Genetic epileptic encephalopathies: is all written into the DNA?

Neuropsychological profiles of two patients with differing SCN8A-pathogenic variants

The impact of gene-related early infancy onset epilepsies in cognitive development can be potentially devastating. Here we report two cases of SCN8A-related epilepsy that highlight the neuropsychological heterogeneity seen with differing de-novo pathogenic variants. Case 1 is a 6-year-old right-handed girl who presented with SCN8A-developmental and epileptic encephalopathy (SCN8A-DEE) and a missense pathogenic variant (c.802A > C), not previously documented in the literature. Her history includes speech and motor delay, with focal motor seizures starting at 4-months. Early EEG showed bilateral centroparietal epileptiform discharges. She shows motor and language delays and prominent motor tics. Testing documented Intellectual Disability (ID) (Mild) with widespread neuropsychological deficits (i.e., academics, attention/executive functions, memory, visual-spatial skills, fine motor, language). Case 2 is an 8-year-old right-handed girl who presented with SCN8A-related epilepsy with c.5630A > G pathogenic variant with seizure onset at 5-months. Her initial EEG showed right occipital spikes. She shows low average intellect and average academics, but evaluation documented attention deficits, fine motor delays, and behavioral issues in addition to tics; she was diagnosed with Attention-Deficit/Hyperactivity Disorder, Oppositional Defiant Disorder, Obsessive Compulsive Disorder, and Tourette's. These cases expand limited knowledge regarding neuropsychological functioning of children with SCN8A-related epilepsy with unique de-novo pathogenic variants. While SCN8A-DEE is clearly associated with ID, other pathogenic variants may show better preserved intellect, despite other neuropsychological and behavioral concerns.

The epileptic and nonepileptic spectrum of paroxysmal dyskinesias: Channelopathies, synaptopathies, and transportopathies

Historically, the syndrome of primary paroxysmal dyskinesias was considered a group of disorders as a result of ion channel dysfunction. This proposition was primarily based on the discovery of mutations in ion channels, which caused other episodic neurological disorders such as epilepsy and migraine and also supported by the frequent association between paroxysmal dyskinesias and epilepsy. However, the discovery of the genes responsible for the 3 classic forms of paroxysmal dyskinesias disproved this ion channel theory. On the other hand, novel gene mutations implicating ion channels have been recently reported to produce episodic movement disorders clinically similar to the classic paroxysmal dyskinesias. Here, we review the clinical and pathophysiological aspects of the paroxysmal dyskinesias, further proposing a pathophysiological framework according to which they can be classified as synaptopathies (proline-rich transmembrane protein 2 and myofibrillogenesis regulator gene), channelopathies (calcium-activated potassium channel subunit alpha-1 and voltage-gated sodium channel type 8), or transportopathies (solute carrier family 2 member 1). This proposal might serve to explain similarities and differences among the various paroxysmal dyskinesias in terms of clinical features, treatment response, and natural history. © 2017 International Parkinson and Movement Disorder Society.

A Distinctive Ictal Amplitude-Integrated Electroencephalography Pattern in Newborns with Neonatal Epilepsy Associated with KCNQ2 Mutations

BACKGROUND

Recurrent and prolonged seizures are harmful for the developing brain, emphasizing the importance of early seizure recognition and effective therapy. Amplitude-integrated electroencephalography (aEEG) has become a valuable tool to diagnose epileptic seizures, and, in parallel, genetic etiologies are increasingly being recognized, changing the paradigm of the workup and management of neonatal seizures.

OBJECTIVE

To report the ictal aEEG pattern in neonates with KCNQ2-related epilepsy.

SUBJECTS AND METHODS

In this multicenter descriptive study, clinical data and aEEG findings of 9 newborns with KCNQ2 mutations are reported.

RESULTS

Refractory seizures occurred in the early neonatal period with similar seizure type, including tonic features, apnea, and desaturation. A distinct aEEG seizure pattern, consisting of a sudden rise of the lower and upper margin of the aEEG, followed by a marked depression of the aEEG amplitude, was found in 8 of the 9 patients. Prompt recognition of this pattern led to early treatment with carbamazepine in the 2 most recent cases.

CONCLUSION

Early recognition of the electroclinical phenotype by using aEEG may direct genetic testing and a precision medicine approach with sodium channel blockers in neonates with KCNQ2 mutations.

Autosomal dominant SCN8A mutation with an unusually mild phenotype

BACKGROUND

Mutations in SCN8A, coding for the voltage-gated sodium channel Nav 1.6, have been described in relation to infantile onset epilepsy with developmental delay and cognitive impairment, in particular early onset epileptic encephalopathy (EIEE) type 13.

CASE REPORT

Here we report an infant and his father with early onset focal epileptic seizures but without cognitive or neurological impairment in whom next generation sequence analysis identified a heterozygous mutation (c.5630A > G, p. (Asn1877Ser)) in the SCN8A gene. This mutation, confirmed by Sanger sequence analysis, affects a highly conserved amino acid and in silico tools predicts that it may be pathogenic. The reported infant has a normal developmental profile at 16-month follow-up. His father also had normal development and has no cognitive impairment at 42 years. This is the second known SCN8A mutation associated with a phenotype of benign familial infantile epilepsy. Good seizure control was achieved in our patients with sodium channel blockers.

CONCLUSION

Based on our proband and a recently described group of families with benign familial infantile epilepsy and SCN8A variant we suggest expanding testing to patients with infantile epilepsy and no cognitive impairment. In addition, the same SCN8A variant (c.5630A > G, p. (Asn1877Ser)) is also found in patients with epilepsy and developmental delay highlighting the phenotypic variability and the possible role of other protective genetic factors.

Serotonergic Modulation as Effective Treatment for Dravet Syndrome in a Zebrafish Mutant Model

Dravet syndrome (DS) is a severe epilepsy syndrome that starts within the first year of life. In a clinical study, add-on treatment with fenfluramine, a potent 5-hydroxytryptamine (5-HT) releaser activating multiple 5-HT receptor subtypes, made 70% of DS children seizure free. Others and we recently confirmed the efficacy of fenfluramine as an antiepileptiform compound in zebrafish models of DS. By using a large set of subtype selective agonists, in this study we examined which 5-HT receptor subtypes can be targeted to trigger antiseizure effects in homozygous scn1Lab(-/-) mutant zebrafish larvae that recapitulate DS well. We also provide evidence that zebrafish larvae express the orthologues of all human 5-HT receptor subtypes. Using an automated larval locomotor behavior assay, we were able to show that selective 5-HT1D-, 5-HT1E-, 5-HT2A-, 5-HT2C-, and 5-HT7-agonists significantly decreased epileptiform activity in the mutant zebrafish at 7 days post fertilization (dpf). By measuring local field potentials in the zebrafish larval forebrain, we confirmed the antiepileptiform activity of the 5-HT1D-, 5-HT2C-, and especially the 5-HT2A-agonist. Interestingly, we also found a significant decrease of serotonin in the heads of homozygous scn1Lab(-/-) mutants as compared to the wild type zebrafish, which suggest that neurochemical defects might play a crucial role in the pathophysiology of DS. Taken together, our results emphasize the high conservation of the serotonergic receptors in zebrafish larvae. Modulating certain serotonergic receptors was shown to effectively reduce seizures. Our findings therefore open new avenues for the development of future novel DS therapeutics.

PLCB1 epileptic encephalopathies; Review and expansion of the phenotypic spectrum

BACKGROUND

Biallelic loss-of-function mutations of phospholipase C-β1 (PLCB1) have been described in three children with an early onset epileptic encephalopathy (EE). In two of them a homozygous deletion of the promotor and first three coding exons was found. The third patient had an almost identical heterozygous deletion in combination with a heterozygous splice site variant. All patients had intractable epilepsy and a severe developmental delay.

METHODS AND RESULTS

We present the case of a boy with an infantile EE starting at the age of four months with a fever induced status epilepticus, modified hypsarrhythmia and developmental regression. The epilepsy was reasonably controlled with corticoids and valproate whereupon generalized tonic-clonic seizures appeared only each 3-4 months. However, only a slow developmental progress was seen hereafter, resulting in a severe intellectual disability with absent speech, motor delay and autistic features. We identified a novel homozygous partial deletion of PLCB1, affecting exons 7-9.

CONCLUSIONS

This report emphasizes the role of PLCB1 haploinsufficiency in severe EE. We demonstrate a phenotypic variability in patients with a PLCB1-associated EE. In addition, our findings underscore the importance of microarray analysis in all patients with an EE of unknown etiology.

Management of genetic epilepsies: From empirical treatment to precision medicine

Despite the over 20 antiepileptic drugs (AEDs) now licensed for epilepsy treatment, seizures can be effectively controlled in about ∼70% of patients. Thus, epilepsy treatment is still challenging in about one third of patients and this may lead to a severe medically, physically, and socially disabling condition. However, there is clear evidence of heterogeneity of response to existing AEDs and a significant unmet need for effective intervention. A number of studies have shown that polymorphisms may influence the poor or inadequate therapeutic response as well as the occurrence of adverse effects. In addition, the new frontier of genomic technologies, including chromosome microarrays and next-generation sequencing, improved our understanding of the genetic architecture of epilepsies. Recent findings in some genetic epilepsy syndromes provide insights into mechanisms of epileptogenesis, unrevealing the role of a number of genes with different functions, such as ion channels, proteins associated to the vesical synaptic cycle or involved in energy metabolism. The rapid progress of high-throughput genomic sequencing and corresponding analysis tools in molecular diagnosis are revolutionizing the practice and it is a fact that for some monogenic epilepsies the molecular confirmation may influence the choice of the treatment. Moreover, the novel genetic methods, that are able to analyze all known genes at a reasonable price, are of paramount importance to discover novel therapeutic avenues and individualized (or precision) medicine.

Genetics of reflex seizures and epilepsies in humans and animals

INTRODUCTION

Reflex seizures are epileptic events triggered by specific motor, sensory or cognitive stimulation. This comprehensive narrative review focuses on the role of genetic determinants in humans and animal models of reflex seizures and epilepsies.

METHODS

References were mainly identified through MEDLINE searches until August 2015 and backtracking of references in pertinent studies.

RESULTS

Autosomal dominant inheritance with reduced penetrance was proven in several families with photosensitivity. Molecular genetic studies on EEG photoparoxysmal response identified putative loci on chromosomes 6, 7, 13 and 16 that seem to correlate with peculiar seizure phenotype. No specific mutation has been found in Papio papio baboon, although a genetic etiology is likely. Mutation in synaptic vesicle glycoprotein 2A was found in another animal model of photosensitivity (Fayoumi chickens). Autosomal dominant inheritance with incomplete penetrance overlapping with a genetic background for IGE was proposed for some families with primary reading epilepsy. Musicogenic seizures usually occur in patients with focal symptomatic or cryptogenic epilepsies, but they have been reported in rare genetic epilepsies such as Dravet syndrome. A single LGI1 mutation has been described in a girl with seizures evoked by auditory stimuli. Interestingly, heterozygous knockout (Lgi1(+/-)) mice show susceptibility to sound-triggered seizures. Moreover, in Frings and Black Swiss mice, the spontaneous mutations of MASS1 and JAMS1 genes, respectively, have been linked to audiogenic seizures. Eating seizures usually occur in symptomatic epilepsies but evidences for a genetic susceptibility were mainly provided by family report from Sri Lanka. Eating seizures were also reported in rare patients with MECP2 duplication or mutation. Hot water seizures are genetically heterogeneous but two loci at chromosomes 4 and 10 were identified in families with likely autosomal dominant inheritance. Startle-induced seizures usually occur in patients with symptomatic epilepsies but have also been reported in the setting chromosomal disorders or genetically inherited lysosomal storage diseases.

DISCUSSION

The genetic background of reflex seizures and epilepsies is heterogeneous and mostly unknown with no major gene identified in humans. The benefits offered by next-generation sequencing technologies should be merged with increasing information on animal models that represent an useful tool to study the mechanism underlying epileptogenesis. Finally, we expect that genetic studies will lead to a better understanding of the multiple factors involved in the pathophysiology of reflex seizures, and eventually to develop preventive strategies focused on seizure control and therapy optimization.

Early-onset epileptic encephalopathy caused by gain-of-function mutations in the voltage sensor of Kv7.2 and Kv7.3 potassium channel subunits

Mutations in Kv7.2 (KCNQ2) and Kv7.3 (KCNQ3) genes, encoding for voltage-gated K(+) channel subunits underlying the neuronal M-current, have been associated with a wide spectrum of early-onset epileptic disorders ranging from benign familial neonatal seizures to severe epileptic encephalopathies. The aim of the present work has been to investigate the molecular mechanisms of channel dysfunction caused by voltage-sensing domain mutations in Kv7.2 (R144Q, R201C, and R201H) or Kv7.3 (R230C) recently found in patients with epileptic encephalopathies and/or intellectual disability. Electrophysiological studies in mammalian cells transfected with human Kv7.2 and/or Kv7.3 cDNAs revealed that each of these four mutations stabilized the activated state of the channel, thereby producing gain-of-function effects, which are opposite to the loss-of-function effects produced by previously found mutations. Multistate structural modeling revealed that the R201 residue in Kv7.2, corresponding to R230 in Kv7.3, stabilized the resting and nearby voltage-sensing domain states by forming an intricate network of electrostatic interactions with neighboring negatively charged residues, a result also confirmed by disulfide trapping experiments. Using a realistic model of a feedforward inhibitory microcircuit in the hippocampal CA1 region, an increased excitability of pyramidal neurons was found upon incorporation of the experimentally defined parameters for mutant M-current, suggesting that changes in network interactions rather than in intrinsic cell properties may be responsible for the neuronal hyperexcitability by these gain-of-function mutations. Together, the present results suggest that gain-of-function mutations in Kv7.2/3 currents may cause human epilepsy with a severe clinical course, thus revealing a previously unexplored level of complexity in disease pathogenetic mechanisms.

Clinical management of epileptic encephalopathies of childhood and infancy

Epileptic encephalopathies represent a group of devastating epileptic disorders that appear early in life and are characterized by pharmacoresistant generalized or focal seizures, persistent severe EEG abnormalities, and cognitive dysfunction or decline. The ictal and interictal epileptic discharges are age-specific and are either the main cause or contribute to cognitive deterioration in the idiopathic or symptomatic group respectively. Despite choosing the most appropriate anti-seizure drugs for the seizure-type and syndrome the results are often disappointing and polytherapy and/or alternative therapy becomes unavoidable. In those cases, consideration should be given to the quality of life of the child and carers. In this review we will discuss the clinical and EEG characteristics, evolution and management of age-related epileptic encephalopathies, recognized by the International League Against Epilepsy.