Epilepsy phenotype in individuals with chromosomal duplication encompassing FGF12

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 copy number variant associated with epileptic encephalopathy

FGF12 related epilepsy presents with variable phenotypes. We report another patient with a duplication involving the FGF12 gene who presented similar to other published cases having normal early development and responded to phenytoin.

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.

The FGF/FGFR system in the microglial neuroinflammation with Borrelia burgdorferi: likely intersectionality with other neurological conditions

BACKGROUND

Lyme neuroborreliosis, caused by the bacterium Borrelia burgdorferi affects both the central and peripheral nervous systems (CNS, PNS). The CNS manifestations, especially at later stages, can mimic/cause many other neurological conditions including psychiatric disorders, dementia, and others, with a likely neuroinflammatory basis. The pathogenic mechanisms associated with Lyme neuroborreliosis, however, are not fully understood.

METHODS

In this study, using cultures of primary rhesus microglia, we explored the roles of several fibroblast growth factor receptors (FGFRs) and fibroblast growth factors (FGFs) in neuroinflammation associated with live B. burgdorferi exposure. FGFR specific siRNA and inhibitors, custom antibody arrays, ELISAs, immunofluorescence and microscopy were used to comprehensively analyze the roles of these molecules in microglial neuroinflammation due to B. burgdorferi.

RESULTS

FGFR1-3 expressions were upregulated in microglia in response to B. burgdorferi. Inhibition of FGFR 1, 2 and 3 signaling using siRNA and three different inhibitors showed that FGFR signaling is proinflammatory in response to the Lyme disease bacterium. FGFR1 activation also contributed to non-viable B. burgdorferi mediated neuroinflammation. Analysis of the B. burgdorferi conditioned microglial medium by a custom antibody array showed that several FGFs are induced by the live bacterium including FGF6, FGF10 and FGF12, which in turn induce IL-6 and/or CXCL8, indicating a proinflammatory nature. To our knowledge, this is also the first-ever described role for FGF6 and FGF12 in CNS neuroinflammation. FGF23 upregulation, in addition, was observed in response to the Lyme disease bacterium. B. burgdorferi exposure also downregulated many FGFs including FGF 5, 7, 9, 11, 13, 16, 20 and 21. Some of the upregulated FGFs have been implicated in major depressive disorder (MDD) or dementia development, while the downregulated ones have been demonstrated to have protective roles in epilepsy, Parkinson's disease, Alzheimer's disease, spinal cord injury, blood-brain barrier stability, and others.

CONCLUSIONS

In this study we show that FGFRs and FGFs are novel inducers of inflammatory mediators in Lyme neuroborreliosis. It is likely that an unresolved, long-term (neuro)-Lyme infection can contribute to the development of other neurologic conditions in susceptible individuals either by augmenting pathogenic FGFs or by suppressing ameliorative FGFs or both.

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.

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.