FHF1 (FGF12) epileptic encephalopathy

Loss of Intracellular Fibroblast Growth Factor 14 (iFGF14) Increases the Excitability of Mature Hippocampal and Cortical Pyramidal Neurons

Mutations in FGF14 , which encodes intracellular fibroblast growth factor 14 (iFGF14), have been linked to spinocerebellar ataxia type 27 (SCA27), a multisystem disorder associated with progressive deficits in motor coordination and cognitive function. Mice ( Fgf14 -/- ) lacking iFGF14 display similar phenotypes, and we have previously shown that the deficits in motor coordination reflect reduced excitability of cerebellar Purkinje neurons, owing to the loss of iFGF14-mediated regulation of the voltage-dependence of inactivation of the fast transient component of the voltage-gated Na + (Nav) current, I NaT . Here, we present the results of experiments designed to test the hypothesis that loss of iFGF14 also attenuates the intrinsic excitability of mature hippocampal and cortical pyramidal neurons. Current-clamp recordings from adult mouse hippocampal CA1 pyramidal neurons in acute in vitro slices, however, revealed that repetitive firing rates were higher in Fgf14 -/- , than in wild type (WT), cells. In addition, the waveforms of individual action potentials were altered in Fgf14 -/- hippocampal CA1 pyramidal neurons, and the loss of iFGF14 reduced the time delay between the initiation of axonal and somal action potentials. Voltage-clamp recordings revealed that the loss of iFGF14 altered the voltage-dependence of activation, but not inactivation, of I NaT in CA1 pyramidal neurons. Similar effects of the loss of iFGF14 on firing properties were evident in current-clamp recordings from layer 5 visual cortical pyramidal neurons. Additional experiments demonstrated that the loss of iFGF14 does not alter the distribution of anti-Nav1.6 or anti-ankyrin G immunofluorescence labeling intensity along the axon initial segments (AIS) of mature hippocampal CA1 or layer 5 visual cortical pyramidal neurons in situ . Taken together, the results demonstrate that, in contrast with results reported for neonatal (rat) hippocampal pyramidal neurons in dissociated cell culture, the loss of iFGF14 does not disrupt AIS architecture or Nav1.6 localization/distribution along the AIS of mature hippocampal (or cortical) pyramidal neurons in situ .

Early-Onset Epileptic Encephalopathy Responsive to Phenytoin: A Diagnostic Clue for Fibroblast Growth Factor 12 Mutation

We present a case of a three-year-old girl with a rare genetic epilepsy with developmental delay. She was born to a non-consanguineous parentage and required resuscitation soon after delivery via cesarean section. The patient had her first seizure within 36 hours of life, which progressed into refractory epilepsy. She required multiple hospital admissions due to prolonged seizures. Despite being tried on multiple drug combinations over the years, she responded only to phenytoin. Basic imaging and other investigations, including genetic analysis, revealed a fibroblast growth factor 12 (FGF12) mutation. Mutations in these genes cause refractory early-onset seizures associated with severe developmental delay. Due to early and appropriate intervention with phenytoin, she had good seizure control which probably resulted in a better developmental outcome.

FGF12: biology and function

Fibroblast growth factor 12 (FGF12) belongs to the fibroblast growth factor homologous factors (FHF) subfamily, which is also known as the FGF11 subfamily. The human FGF12 gene is located on chromosome 3 and consists of four introns and five coding exons. Their alternative splicing results in two FGF12 isoforms - the shorter 'b' isoform and the longer 'a' isoform. Structurally, the core domain of FGF12, is highly homologous to that of the other FGF proteins, providing the classical tertiary structure of β-trefoil. FGF12 is expressed in various tissues, most abundantly in excitable cells such as neurons and cardiomyocytes. For many years, FGF12 was thought to be exclusively an intracellular protein, but recent studies have shown that it can be secreted despite the absence of a canonical signal for secretion. The best-studied function of FGF12 relates to its interaction with sodium channels. In addition, FGF12 forms complexes with signaling proteins, regulates the cytoskeletal system, binds to the FGF receptors activating signaling cascades to prevent apoptosis and interacts with the ribosome biogenesis complex. Importantly, FGF12 has been linked to nervous system disorders, cancers and cardiac diseases such as epileptic encephalopathy, pulmonary hypertension and cardiac arrhythmias, making it a potential target for gene therapy as well as a therapeutic agent.

FGF12 is a novel component of the nucleolar NOLC1/TCOF1 ribosome biogenesis complex

Among the FGF proteins, the least characterized superfamily is the group of fibroblast growth factor homologous factors (FHFs). To date, the main role of FHFs has been primarily seen in the modulation of voltage-gated ion channels, but a full picture of the function of FHFs inside the cell is far from complete. In the present study, we focused on identifying novel FGF12 binding partners to indicate its intracellular functions. Among the identified proteins, a significant number were nuclear proteins, especially RNA-binding proteins involved in translational processes, such as ribosomal processing and modification. We have demonstrated that FGF12 is localized to the nucleolus, where it interacts with NOLC1 and TCOF1, proteins involved in the assembly of functional ribosomes. Interactions with both NOLC1 and TCOF1 are unique to FGF12, as other FHF proteins only bind to TCOF1. The formation of nucleolar FGF12 complexes with NOLC1 and TCOF1 is phosphorylation-dependent and requires the C-terminal region of FGF12. Surprisingly, NOLC1 and TCOF1 are unable to interact with each other in the absence of FGF12. Taken together, our data link FHF proteins to nucleoli for the first time and suggest a novel and unexpected role for FGF12 in ribosome biogenesis. Video Abstract.

Fibroblast growth factor homologous factor 2 attenuates excitability of DRG neurons

Fibroblast growth factor homologous factors (FHFs) are cytosolic members of the superfamily of the FGF proteins. Four members of this subfamily (FHF1-4) are differentially expressed in multiple tissues in an isoform-dependent manner. Mutations in FHF proteins have been associated with multiple neurological disorders. FHF proteins bind to the COOH terminus of voltage-gated sodium (Nav) channels and regulate current amplitude and gating properties of these channels. FHF2, which is expressed in dorsal root ganglia (DRG) neurons, has two main splicing isoforms: FHF2A and FHF2B, which differ in the length and sequence of their NH₂ termini, have been shown to differentially regulate gating properties of Nav1.7, a channel that is a major driver of DRG neuron firing. FHF2 expression levels are downregulated after peripheral nerve axotomy, which suggests that they may regulate neuronal excitability via an action on Nav channels after injury. We have previously shown that knockdown of FHF2 leads to gain-of-function changes in Nav1.7 gating properties: enhanced repriming, increased current density, and hyperpolarized activation. From this we posited that knockdown of FHF2 might also lead to DRG hyperexcitability. Here we show that knockdown of either FHF2A alone or all isoforms of FHF2 results in increased DRG neuron excitability. In addition, we demonstrate that supplementation of FHF2A and FHF2B reduces DRG neuron excitability. Overexpression of FHF2A or FHF2B also reduced excitability of DRG neurons treated with a cocktail of inflammatory mediators, a model of inflammatory pain. Our data suggest that increased neuronal excitability after nerve injury might be triggered, in part, via a loss of FHF2-Nav1.7 interaction.NEW & NOTEWORTHY FHF2 is known to bind to and modulate the function of Nav1.7. FHF2 expression is also reduced after nerve injury. We demonstrate that knockdown of FHF2 expression increases DRG neuronal excitability. More importantly, overexpression of FHF2 reduces DRG excitability in basal conditions and in the presence of inflammatory mediators (a model of inflammatory pain). These results suggest that FHF2 could potentially be used as a tool to reduce DRG neuronal excitability and to treat pain.

Differential regulation of gene expression pathways with dexamethasone and ACTH after early life seizures

Early-life seizures (ELS) are associated with persistent cognitive deficits such as ADHD and memory impairment. These co-morbidities have a dramatic negative impact on the quality of life of patients. Therapies that improve cognitive outcomes have enormous potential to improve patients' quality of life. Our previous work in a rat flurothyl-induction model showed that administration of adrenocorticotropic hormone (ACTH) at time of seizure induction led to improved learning and memory in the animals despite no effect on seizure latency or duration. Administration of dexamethasone (Dex), a corticosteroid, did not have the same positive effect on learning and memory and has even been shown to exacerbate injury in a rat model of temporal lobe epilepsy. We hypothesized that ACTH exerted positive effects on cognitive outcomes through beneficial changes to gene expression and proposed that administration of ACTH at seizure induction would return gene-expression in the brain towards the normal pattern of expression in the Control animals whereas Dex would not. Twenty-six Sprague-Dawley rats were randomized into vehicle- Control, and ACTH-, Dex-, and vehicle- ELS. Rat pups were subjected to 60 flurothyl seizures from P5 to P14. After seizure induction, brains were removed and the hippocampus and PFC were dissected, RNA was extracted and sequenced, and differential expression analysis was performed using generalized estimating equations. Differential expression analysis showed that ACTH pushes gene expression in the brain back to a more normal state of expression through enrichment of pathways involved in supporting homeostatic balance and down-regulating pathways that might contribute to excitotoxic cell-damage post-ELS.

Modulating effects of FGF12 variants on NaV1.2 and NaV1.6 being associated with developmental and epileptic encephalopathy and Autism spectrum disorder: A case series

OBJECTIVE

Fibroblast Growth Factor 12 (FGF12) may represent an important modulator of neuronal network activity and has been associated with developmental and epileptic encephalopathy (DEE). We sought to identify the underlying pathomechanism of FGF12-related disorders.

METHODS

Patients with pathogenic variants in FGF12 were identified through published case reports, GeneMatcher and whole exome sequencing of own case collections. The functional consequences of two missense and two copy number variants (CNVs) were studied by co-expression of wildtype and mutant FGF12 in neuronal-like cells (ND7/23) with the sodium channels Na_V1.2 or Na_V1.6, including their beta-1 and beta-2 sodium channel subunits (SCN1B and SCN2B).

RESULTS

Four variants in FGF12 were identified for functional analysis: one novel FGF12 variant in a patient with autism spectrum disorder and three variants from previously published patients affected by DEE. We demonstrate the differential regulating effects of wildtype and mutant FGF12 on Na_V1.2 and Na_V1.6 channels. Here, FGF12 variants lead to a complex kinetic influence on Na_V1.2 and Na_V1.6, including loss- as well as gain-of function changes in fast and slow inactivation.

INTERPRETATION

We could demonstrate the detailed regulating effect of FGF12 on Na_V1.2 and Na_V1.6 and confirmed the complex effect of FGF12 on neuronal network activity. Our findings expand the phenotypic spectrum related to FGF12 variants and elucidate the underlying pathomechanism. Specific variants in FGF12-associated disorders may be amenable to precision treatment with sodium channel blockers.

FUNDING

DFG, BMBF, Hartwell Foundation, National Institute for Neurological Disorders and Stroke, IDDRC, ENGIN, NIH, ITMAT, ILAE, RES and GRIN.

Effective treatments for FGF12-related early-onset epileptic encephalopathies patients

BACKGROUND

FGF12 (FHF1) gene encodes voltage-gated sodium channel (Nav)-binding protein fibroblast growth factor homologous factor 1, which could cause seizures by regulating voltage dependence of Nav fast inactivation and neuron excitability. The most common pathogenic variant FGF12 c.341G > A related early-onset epileptic encephalopathies (EOEE) was characterized by intractable seizures and developmental disabilities.

RESULTS

Using whole exome sequencing, a de novo hotspot variant c.341G > A (NM_021032.4) of FGF12 was identified in three unrelated EOEE probands. All probands were seizure free after a combination treatment of valproic acid (VPA) and topiramate (TPM). The motor and cognitive skills in two probands were improved due to the early and effective treatment. In order to compare the effectiveness of different treatment strategies for the disease, a review of treatments for FGF12-related epilepsy was made.

CONCLUSION

We reported three FGF12 c.341G > A related EOEE patients responded well to a combination antiepileptic therapy of VPA and TPM. The current study is the first to describe the combination therapy of VPA and TPM in FGF12 c.341G > A related EOEE patients. This study may contribute to future medication consultation for intractable epilepsy with FGF12 hotspot variants.

Production of bioactive recombinant human fibroblast growth factor 12 using a new transient expression vector in E. coli and its neuroprotective effects

In recent years, an increasing number of studies have shown that fibroblast growth factor 12 (FGF12) plays important roles in regulating neural development and function. Importantly, changes of FGF12 expression are thought to be related to the pathophysiology of many neurological diseases. However, little research has been performed to explore the protective effect of FGF12 on nerve damage. This study aims to explore its neuroprotective effects using our recombinant humanized FGF12 (rhFGF12). The hFGF12 gene was cloned and ligated into an expression vector to construct a recombinant plasmid pET-3a-hFGF12. Single colonies were screened to obtain high expression engineering strains, and fermentation and purification protocols for rhFGF12 were designed and optimized. The biological activities and related mechanisms of rhFGF12 were investigated by MTT assay using NIH3T3 and PC12 cell lines. The in vitro neurotoxicity model of H₂O₂-induced oxidative injury in PC12 cells was established to explore the protective effects of rhFGF12. The results indicate that the beneficial effects of rhFGF12 were most likely achieved by promoting cell proliferation and reducing apoptosis. Moreover, a transgenic zebrafish (islet) with strong GFP fluorescence in the motor neurons of the hindbrain was used to establish a central injury model caused by mycophenolate mofetil (MMF). The results suggested that rhFGF12 could ameliorate central injury induced by MMF in zebrafish. In conclusion, we have established an efficient method to express and purify active rhFGF12 using an Escherichia coli expression system. Besides, rhFGF12 plays a protective effect of on nerve damage, and it provides a promising therapeutic approach for nerve injury. KEY POINTS: • Effective expression and purification of bioactive rhFGF12 protein in E. coli. • ERK/MAPK pathway is involved in rhFGF12-stimulated proliferation on PC12 cells. • The rhFGF12 has the neuroprotective effects by inhibiting apoptosis.

Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation

OBJECTIVE

Fibroblast growth factor homologous factors (FHFs) are brain and cardiac sodium channel-binding proteins that modulate channel density and inactivation gating. A recurrent de novo gain-of-function missense mutation in the FHF1(FGF12) gene (p.Arg52His) is associated with early infantile epileptic encephalopathy 47 (EIEE47; Online Mendelian Inheritance in Man database 617166). To determine whether the FHF1 missense mutation is sufficient to cause EIEE and to establish an animal model for EIEE47, we sought to engineer this mutation into mice.

METHODS

The Arg52His mutation was introduced into fertilized eggs by CRISPR (clustered regularly interspaced short palindromic repeats) editing to generate Fhf1^{R52H /F+} mice. Spontaneous epileptiform events in Fhf1^{R52H /+} mice were assessed by cortical electroencephalography (EEG) and video monitoring. Basal heart rhythm and seizure-induced arrhythmia were recorded by electrocardiography. Modulation of cardiac sodium channel inactivation by FHF1B_R52H protein was assayed by voltage-clamp recordings of FHF-deficient mouse cardiomyocytes infected with adenoviruses expressing wild-type FHF1B or FHF1B_R52H protein.

RESULTS

All Fhf1^{R52H /+} mice experienced seizure or seizurelike episodes with lethal ending between 12 and 26 days of age. EEG recordings in 19-20-day-old mice confirmed sudden unexpected death in epilepsy (SUDEP) as severe tonic seizures immediately preceding loss of brain activity and death. Within 2-53 s after lethal seizure onset, heart rate abruptly declined from 572 ± 16 bpm to 108 ± 15 bpm, suggesting a parasympathetic surge accompanying seizures that may have contributed to SUDEP. Although ectopic overexpression of FHF1B_R52H in cardiomyocytes induced a 15-mV depolarizing shift in voltage of steady-state sodium channel inactivation and slowed the rate of channel inactivation, heart rhythm was normal in Fhf1^{R52H /+} mice prior to seizure.

SIGNIFICANCE

The Fhf1 missense mutation p.Arg52His induces epileptic encephalopathy with full penetrance in mice. Both Fhf1 (p.Arg52His) and Scn8a (p.Asn1768Asp) missense mutations enhance sodium channel Na_v 1.6 currents and induce SUDEP with bradycardia in mice, suggesting an FHF1/Na_v 1.6 functional axis underlying altered brain sodium channel gating in epileptic encephalopathy.

Missense variants in the N-terminal domain of the A isoform of FHF2/FGF13 cause an X-linked developmental and epileptic encephalopathy

Fibroblast growth factor homologous factors (FHFs) are intracellular proteins which regulate voltage-gated sodium (Nav) channels in the brain and other tissues. FHF dysfunction has been linked to neurological disorders including epilepsy. Here, we describe two sibling pairs and three unrelated males who presented in infancy with intractable focal seizures and severe developmental delay. Whole-exome sequencing identified hemi- and heterozygous variants in the N-terminal domain of the A isoform of FHF2 (FHF2A). The X-linked FHF2 gene (also known as FGF13) has alternative first exons which produce multiple protein isoforms that differ in their N-terminal sequence. The variants were located at highly conserved residues in the FHF2A inactivation particle that competes with the intrinsic fast inactivation mechanism of Nav channels. Functional characterization of mutant FHF2A co-expressed with wild-type Nav1.6 (SCN8A) revealed that mutant FHF2A proteins lost the ability to induce rapid-onset, long-term blockade of the channel while retaining pro-excitatory properties. These gain-of-function effects are likely to increase neuronal excitability consistent with the epileptic potential of FHF2 variants. Our findings demonstrate that FHF2 variants are a cause of infantile-onset developmental and epileptic encephalopathy and underline the critical role of the FHF2A isoform in regulating Nav channel function.

Clinical Application of Whole Exome Sequencing to Identify Rare but Remediable Neurologic Disorders

Background: The aim of this study was to describe the application of whole exome sequencing (WES) in the accurate genetic diagnosis and personalized treatment of extremely rare neurogenetic disorders. Methods: From 2017 to 2019, children with neurodevelopmental symptoms were evaluated using WES in the pediatric neurology clinic and medical genetics center. The clinical presentation, laboratory findings including the genetic results from WES, and diagnosis-based treatment and outcomes of the four patients are discussed. Results: A total of 376 children with neurodevelopmental symptom were evaluated by WES, and four patients (1.1%) were diagnosed with treatable neurologic disorders. Patient 1 (Pt 1) showed global muscle hypotonia, dysmorphic facial features, and multiple anomalies beginning in the perinatal period. Pt 1 was diagnosed with congenital myasthenic syndrome 22 of PREPL deficiency. Pt 2 presented with hypotonia and developmental arrest and was diagnosed with autosomal recessive dopa-responsive dystonia due to TH deficiency. Pt 3, who suffered from intractable epilepsy and progressive cognitive decline, was diagnosed with epileptic encephalopathy 47 with a heterozygous FGF12 mutation. Pt 4 presented with motor delay and episodic ataxia and was diagnosed with episodic ataxia type II (heterozygous CACNA1A mutation). The patients’ major neurologic symptoms were remarkably relieved with pyridostigmine (Pt 1), levodopa (Pt 2), sodium channel blocker (Pt 3), and acetazolamide (Pt 4), and most patients regained developmental milestones in the follow-up period (0.4 to 3 years). Conclusions: The early application of WES helps in the identification of extremely rare genetic diseases, for which effective treatment modalities exist. Ultimately, WES resulted in optimal clinical outcomes of affected patients.

Predicting functional effects of missense variants in voltage-gated sodium and calcium channels

Malfunctions of voltage-gated sodium and calcium channels (encoded by SCNxA and CACNA1x family genes, respectively) have been associated with severe neurologic, psychiatric, cardiac, and other diseases. Altered channel activity is frequently grouped into gain or loss of ion channel function (GOF or LOF, respectively) that often corresponds not only to clinical disease manifestations but also to differences in drug response. Experimental studies of channel function are therefore important, but laborious and usually focus only on a few variants at a time. On the basis of known gene-disease mechanisms of 19 different diseases, we inferred LOF (n = 518) and GOF (n = 309) likely pathogenic variants from the disease phenotypes of variant carriers. By training a machine learning model on sequence- and structure-based features, we predicted LOF or GOF effects [area under the receiver operating characteristics curve (ROC) = 0.85] of likely pathogenic missense variants. Our LOF versus GOF prediction corresponded to molecular LOF versus GOF effects for 87 functionally tested variants in SCN1/2/8A and CACNA1I (ROC = 0.73) and was validated in exome-wide data from 21,703 cases and 128,957 controls. We showed respective regional clustering of inferred LOF and GOF nucleotide variants across the alignment of the entire gene family, suggesting shared pathomechanisms in the SCNxA/CACNA1x family genes.

Defining the phenotype of FHF1 developmental and epileptic encephalopathy

Fibroblast growth-factor homologous factor (FHF1) gene variants have recently been associated with developmental and epileptic encephalopathy (DEE). FHF1 encodes a cytosolic protein that modulates neuronal sodium channel gating. We aim to refine the electroclinical phenotypic spectrum of patients with pathogenic FHF1 variants. We retrospectively collected clinical, genetic, neurophysiologic, and neuroimaging data of 17 patients with FHF1-DEE. Sixteen patients had recurrent heterozygous FHF1 missense variants: 14 had the recurrent p.Arg114His variant and two had a novel likely pathogenic variant p.Gly112Ser. The p.Arg114His variant is associated with an earlier onset and more severe phenotype. One patient carried a chromosomal microduplication involving FHF1. Twelve patients carried a de novo variant, five (29.5%) inherited from parents with gonadic or somatic mosaicism. Seizure onset was between 1 day and 41 months; in 76.5% it was within 30 days. Tonic seizures were the most frequent seizure type. Twelve patients (70.6%) had drug-resistant epilepsy, 14 (82.3%) intellectual disability, and 11 (64.7%) behavioral disturbances. Brain magnetic resonance imaging (MRI) showed mild cerebral and/or cerebellar atrophy in nine patients (52.9%). Overall, our findings expand and refine the clinical, EEG, and imaging phenotype of patients with FHF1-DEE, which is characterized by early onset epilepsy with tonic seizures, associated with moderate to severe ID and psychiatric features.

Analysis of lncRNAs Expression Profiles in Hair Follicle of Hu Sheep Lambskin

Lambskin of the Hu sheep exhibits high economic value due to its water-wave pattern. Wool curvature is the key factor of the pattern types and quality of lambskin, and it is formed by the interaction between dermal papilla cells and hair matrix cells in the hair follicle, which is regulated by various genes and signaling pathways. Herein, three full-sibling pairs of two-day-old healthy lambs (n = 6) were divided into a straight wool group (ST) and small waves group (SM) with three repetitions. RNA-seq was applied to determine the expression profile of mRNAs and lncRNAs in Hu sheep hair follicles. 25 differentially expressed mRNAs and 75 differentially expressed lncRNAs were found between SM and ST. FGF12, ATP1B4, and TCONS_00279168 were probably associated with hair follicle development. Then, Gene Ontology (GO) and KEGG enrichment analysis were implemented for the functional annotation of target genes of differentially expressed lncRNAs. The results showed that many genes, such as FGF12 and ATP1B4, were found enriched in PI3K-Akt signaling, MAPK signaling, and Ras signaling pathway associated with hair follicle growth and development. In addition, the interaction network of differentially expressed lncRNAs and mRNAs showed that a total of 6 differentially expressed lncRNAs were associated with 12 differentially expressed mRNAs, which may be as candidate mRNAs and lncRNAs. TCONS_00279168 may target ATP1B4 and FGF12 to regulate MAPK, PI3K-Akt, Ras signaling pathways involved in the sheep hair follicle development process. These results will provide the basis for exploring hair follicle development.

Epilepsy phenotype in individuals with chromosomal duplication encompassing FGF12

Intragenic mutations in FGF12 are associated with intractable seizures, developmental regression, intellectual disability, ataxia, hypotonia, and feeding difficulties. FGF12 duplications are rarely reported, but it was suggested that those might have a similar gain-of-function effect and lead to a more or less comparable phenotype. A favorable response to the sodium blocker phenytoin was reported in several cases, both in patients with an intragenic mutation and in patients with a duplication of FGF12. We report three individuals from two families with FGF12 duplications. The duplications are flanked and probably mediated by two long interspersed nuclear elements (LINEs). The duplication cases show phenotypic overlap with the cases with intragenic mutations. Though the onset of epilepsy might be later, after the onset of seizures both groups show developmental stagnation and regression in several cases. This illustrates and further confirms that chromosomal FGF12 duplications and intragenic gain-of-function mutations yield overlapping phenotypes.

The expanding spectrum of movement disorders in genetic epilepsies

An ever-increasing number of neurogenetic conditions presenting with both epilepsy and atypical movements are now recognized. These disorders within the 'genetic epilepsy-dyskinesia' spectrum are clinically and genetically heterogeneous. Increased clinical awareness is therefore necessary for a rational diagnostic approach. Furthermore, careful interpretation of genetic results is key to establishing the correct diagnosis and initiating disease-specific management strategies in a timely fashion. In this review we describe the spectrum of movement disorders associated with genetically determined epilepsies. We also propose diagnostic strategies and putative pathogenic mechanisms causing these complex syndromes associated with both seizures and atypical motor control. WHAT THIS PAPER ADDS: Implicated genes encode proteins with very diverse functions. Pathophysiological mechanisms by which epilepsy and movement disorder phenotypes manifest are often not clear. Early diagnosis of treatable disorders is essential and next generation sequencing may be required.

Entire FGF12 duplication by complex chromosomal rearrangements associated with West syndrome

Complex rearrangements of chromosomes 3 and 9 were found in a patient presenting with severe epilepsy, developmental delay, dysmorphic facial features, and skeletal abnormalities. Molecular cytogenetic analysis revealed 46,XX.ish der(9)(3qter→3q28::9p21.1→9p22.3::9p22.3→9qter)(RP11-368G14+,RP11-299O8-,RP11-905L2++,RP11-775E6++). Her dysmorphic features are consistent with 3q29 microduplication syndrome and inv dup del(9p). Trio-based WES of the patient revealed no pathogenic single nucleotide variants causing epilepsy, but confirmed a 3q28q29 duplication involving FGF12, which encodes fibroblast growth factor 12. FGF12 positively regulates the activity of voltage-gated sodium channels. Recently, only one recurrent gain-of-function variant [NM_021032.4:c.341G>A:p.(Arg114His)] in FGF12 was found in a total of 10 patients with severe early-onset epilepsy. We propose that the patient's entire FGF12 duplication may be analogous to the gain-of-function variant in FGF12 in the epileptic phenotype of this patient.

The Epilepsy Genetics Initiative: Systematic reanalysis of diagnostic exomes increases yield

OBJECTIVE

The Epilepsy Genetics Initiative (EGI) was formed in 2014 to create a centrally managed database of clinically generated exome sequence data. EGI performs systematic research-based reanalysis to identify new molecular diagnoses that were not possible at the time of initial sequencing and to aid in novel gene discovery. Herein we report on the efficacy of this approach 3 years after inception.

METHODS

One hundred sixty-six individuals with epilepsy who underwent diagnostic whole exome sequencing (WES) were enrolled, including 139 who had not received a genetic diagnosis. Sequence data were transferred to the EGI and periodically reevaluated on a research basis.

RESULTS

Eight new diagnoses were made as a result of updated annotations or the discovery of novel epilepsy genes after the initial diagnostic analysis was performed. In five additional cases, we provided new evidence to support or contradict the likelihood of variant pathogenicity reported by the laboratory. One novel epilepsy gene was discovered through dual interrogation of research and clinically generated WES.

SIGNIFICANCE

EGI's diagnosis rate of 5.8% represents a considerable increase in diagnostic yield and demonstrates the value of periodic reinterrogation of whole exome data. The initiative's contributions to gene discovery underscore the importance of data sharing and the value of collaborative enterprises.

Allosteric regulators selectively prevent Ca2+-feedback of CaV and NaV channels

Calmodulin (CaM) serves as a pervasive regulatory subunit of Ca_V1, Ca_V2, and Na_V1 channels, exploiting a functionally conserved carboxy-tail element to afford dynamic Ca²⁺-feedback of cellular excitability in neurons and cardiomyocytes. Yet this modularity counters functional adaptability, as global changes in ambient CaM indiscriminately alter its targets. Here, we demonstrate that two structurally unrelated proteins, SH3 and cysteine-rich domain (stac) and fibroblast growth factor homologous factors (fhf) selectively diminish Ca²⁺/CaM-regulation of Ca_V1 and Na_V1 families, respectively. The two proteins operate on allosteric sites within upstream portions of respective channel carboxy-tails, distinct from the CaM-binding interface. Generalizing this mechanism, insertion of a short RxxK binding motif into Ca_V1.3 carboxy-tail confers synthetic switching of CaM regulation by Mona SH3 domain. Overall, our findings identify a general class of auxiliary proteins that modify Ca²⁺/CaM signaling to individual targets allowing spatial and temporal orchestration of feedback, and outline strategies for engineering Ca²⁺/CaM signaling to individual targets.

Two Japanese cases of epileptic encephalopathy associated with an FGF12 mutation

A heterozygous mutation in the fibroblast growth factor 12 (FGF12) gene, which elevates the voltage dependence of neuronal sodium channel fast inactivation, was recently identified in some patients with epileptic encephalopathy. Here we report 1 Japanese patient diagnosed with early infantile epileptic encephalopathy (EIEE) and another diagnosed with epilepsy of infancy with migrating focal seizures (EIMFS). These 2 patients had an identical heterozygous missense mutation [c.341G>A:p.(Arg114His)] in FGF12 , which was identified with whole-exome sequencing. This mutation is identical to previously reported mutations in cases with early onset epileptic encephalopathy. One of our cases exhibited EIMFS, and this case responded to phenytoin and high-dose phenobarbital (PB). FGF12-related epileptic encephalopathy may exhibit diverse phenotypes and may respond to sodium channel blockers or high-dose PB.

Genetics update: Monogenetics, polygene disorders and the quest for modifying genes

The genetic channelopathies are a broad collection of diseases. Many ion channel genes demonstrate wide phenotypic pleiotropy, but nonetheless concerted efforts have been made to characterise genotype-phenotype relationships. In this review we give an overview of the factors that influence genotype-phenotype relationships across this group of diseases as a whole, using specific individual channelopathies as examples. We suggest reasons for the limitations observed in these relationships. We discuss the role of ion channel variation in polygenic disease and highlight research that has contributed to unravelling the complex aetiological nature of these conditions. We focus specifically on the quest for modifying genes in inherited channelopathies, using the voltage-gated sodium channels as an example. Epilepsy related to genetic channelopathy is one area in which precision medicine is showing promise. We will discuss the successes and limitations of precision medicine in these conditions. This article is part of the Special Issue entitled 'Channelopathies.'

Heterogeneity of FHF1 related phenotype: Novel case with early onset severe attacks of apnea, partial mitochondrial respiratory chain complex II deficiency, neonatal onset seizures without neurodegeneration

INTRODUCTION/OBJECTIVES

We report the case of a child prospectively followed in our institution for a severe, neonatal onset epilepsy presenting with severe attacks of apnea that were not initially recognized as seizure since they were not associated with any abnormal movement and since interictal EEG was normal. Recording of attacks using prolonged video-EEG recording allowed to confirm the diagnosis of epileptic seizures.

RESULTS

Using whole exome sequencing we found a de novo heterozygous, missense mutation of FHF1 (p.Arg52His, NM_004113), a mutation that has been very recently described in 7 patients with an early onset epileptic encephalopathy. The initial workup showed a partial deficit of the complex II of the respiratory chain in muscle and liver. The prospective follow-up demonstrated that 2 drugs seemed to be more effective than the others: sodium blocker carbamazepine, and serotonin reuptake blocker fluoxetine. GABAergic drugs seemed to be ineffective. No drug aggravated the epilepsy.

DISCUSSION

This case report contributes to the description of an emerging phenotype for this condition.

WITHDRAWN: Genetics update: Monogenetics, polygene disorders and the quest for modifying genes

The Publisher regrets that this article is an accidental duplication of an article that has already been published, https://doi.org/10.1016/j.neuropharm.2017.10.013. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Post-translational dysfunctions in channelopathies of the nervous system

Channelopathies comprise various diseases caused by defects of ion channels. Modifications of their biophysical properties are common and have been widely studied. However, ion channels are heterogeneous multi-molecular complexes that are extensively modulated and undergo a maturation process comprising numerous steps of structural modifications and intracellular trafficking. Perturbations of these processes can give rise to aberrant channels that cause pathologies. Here we review channelopathies of the nervous system associated with dysfunctions at the post-translational level (folding, trafficking, degradation, subcellular localization, interactions with associated proteins and structural post-translational modifications). We briefly outline the physiology of ion channels' maturation and discuss examples of defective mechanisms, focusing in particular on voltage-gated sodium channels, which are implicated in numerous neurological disorders. We also shortly introduce possible strategies to develop therapeutic approaches that target these processes. This article is part of the Special Issue entitled 'Channelopathies.'

De novo FGF12 mutation in 2 patients with neonatal-onset epilepsy

Objective:

We describe 2 additional patients with early-onset epilepsy with a de novo FGF12 mutation.

Methods:

Whole-exome sequencing was performed in 2 unrelated patients with early-onset epilepsy and their unaffected parents. Genetic variants were assessed by comparative trio analysis. Clinical evolution, EEG, and neuroimaging are described. The phenotype and response to treatment was reviewed and compared to affected siblings in the original report.

Results:

We identified the same FGF12 de novo mutation reported previously (c.G155A, p.R52H) in 2 additional patients with early-onset epilepsy. Similar to the original brothers described, both presented with tonic seizures in the first month of life. In the first patient, seizures responded to sodium channel blockers and her development was normal at 11 months. Patient 2 is a 15-year-old girl with treatment-resistant focal epilepsy, moderate intellectual disability, and autism. Carbamazepine (sodium channel blocker) was tried later in her course but not continued due to an allergic reaction.

Conclusions:

The identification of a recurrent de novo mutation in 2 additional unrelated probands with early-onset epilepsy supports the role of FGF12 p.R52H in disease pathogenesis. Affected carriers presented with similar early clinical phenotypes; however, this report expands the phenotype associated with this mutation which contrasts with the progressive course and early mortality of the siblings in the original report.