variants are actually associated with certain types of epilepsy, such as malignant migrating partial seizures of infancy or early-onset epileptic encephalopathy. This development has been difficult to understand as traditionally potassium channel loss-of-function, not gain-of-function, has been associated with hyperexcitability disorders. In this article, we describe the current state of the field regarding the gain-of-function potassium channel variants associated with epilepsy (KCNA2, KCNB1, KCND2, KCNH1, KCNH5, KCNJ10, KCNMA1, KCNQ2, KCNQ3, and KCNT1) and speculate on the possible cellular mechanisms behind the development of seizures and epilepsy in these patients. Understanding how potassium channel gain-of-function leads to epilepsy will provide new insights into the inner working of neural circuits and aid in developing new therapies.

Genetic epilepsy with febrile seizures plus: Refining the spectrum

OBJECTIVE

Following our original description of generalized epilepsy with febrile seizures plus (GEFS+) in 1997, we analyze the phenotypic spectrum in 409 affected individuals in 60 families (31 new families) and expand the GEFS+ spectrum.

METHODS

We performed detailed electroclinical phenotyping on all available affected family members. Genetic analysis of known GEFS+ genes was carried out where possible. We compared our phenotypic and genetic data to those published in the literature over the last 19 years.

RESULTS

We identified new phenotypes within the GEFS+ spectrum: focal seizures without preceding febrile seizures (16/409 [4%]), classic genetic generalized epilepsies (22/409 [5%]), and afebrile generalized tonic-clonic seizures (9/409 [2%]). Febrile seizures remains the most frequent phenotype in GEFS+ (178/409 [44%]), followed by febrile seizures plus (111/409 [27%]). One third (50/163 [31%]) of GEFS+ families tested have a pathogenic variant in a known GEFS+ gene.

CONCLUSION

As 37/409 (9%) affected individuals have focal epilepsies, we suggest that GEFS+ be renamed genetic epilepsy with febrile seizures plus rather than generalized epilepsy with febrile seizures plus. The phenotypic overlap between GEFS+ and the classic generalized epilepsies is considerably greater than first thought. The clinical and molecular data suggest that the 2 major groups of generalized epilepsies share genetic determinants.

Phenotypic analysis of 303 multiplex families with common epilepsies

Gene identification in epilepsy has mainly been limited to large families segregating genes of major effect and de novo mutations in epileptic encephalopathies. Many families that present with common non-acquired focal epilepsies and genetic generalized epilepsies remain unexplained. We assembled a cohort of 'genetically enriched' common epilepsies by collecting and phenotyping families containing multiple individuals with unprovoked seizures. We aimed to determine if specific clinical epilepsy features aggregate within families, and whether this segregation of phenotypes may constitute distinct 'familial syndromes' that could inform genomic analyses. Families with three or more individuals with unprovoked seizures were studied across multiple international centres. Affected individuals were phenotyped and classified according to specific electroclinical syndromes. Families were categorized based on syndromic groupings of affected family members, examined for pedigree structure and phenotypic patterns and, where possible, assigned specific familial epilepsy syndromes. A total of 303 families were assembled and analysed, comprising 1120 affected phenotyped individuals. Of the 303 families, 117 exclusively segregated generalized epilepsy, 62 focal epilepsy, and 22 were classified as genetic epilepsy with febrile seizures plus. Over one-third (102 families) were observed to have mixed epilepsy phenotypes: 78 had both generalized and focal epilepsy features within the same individual (n = 39), or within first or second degree relatives (n = 39). Among the genetic generalized epilepsy families, absence epilepsies were found to cluster within families independently of juvenile myoclonic epilepsy, and significantly more females were affected than males. Of the 62 familial focal epilepsy families, two previously undescribed familial focal syndrome patterns were evident: 15 families had posterior quadrant epilepsies, including seven with occipito-temporal localization and seven with temporo-parietal foci, and four families displayed familial focal epilepsy of childhood with multiple affected siblings that was suggestive of recessive inheritance. The findings suggest (i) specific patterns of syndromic familial aggregation occur, including newly recognized forms of familial focal epilepsy; (ii) although syndrome-specificity usually occurs in multiplex families, the one-third of families with features of both focal and generalized epilepsy is suggestive of shared genetic determinants; and (iii) patterns of features observed across families including pedigree structure, sex, and age of onset may hold clues for future gene identification. Such detailed phenotypic information will be invaluable in the conditioning and interpretation of forthcoming sequencing data to understand the genetic architecture and inter-relationships of the common epilepsy syndromes.

Myoclonus epilepsy and ataxia due to KCNC1 mutation: Analysis of 20 cases and K+ channel properties

OBJECTIVE

To comprehensively describe the new syndrome of myoclonus epilepsy and ataxia due to potassium channel mutation (MEAK), including cellular electrophysiological characterization of observed clinical improvement with fever.

METHODS

We analyzed clinical, electroclinical, and neuroimaging data for 20 patients with MEAK due to recurrent KCNC1 p.R320H mutation. In vitro electrophysiological studies were conducted using whole cell patch-clamp to explore biophysical properties of wild-type and mutant K_V 3.1 channels.

RESULTS

Symptoms began at between 3 and 15 years of age (median = 9.5), with progressively severe myoclonus and rare tonic-clonic seizures. Ataxia was present early, but quickly became overshadowed by myoclonus; 10 patients were wheelchair-bound by their late teenage years. Mild cognitive decline occurred in half. Early death was not observed. Electroencephalogram (EEG) showed generalized spike and polyspike wave discharges, with documented photosensitivity in most. Polygraphic EEG-electromyographic studies demonstrated a cortical origin for myoclonus and striking coactivation of agonist and antagonist muscles. Magnetic resonance imaging revealed symmetrical cerebellar atrophy, which appeared progressive, and a prominent corpus callosum. Unexpectedly, transient clinical improvement with fever was noted in 6 patients. To explore this, we performed high-temperature in vitro recordings. At elevated temperatures, there was a robust leftward shift in activation of wild-type K_V 3.1, increasing channel availability.

INTERPRETATION

MEAK has a relatively homogeneous presentation, resembling Unverricht-Lundborg disease, despite the genetic and biological basis being quite different. A remarkable improvement with fever may be explained by the temperature-dependent leftward shift in activation of wild-type K_V 3.1 subunit-containing channels, which would counter the loss of function observed for mutant channels, highlighting KCNC1 as a potential target for precision therapeutics. Ann Neurol 2017;81:677-689.

Variable expressivity of a likely pathogenic variant in KCNQ2 in a three-generation pedigree presenting with intellectual disability with childhood onset seizures

KCNQ2 has been reported as a frequent cause of autosomal dominant benign familial neonatal seizures. De novo likely pathogenic variants in KCNQ2 have been described in neonatal or early infantile onset epileptic encephalopathy patients. Here, we report a three-generation family with six affected patients with a novel likely pathogenic variant (c.628C>T; p.Arg210Cys) in KCNQ2. Four family members, three adults and a child, presented with a childhood seizure onset with variability in the severity of seizures and response to treatment, intellectual disability (ID) as well as behavioral problems. The two youngest affected patients had a variable degree of global developmental delay with no seizures at their current age. This three-generation family with six affected members expands the phenotypic spectrum of KCNQ2 associated encephalopathy to KCNQ2 associated ID and or childhood onset epileptic encephalopathy. We think that KCNQ2 associated epileptic encephalopathy should be included in the differential diagnosis of childhood onset epilepsy and early onset global developmental delay, cognitive dysfunction, or ID. Furthermore, whole exome sequencing in families with ID and history of autosomal dominant inheritance pattern with or without seizures, may further broaden the phenotypic spectrum of KCNQ2 associated epileptic encephalopathy or encephalopathy.