Two Japanese cases of epileptic encephalopathy associated with an FGF12 mutation

Phenotyping of FGF12AV52H mutation in mouse implies a complex FGF12 network

Pathogenic missense mutation of the FGF12 gene is responsible for a variable disease phenotypic spectrum. Disease-specific therapies require precise dissection of the relationship between different mutations and phenotypes. The lack of a proper animal model hinders the investigation of related diseases, such as early-onset epileptic encephalopathy. Here, an FGF12AV52H mouse model was generated using CRISPR/Cas9 technology, which altered the A isoform without affecting the B isoform. The FGF12AV52H mice exhibited seizure susceptibility, while no spontaneous seizures were observed. The increased excitability in dorsal hippocampal CA3 neurons was confirmed by patch-clamp recordings. Furthermore, immunostaining showed that the balance of excitatory/inhibitory neurons in the hippocampus of the FGF12AV52H mice was perturbed. The increases in inhibitory SOM+ neurons and excitatory CaMKII+ neurons were heterogeneous. Moreover, the locomotion, anxiety levels, risk assessment behavior, social behavior, and cognition of the FGF12AV52H mice were investigated by elevated plus maze, open field, three-chamber sociability, and novel object tests, respectively. Cognition deficit, impaired risk assessment, and social behavior with normal social indexes were observed, implying complex consequences of V52H FGF12A in mice. Together, these data suggest that the function of FGF12A in neurons can be immediate or long-term and involves modulation of ion channels and the differentiation and maturation of neurons. The FGF12AV52H mouse model increases the understanding of the function of FGF12A, and it is of great importance for revealing the complex network of the FGF12 gene in physiological and pathological processes.

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.

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.

Biallelic structural variations within FGF12 detected by long-read sequencing in epilepsy

We discovered biallelic intragenic structural variations (SVs) in FGF12 by applying long-read whole genome sequencing to an exome-negative patient with developmental and epileptic encephalopathy (DEE). We also found another DEE patient carrying a biallelic (homozygous) single-nucleotide variant (SNV) in FGF12 that was detected by exome sequencing. FGF12 heterozygous recurrent missense variants with gain-of-function or heterozygous entire duplication of FGF12 are known causes of epilepsy, but biallelic SNVs/SVs have never been described. FGF12 encodes intracellular proteins interacting with the C-terminal domain of the alpha subunit of voltage-gated sodium channels 1.2, 1.5, and 1.6, promoting excitability by delaying fast inactivation of the channels. To validate the molecular pathomechanisms of these biallelic FGF12 SVs/SNV, highly sensitive gene expression analyses using lymphoblastoid cells from the patient with biallelic SVs, structural considerations, and Drosophila in vivo functional analysis of the SNV were performed, confirming loss-of-function. Our study highlights the importance of small SVs in Mendelian disorders, which may be overlooked by exome sequencing but can be detected efficiently by long-read whole genome sequencing, providing new insights into the pathomechanisms of human diseases.

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.

Predicting signaling pathways regulating demyelination in a rat model of lithium-pilocarpine-induced acute epilepsy: A proteomics study

Demyelination is observed in animal models of intractable epilepsy (IE). Epileptogenesis damages the myelin sheath and dysregulates oligodendrocyte precursor cell (OPC) development. However, the molecular pathways regulating demyelination in epilepsy are unclear. Here, we predicted the molecular mechanisms regulating demyelination in a rat model of lithium-pilocarpine hydrochloride-induced epilepsy. We identified DGKA/Mboat2/Inpp5j and NOS/Keratin 28 as the main target molecules that regulate demyelination via glycerolipid and glycerophospholipid metabolism, phosphatidylinositol signaling, and estrogen signaling in demyelinated forebrain slice cultures (FSCs). In seizure-like FCSs, the actin cytoskeleton was regulated by Cnp and MBP via Pak4/Tmsb4x (also known as Tβ4) and Kif5c/Kntc1. Tβ4 possibly prevented OPC differentiation and maturation and inhibited MBP phosphorylation via the p38MAPK/ERK1/JNK1 pathway. The MAPK signaling pathway was more likely activated in seizure-like FCSs than in demyelinated FCSs. pMBP expression was decreased in the hippocampus of lithium-pilocarpine hydrochloride-induced acute epilepsy rats. The expression of remyelination-related factors was suppressed in the hippocampus and corpus callosum in lithium-pilocarpine hydrochloride-induced epilepsy rats. These findings suggest that the actin cytoskeleton, Tβ4, and MAPK signaling pathways regulate the decrease in pMBP in the hippocampus in a rat model of epilepsy. Our results indicate that regulating the actin cytoskeleton, Tβ4, and MAPK signaling pathways may facilitate the prevention of demyelination in IE.

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.

New avenues in molecular genetics for the diagnosis and application of therapeutics to the epilepsies

Genetic epidemiology studies have shown that most epilepsies involve some genetic cause. In addition, twin studies have helped strengthen the hypothesis that in most patients with epilepsy, a complex inheritance is involved. More recently, with the development of high-density single-nucleotide polymorphism (SNP) microarrays and next-generation sequencing (NGS) technologies, the discovery of genes related to the epilepsies has accelerated tremendously. Especially, the use of whole exome sequencing (WES) has had a considerable impact on the identification of rare genetic variants with large effect sizes, including inherited or de novo mutations in severe forms of childhood epilepsies. The identification of pathogenic variants in patients with these childhood epilepsies provides many benefits for patients and families, such as the confirmation of the genetic nature of the diseases. This process will allow for better genetic counseling, more accurate therapy decisions, and a significant positive emotional impact. However, to study the genetic component of the more common forms of epilepsy, the use of high-density SNP arrays in genome-wide association studies (GWAS) seems to be the strategy of choice. As such, researchers can identify loci containing genetic variants associated with the common forms of epilepsy. The knowledge generated over the past two decades about the effects of the mutations that cause the monogenic epilepsy is tremendous; however, the scientific community is just starting to apply this information in order to generate better target treatments.

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.

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.

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.

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.