FOXG1 syndrome: genotype-phenotype association in 83 patients with FOXG1 variants

The patient-specific mouse model with Foxg1 frameshift mutation provides insights into the pathophysiology of FOXG1 syndrome

Single allelic mutations in the FOXG1 gene lead to FOXG1 syndrome (FS). To understand the pathophysiology of FS, which vary depending on FOXG1 mutation types, patient-specific animal models are critical. Here, we report a patient-specific Q84Pfs heterozygous (Q84Pfs-Het) mouse model, which recapitulates various FS phenotypes across cellular, brain structural, and behavioral levels. Q84Pfs-Het cortex shows dysregulations of genes controlling cell proliferation, neuronal projection and migration, synaptic assembly, and synaptic vesicle transport. The Q84Pfs allele produces the N-terminal fragment of FOXG1 (Q84Pfs protein) in Q84Pfs-Het mouse brains, which forms intracellular speckles, interacts with FOXG1 full-length protein, and triggers the sequestration of FOXG1 to distinct subcellular domains. Q84Pfs protein promotes the radial glial cell identity and suppresses neuronal migration in the cortex. Our study uncovers the role of the FOXG1 fragment from FS-causing FOXG1 variants and identifies the genes involved in FS-like cellular and behavioral phenotypes, providing insights into the pathophysiology of FS.

The patient-specific mouse model with Foxg1 frameshift mutation provides insights into the pathophysiology of FOXG1 syndrome

Single allelic mutations in the forebrain-specific transcription factor gene FOXG1 lead to FOXG1 syndrome (FS). To decipher the disease mechanisms of FS, which vary depending on FOXG1 mutation types, patient-specific animal models are critical. Here, we report the first patient-specific FS mouse model, Q84Pfs heterozygous (Q84Pfs-Het) mice, which emulates one of the most predominant FS variants. Remarkably, Q84Pfs-Het mice recapitulate various human FS phenotypes across cellular, brain structural, and behavioral levels, such as microcephaly, corpus callosum agenesis, movement disorders, repetitive behaviors, and anxiety. Q84Pfs-Het cortex showed dysregulations of genes controlling cell proliferation, neuronal projection and migration, synaptic assembly, and synaptic vesicle transport. Interestingly, the FS-causing Q84Pfs allele produced the N-terminal fragment of FOXG1, denoted as Q84Pfs protein, in Q84Pfs-Het mouse brains. Q84Pfs fragment forms intracellular speckles, interacts with FOXG1 full-length protein, and triggers the sequestration of FOXG1 to distinct subcellular domains. Q84Pfs protein also promotes the radial glial cell identity and suppresses neuronal migration in the cortex. Together, our study uncovered the role of the FOXG1 fragment derived from FS-causing FOXG1 variants and identified the genes involved in FS-like cellular and behavioral phenotypes, providing essential insights into the pathophysiology of FS.

PLP1-Targeting Antisense Oligonucleotides Improve FOXG1 Syndrome Mice

FOXG1 syndrome is a rare neurodevelopmental disorder of the telencephalon, for which there is no cure. Underlying heterozygous pathogenic variants in the Forkhead Box G1 (FOXG1) gene with resulting impaired or loss of FOXG1 function lead to severe neurological impairments. Here, we report a patient with a de novo pathogenic single nucleotide deletion c.946del (p.Leu316Cysfs*10) of the FOXG1 gene that causes a premature protein truncation. To study this variant in vivo, we generated and characterized Foxg1 c946del mice that recapitulate hallmarks of the human disorder. Accordingly, heterozygous Foxg1 c946del mice display neurological symptoms with aberrant neuronal networks and increased seizure susceptibility. Gene expression profiling identified increased oligodendrocyte- and myelination-related gene clusters. Specifically, we showed that expression of the c946del mutant and of other pathogenic FOXG1 variants correlated with overexpression of proteolipid protein 1 (Plp1), a gene linked to white matter disorders. Postnatal administration of Plp1-targeting antisense oligonucleotides (ASOs) in Foxg1 c946del mice improved neurological deficits. Our data suggest Plp1 as a new target for therapeutic strategies mitigating disease phenotypes in FOXG1 syndrome patients.

FOXG1 variants can be associated with milder phenotypes than congenital Rett syndrome with unassisted walking and language development

Since 2008, FOXG1 haploinsufficiency has been linked to a severe neurodevelopmental phenotype resembling Rett syndrome but with earlier onset. Most patients are unable to sit, walk, or speak. For years, FOXG1 sequencing was only prescribed in such severe cases, limiting insight into the full clinical spectrum associated with this gene. Next-generation sequencing (NGS) now enables unbiased diagnostics. Through the European Reference Network for Rare Malformation Syndromes, Intellectual and Other Neurodevelopmental Disorders, we gathered data from patients with heterozygous FOXG1 variants presenting a mild phenotype, defined as able to speak and walk independently. We also reviewed data from three previously reported patients meeting our criteria. We identified five new patients with pathogenic FOXG1 missense variants, primarily in the forkhead domain, showing varying nonspecific intellectual disability and developmental delay. These features are not typical of congenital Rett syndrome and were rarely associated with microcephaly and epilepsy. Our findings are consistent with a previous genotype-phenotype analysis by Mitter et al. suggesting the delineation of five different FOXG1 genotype groups. Milder phenotypes were associated with missense variants in the forkhead domain. This information may facilitate prognostic assessments in children carrying a FOXG1 variant and improve the interpretation of new variants identified with genomic sequencing.

Foxg1 regulates translation of neocortical neuronal genes, including the main NMDA receptor subunit gene, Grin1

BACKGROUND

Mainly known as a transcription factor patterning the rostral brain and governing its histogenesis, FOXG1 has been also detected outside the nucleus; however, biological meaning of that has been only partially clarified.

RESULTS

Prompted by FOXG1 expression in cytoplasm of pallial neurons, we investigated its implication in translational control. We documented the impact of FOXG1 on ribosomal recruitment of Grin1-mRNA, encoding for the main subunit of NMDA receptor. Next, we showed that FOXG1 increases GRIN1 protein level by enhancing the translation of its mRNA, while not increasing its stability. Molecular mechanisms underlying this activity included FOXG1 interaction with EIF4E and, possibly, Grin1-mRNA. Besides, we found that, within murine neocortical cultures, de novo synthesis of GRIN1 undergoes a prominent and reversible, homeostatic regulation and FOXG1 is instrumental to that. Finally, by integrated analysis of multiple omic data, we inferred that FOXG1 is implicated in translational control of hundreds of neuronal genes, modulating ribosome engagement and progression. In a few selected cases, we experimentally verified such inference.

CONCLUSIONS

These findings point to FOXG1 as a key effector, potentially crucial to multi-scale temporal tuning of neocortical pyramid activity, an issue with profound physiological and neuropathological implications.

Foxg1 Modulation of the Prkcd Gene in the Lateral Habenula Mediates Trigeminal Neuralgia-Associated Anxiety-Like Behaviors in Mice

Trigeminal Neuralgia (TN) is a debilitating disorder frequently accompanied by mood complications such as depression and anxiety. The current study sought to elucidate the molecular underpinnings that contribute to the pathogenesis of TN and its associated anxiety. Employing a partial transection of the infraorbital nerve (pT-ION) in a murine model, we successfully induced sustained primary and secondary orofacial allodynia alongside anxiety-like behavioral manifestations. Transcriptome-wide gene microarray analyses revealed a marked upregulation of Foxg1 subsequent to pT-ION. Targeted knockdown of Foxg1, achieved through bilateral microinjection of adeno-associated virus harboring Foxg1-specific shRNA into the lateral habenula (LHb), resulted in a significant attenuation of both orofacial pain and anxiety-like behaviors. Subsequent RNA sequencing implicated Prkcd as a downstream effector gene modulated by Foxg1. Pharmacological inhibition of protein kinase C delta, encoded by Prkcd, within the LHb markedly ameliorated pT-ION-induced symptomatology. The dual luciferase assay revealed that Foxg1 substantially enhances the transcriptional activity of the Prkcd gene. Collectively, these findings indicate that trigeminal nerve injury leads to Foxg1 upregulation in the LHb, which in turn elevates the expression of Prkcd, culminating in the manifestation of orofacial pain and anxiety-like behaviors. This work offers promising therapeutic targets and a conceptual framework for the clinical management of TN and its psychological comorbidities.

Early Developmental Origins of Cortical Disorders Modeled in Human Neural Stem Cells

The implications of the early phases of human telencephalic development, involving neural stem cells (NSCs), in the etiology of cortical disorders remain elusive. Here, we explored the expression dynamics of cortical and neuropsychiatric disorder-associated genes in datasets generated from human NSCs across telencephalic fate transitions in vitro and in vivo. We identified risk genes expressed in brain organizers and sequential gene regulatory networks across corticogenesis revealing disease-specific critical phases, when NSCs are more vulnerable to gene dysfunctions, and converging signaling across multiple diseases. Moreover, we simulated the impact of risk transcription factor (TF) depletions on different neural cell types spanning the developing human neocortex and observed a spatiotemporal-dependent effect for each perturbation. Finally, single-cell transcriptomics of newly generated autism-affected patient-derived NSCs in vitro revealed recurrent alterations of TFs orchestrating brain patterning and NSC lineage commitment. This work opens new perspectives to explore human brain dysfunctions at the early phases of development.

Menin Deficiency Induces Autism-Like Behaviors by Regulating Foxg1 Transcription and Participates in Foxg1-Related Encephalopathy

FOXG1 syndrome is a developmental encephalopathy caused by FOXG1 (Forkhead box G1) mutations, resulting in high phenotypic variability. However, the upstream transcriptional regulation of Foxg1 expression remains unclear. This report demonstrates that both deficiency and overexpression of Men1 (protein: menin, a pathogenic gene of MEN1 syndrome known as multiple endocrine neoplasia type 1) lead to autism-like behaviors, such as social defects, increased repetitive behaviors, and cognitive impairments. Multifaceted transcriptome analyses revealed that Foxg1 signaling is predominantly altered in Men1 deficiency mice, through its regulation of the Alpha Thalassemia/Mental Retardation Syndrome X-Linked (Atrx) factor. Atrx recruits menin to bind to the transcriptional start region of Foxg1 and mediates the regulation of Foxg1 expression by H3K4me3 (Trimethylation of histone H3 lysine 4) modification. The deficits observed in menin deficient mice are rescued by the over-expression of Foxg1, leading to normalized spine growth and restoration of hippocampal synaptic plasticity. These findings suggest that menin may have a putative role in the maintenance of Foxg1 expression, highlighting menin signaling as a potential therapeutic target for Foxg1-related encephalopathy.

Foxg1 bimodally tunes L1-mRNA and -DNA dynamics in the developing murine neocortex

Foxg1 masters telencephalic development via a pleiotropic control over its progression. Expressed within the central nervous system (CNS), L1 retrotransposons are implicated in progression of its histogenesis and tuning of its genomic plasticity. Foxg1 represses gene transcription, and L1 elements share putative Foxg1-binding motifs, suggesting the former might limit telencephalic expression (and activity) of the latter. We tested such a prediction, in vivo as well as in engineered primary neural cultures, using loss- and gain-of-function approaches. We found that Foxg1-dependent, transcriptional L1 repression specifically occurs in neopallial neuronogenic progenitors and post-mitotic neurons, where it is supported by specific changes in the L1 epigenetic landscape. Unexpectedly, we discovered that Foxg1 physically interacts with L1-mRNA and positively regulates neonatal neopallium L1-DNA content, antagonizing the retrotranscription-suppressing activity exerted by Mov10 and Ddx39a helicases. To the best of our knowledge, Foxg1 represents the first CNS patterning gene acting as a bimodal retrotransposon modulator, limiting transcription of L1 elements and promoting their amplification, within a specific domain of the developing mouse brain.

C-terminal truncations in IQSEC2: implications for synaptic localization, guanine nucleotide exchange factor activity, and neurological manifestations

IQSEC2 gene on chromosome Xq11.22 encodes a member of guanine nucleotide exchange factor (GEF) protein that is implicated in the activation of ADP-ribosylation factors (Arfs) at the postsynaptic density (PSD), and plays a crucial role in synaptic transmission and dendritic spine formation. Alterations in IQSEC2 have been linked to X-linked intellectual developmental disorders including epilepsy and behavioral abnormalities. Of interest, truncating variants at the C-terminus of IQSEC2 can cause severe phenotypes, akin to truncating variants located in other regions. Here, we present a 5-year-old boy with severe intellectual disability and progressive epilepsy. The individual carried a nonsense variant p.Q1227* in the last exon of the IQSEC2 gene that was supposed to escape nonsense-mediated mRNA decay, thereby leading to a translation of C-terminus truncated IQSEC2 protein with residual activity. The functional analyses showed that the GEF activity of IQSEC2 Q1227* was compromised, and that the IQSEC2 Q1227* lacked preferential synaptic localization due to the absence of functional domains for binding to scaffolding proteins in the PSD. The impaired GEF activity and disrupted synaptic localization of the mutant IQSEC2 protein could impact dendritic and spine development in neurons, potentially explaining the patient's severe neurological manifestations. Our findings indicate that C-terminal truncations in IQSEC2, previously not well-characterized, may have significant pathogenic implications.

The Heart of Rett Syndrome: A Quantitative Analysis of Cardiac Repolarization

Background

Rett syndrome (RTT) is a developmental encephalopathy disorder that is associated with a high incidence of sudden death presumably from cardiorespiratory etiologies. Electrocardiogram (ECG) abnormalities, such as prolonged heart-rate corrected QT (QTc) interval, are markers of cardiac repolarization and are associated with potentially lethal ventricular arrhythmias. This study investigates the cardiac repolarization characteristics of RTT patients, including QTc and T-wave morphology characteristics.

Methods

A retrospective quantitative analysis on 110 RTT patients and 124 age and sex-matched healthy controls was conducted.

Results

RTT patients had longer QTc, more abnormal T-wave morphology, and greater heterogeneity of cardiac repolarization parameters compared to controls. Even RTT patients without prolonged QTc had more abnormal ECG and T-wave characteristics than controls. Among RTT patients, MECP2 patients had prolonged QTc compared to CDKL5 and FOXG1 patients. A subset of five RTT patients who died had normal QTc, but more abnormal T-wave morphology than the remaining RTT patients.

Conclusions

Cardiac repolarization abnormalities are present in RTT patients, even without long QTc. T-wave morphology is related to RTT genotype and may be predictive of mortality. These findings could be used to help the management and monitoring of RTT patients.

Gastrointestinal Dysfunction in Genetically Defined Neurodevelopmental Disorders

Gastrointestinal symptoms are common in most forms of neurodevelopment disorders (NDDs) such as in autism spectrum disorders (ASD). The current patient-reported outcome measures with validated questionnaires used in the general population of children without NDDS cannot be used in the autistic individuals. We explore here the multifactorial pathophysiology of ASD and the role of genetics and the environment in this disease spectrum and focus instead on possible diagnostics that could provide future objective insight into the connection of the gut-brain-microbiome in this disease entity. We provide our own data from both humans and a zebrafish model of ASD called Phelan-McDermid Syndrome. We hope that this review highlights the gaps in our current knowledge on many of these profound NDDs and that it provides a future framework upon which clinicians and researchers can build and network with other interested multidisciplinary specialties.

Rett Syndrome: A Tale of Altered Genetics, Synaptic Plasticity, and Neurodevelopmental Dynamics

Rett syndrome (RTT) is a neurodevelopmental disorder that is a leading cause of severe cognitive and physical impairment. RTT typically occurs in females, although rare cases of males with the disease exist. Its genetic cause, symptoms, and clinical progression timeline have also become well-documented since its initial discovery. However, a relatively late diagnosis and lack of an available cure signify that our understanding of the disease is incomplete. Innovative research methods and tools are thereby helping to fill gaps in our knowledge of RTT. Specifically, mouse models of RTT, video analysis, and retrospective parental analysis are well-established tools that provide valuable insights into RTT. Moreover, current and anticipated treatment options are improving the quality of life of the RTT patient population. Collectively, these developments are creating optimistic future perspectives for RTT.

The patient-specific mouse model with Foxg1 frameshift mutation uncovers the pathophysiology of FOXG1 syndrome

Single allelic mutations in the gene encoding the forebrain-specific transcription factor FOXG1 lead to FOXG1 syndrome (FS). Patient-specific animal models are needed to understand the etiology of FS, as FS patients show a wide spectrum of symptoms correlated with location and mutation type in the FOXG1 gene. Here we report the first patient-specific FS mouse model, Q84Pfs heterozygous (Q84Pfs-Het) mice, mimicking one of the most predominant single nucleotide variants in FS. Intriguingly, we found that Q84Pfs-Het mice faithfully recapitulate human FS phenotypes at the cellular, brain structural, and behavioral levels. Importantly, Q84Pfs-Het mice exhibited myelination deficits like FS patients. Further, our transcriptome analysis of Q84Pfs-Het cortex revealed a new role for FOXG1 in synapse and oligodendrocyte development. The dysregulated genes in Q84Pfs-Het brains also predicted motor dysfunction and autism-like phenotypes. Correspondingly, Q84Pfs-Het mice showed movement deficits, repetitive behaviors, increased anxiety, and prolonged behavior arrest. Together, our study revealed the crucial postnatal role of FOXG1 in neuronal maturation and myelination and elucidated the essential pathophysiology mechanisms of FS.

The clinical and sleep manifestations in children with FOXG1 syndrome

FOXG1 syndrome is a rare neurodevelopmental disorder associated with severe cognitive dysfunction, autistic behavior, and early-onset hyperkinetic movement disorders. Patients have also been reported to experience sleep disturbances. However, these findings are mainly based on subjective caregivers' reports, and limited by small case numbers. Moreover, no studies using objective evaluation tools, such as actigraphy, have been reported. We analyzed the clinical and sleep manifestations of children with FOXG1 syndrome registered in the International FOXG1 Research Foundation registry database. A total of 258 individuals with FOXG1 syndrome were included in this research. 132 (51.16%) had sleep disturbances. The more impaired of language acquisitions (absence of speech, OR: 3.99, 95%CI = 1.69-9.42, p = 0.002), hyperkinetic movement disorders (OR: 2.64, 95%CI = 1.34-5.20 p = 0.005) and feeding difficulties (OR: 2.81, 95% CI = 1.52-5.19, p = 0.001) were significantly associated with an increase in odds of sleep disturbance after adjusting for age, sex, and antiepileptic drugs. We also performed sleep studies on six individuals with FOXG1 syndrome using The Children's Sleep Habits Questionnaire (CSHQ), the Sleep Disturbance Scale for Children (SDSC), and 7-day data from Actiwatch. The Pittsburgh Sleep Quality Index (PSQI) and 7-day data from Actiwatch were also used to evaluate the sleep condition of their parents. The CSHQ scores revealed bedtime resistance, sleep onset delay, sleep duration, sleep anxiety, night-waking, and parasomnia. Sleep-wake transition disorders and disorders of initiating and maintaining sleep were also suggested by the SDSC scores. The children's actigraphy revealed short sleep durations, impaired sleep efficiency, longer wake after sleep onset, and frequent night-waking. All caregivers reported significantly higher PSQI scores, mildly declined sleep efficiency, and shorter total sleep duration. Sleep disturbances, especially in initiating and maintaining sleep, are common in individuals with FOXG1 syndrome and their caregivers. Sleep disorders in patients with FOXG1 syndrome and their caregivers should be investigated.

Prenatal Neurological Diagnosis: Challenges in Neuroimaging, Prognostic Counseling, and Prediction of Neurodevelopmental Outcomes

Prenatal diagnosis of fetal brain abnormalities is rapidly evolving with the advancement of neuroimaging techniques, thus adding value to prognostic counseling and perinatal management. However, challenges and uncertainties persist in prenatal counseling due to limitations of prenatal imaging, continued development and maturation of the brain structure, and the heterogeneity and paucity of outcome studies. This topical review of fetal neurological consultations highlights prenatally diagnosed brain abnormalities that challenged prognostic counseling and perinatal management. Representative cases across multiple centers that highlighted diagnostic challenges were selected. Charts were reviewed for neuroimaging, genetic evaluation, prenatal prognostic discussion, postnatal imaging and testing, and infant outcome. We present case studies with prenatal and postnatal information discussing prenatal testing, fetal MRI interpretation, and complexities in the prognostic counseling process. Advocating for large-scale multicenter studies and a national collaborative fetal neurological registry to help guide the ever-expanding world of prenatal diagnostics and prognostic counseling is critical to this field. Study of large-scale outcomes data from such a registry can better guide fetal neurological consultations and facilitate comprehensive multidisciplinary planning and program development for educational curriculum for fetal-neonatal neurology.

Precision medicine for developmental and epileptic encephalopathies in Africa-strategies for a resource-limited setting

PURPOSE

Sub-Saharan Africa bears the highest burden of epilepsy worldwide. A presumed proportion is genetic, but this etiology is buried under the burden of infections and perinatal insults in a setting of limited awareness and few options for testing. Children with developmental and epileptic encephalopathies (DEEs) are most severely affected by this diagnostic gap in Africa, because the rate of actionable findings is highest in DEE-associated genes.

METHODS

We tested 234 genetically naive South African children diagnosed with/possible DEE using gene panels, exome sequencing, and chromosomal microarray. Statistical comparison of electroclinical features in children with and children without candidate variants was performed to identify characteristics most likely predictive of a positive genetic finding.

RESULTS

Of the 41 (of 234) children with likely/pathogenic variants, 26 had variants supporting precision therapy. Multivariate regression modeling highlighted neonatal or infantile-onset seizures and movement abnormalities as predictive of a positive genetic finding. We used this, coupled with an emphasis on precision medicine outcomes, to propose the pragmatic "Think-Genetics" strategy for early recognition of a possible genetic etiology.

CONCLUSION

Our findings emphasize the importance of an early genetic diagnosis in DEE. We designed the Think-Genetics strategy for early recognition, appropriate interim management, and genetic testing for DEE in resource-constrained settings.

Differential vulnerability of adult neurogenic niches to dosage of the neurodevelopmental-disorder linked gene Foxg1

The transcription factor FOXG1 serves pleiotropic functions in brain development ranging from the regulation of precursor proliferation to the control of cortical circuit formation. Loss-of-function mutations and duplications of FOXG1 are associated with neurodevelopmental disorders in humans illustrating the importance of FOXG1 dosage for brain development. Aberrant FOXG1 dosage has been found to disrupt the balanced activity of glutamatergic and GABAergic neurons, but the underlying mechanisms are not fully understood. We report that FOXG1 is expressed in the main adult neurogenic niches in mice, i.e. the hippocampal dentate gyrus and the subependymal zone/olfactory bulb system, where neurogenesis of glutamatergic and GABAergic neurons persists into adulthood. These niches displayed differential vulnerability to increased FOXG1 dosage: high FOXG1 levels severely compromised survival and glutamatergic dentate granule neuron fate acquisition in the hippocampal neurogenic niche, but left neurogenesis of GABAergic neurons in the subependymal zone/olfactory bulb system unaffected. Comparative transcriptomic analyses revealed a significantly higher expression of the apoptosis-linked nuclear receptor Nr4a1 in FOXG1-overexpressing hippocampal neural precursors. Strikingly, pharmacological interference with NR4A1 function rescued FOXG1-dependent death of hippocampal progenitors. Our results reveal differential vulnerability of neuronal subtypes to increased FOXG1 dosage and suggest that activity of a FOXG1/NR4A1 axis contributes to such subtype-specific response.

Identification of a de novo mutation of the FOXG1 gene and comprehensive analysis for molecular factors in Chinese FOXG1-related encephalopathies

Background

FOXG1-related encephalopathy, also known as FOXG1 syndrome or FOXG1-related disorder, affects most aspects of development and causes microcephaly and brain malformations. This syndrome was previously considered to be the congenital variant of Rett syndrome. The abnormal function or expression of FOXG1, caused by intragenic mutations, microdeletions or microduplications, was considered to be crucial pathological factor for this disorder. Currently, most of the FOXG1-related encephalopathies have been identified in Europeans and North Americans, and relatively few Chinese cases were reported.

Methods

Array-Comparative Genomic Hybridization (Array-CGH) and whole-exome sequencing (WES) were carried out for the proband and her parent to detect pathogenic variants.

Results

A de novo nonsense mutation (c.385G>T, p.Glu129Ter) of FOXG1 was identified in a female child in a cohort of 73 Chinese children with neurodevelopmental disorders/intellectual disorders (NDDs/IDs). In order to have a comprehensive view of FOXG1-related encephalopathy in China, relevant published reports were browsed and twelve cases with mutations in FOXG1 or copy number variants (CNVs) involving FOXG1 gene were involved in the analysis eventually. Feeding difficulties, seizures, delayed speech, corpus callosum hypoplasia and underdevelopment of frontal and temporal lobes occurred in almost all cases. Out of the 12 cases, eight patients (66.67%) had single-nucleotide mutations of FOXG1 gene and four patients (33.33%) had CNVs involving FOXG1 (3 microdeletions and 1 microduplication). The expression of FOXG1 could also be potentially disturbed by deletions of several brain-active regulatory elements located in intergenic FOXG1-PRKD1 region. Further analysis indicated that PRKD1 might be a cooperating factor to regulate the expression of FOXG1, MECP2 and CDKL5 to contribute the RTT/RTT-like disorders.

Discussion

This re-analysis would broaden the existed knowledge about the molecular etiology and be helpful for diagnosis, treatment, and gene therapy of FOXG1-related disorders in the future.

Behavioral and brain anatomical analysis of Foxg1 heterozygous mice

FOXG1 Syndrome (FS) is a devastating neurodevelopmental disorder that is caused by a heterozygous loss-of-function (LOF) mutation of the FOXG1 gene, which encodes a transcriptional regulator important for telencephalic brain development. People with FS have marked developmental delays, impaired ambulation, movement disorders, seizures, and behavior abnormalities including autistic features. Current therapeutic approaches are entirely symptomatic, however the ability to rescue phenotypes in mouse models of other genetic neurodevelopmental disorders such as Rett syndrome, Angelman syndrome, and Phelan-McDermid syndrome by postnatal expression of gene products has led to hope that similar approaches could help modify the disease course in other neurodevelopmental disorders such as FS. While FoxG1 protein function plays a critical role in embryonic brain development, the ongoing adult expression of FoxG1 and behavioral phenotypes that present when FoxG1 function is removed postnatally provides support for opportunity for improvement with postnatal treatment. Here we generated a new mouse allele of Foxg1 that disrupts protein expression and characterized the behavioral and structural brain phenotypes in heterozygous mutant animals. These mutant animals display changes in locomotor behavior, gait, anxiety, social interaction, aggression, and learning and memory compared to littermate controls. Additionally, they have structural brain abnormalities reminiscent of people with FS. This information provides a framework for future studies to evaluate the potential for post-natal expression of FoxG1 to modify the disease course in this severe neurodevelopmental disorder.

Genetic heterogeneity in corpus callosum agenesis

The corpus callosum is the largest white matter structure connecting the two cerebral hemispheres. Agenesis of the corpus callosum (ACC), complete or partial, is one of the most common cerebral malformations in humans with a reported incidence ranging between 1.8 per 10,000 livebirths to 230–600 per 10,000 in children and its presence is associated with neurodevelopmental disability. ACC may occur as an isolated anomaly or as a component of a complex disorder, caused by genetic changes, teratogenic exposures or vascular factors. Genetic causes are complex and include complete or partial chromosomal anomalies, autosomal dominant, autosomal recessive or X-linked monogenic disorders, which can be either de novo or inherited. The extreme genetic heterogeneity, illustrated by the large number of syndromes associated with ACC, highlight the underlying complexity of corpus callosum development. ACC is associated with a wide spectrum of clinical manifestations ranging from asymptomatic to neonatal death. The most common features are epilepsy, motor impairment and intellectual disability. The understanding of the genetic heterogeneity of ACC may be essential for the diagnosis, developing early intervention strategies, and informed family planning. This review summarizes our current understanding of the genetic heterogeneity in ACC and discusses latest discoveries.

Hypoventilation and sleep hypercapnia in a case of congenital variant-like Rett syndrome

BACKGROUND

Breathing disturbances are often a primary clinical concern especially during wakefulness of the classic form of Rett syndrome, but data for atypical forms are lacking.

CASE PRESENTATION

We report the case of a 20-month-old female affected by Rett syndrome with congenital variant-like onset, characterized by severe hypotonia and neurodevelopment impairment. She presented hypoventilation, persistent periodic breathing, and sustained desaturation during sleep, without obstructive or mixed events. Pulse oximetry and capnography during wakefulness were strictly normal. To the best of our knowledge, this is the first case of a patient affected by a congenital variant of Rett syndrome presenting sleep hypercapnia. Hypotonia may play a major role in the genesis of hypoventilation and hypoxemia in our patient. Non-invasive ventilation led to quality-of-life improvements.

CONCLUSIONS

Thus, we suggest screening patients with congenital-like Rett syndrome through transcutaneous bedtime carbon dioxide and oxygen monitoring. Moreover, assisted control mode was a breakthrough to achieve adequate ventilation in our case.

Recommendations by the ClinGen Rett/Angelman-like expert panel for gene-specific variant interpretation methods

The genes MECP2, CDKL5, FOXG1, UBE3A, SLC9A6, and TCF4 present unique challenges for current ACMG/AMP variant interpretation guidelines. To address those challenges, the Rett and Angelman-like Disorders Variant Curation Expert Panel (Rett/AS VCEP) drafted gene-specific modifications. A pilot study was conducted to test the clarity and accuracy of using the customized variant interpretation criteria. Multiple curators obtained the same interpretation for 78 out of the 87 variants (~90%), indicating appropriate usage of the modified guidelines the majority of times by all the curators. The classification of 13 variants changed using these criteria specifications compared to when the variants were originally curated and as present in ClinVar. Many of these changes were due to internal data shared from laboratory members however some changes were because of changes in strength of criteria. There were no two-step classification changes and only 1 clinically relevant change (Likely pathogenic to VUS). The Rett/AS VCEP hopes that these gene-specific variant curation rules and the assertions provided help clinicians, clinical laboratories, and others interpret variants in these genes but also other fully penetrant, early-onset genes associated with rare disorders.

Zika virus induces FOXG1 nuclear displacement and downregulation in human neural progenitors

Congenital alterations in the levels of the transcription factor Forkhead box g1 (FOXG1) coding gene trigger "FOXG1 syndrome," a spectrum that recapitulates birth defects found in the "congenital Zika syndrome," such as microcephaly and other neurodevelopmental conditions. Here, we report that Zika virus (ZIKV) infection alters FOXG1 nuclear localization and causes its downregulation, thus impairing expression of genes involved in cell replication and apoptosis in several cell models, including human neural progenitor cells. Growth factors, such as EGF and FGF2, and Thr271 residue located in FOXG1 AKT domain, take part in the nuclear displacement and apoptosis protection, respectively. Finally, by progressive deletion of FOXG1 sequence, we identify the C-terminus and the residues 428-481 as critical domains. Collectively, our data suggest a causal mechanism by which ZIKV affects FOXG1, its target genes, cell cycle progression, and survival of human neural progenitors, thus contributing to microcephaly.

Behavioral Phenotypes of Foxg1 Heterozygous Mice

FOXG1 syndrome (FS, aka a congenital variant of Rett syndrome) is a recently defined rare and devastating neurodevelopmental disorder characterized by various symptoms, including severe intellectual disability, autistic features, involuntary, and continuous jerky movements, feeding problems, sleep disturbances, seizures, irritability, and excessive crying. FS results from mutations in a single allele of the FOXG1 gene, leading to impaired FOXG1 function. Therefore, in establishing mouse models for FS, it is important to test if heterozygous (HET) mutation in the Foxg1 gene, mimicking genotypes of the human FS individuals, also manifests phenotypes similar to their symptoms. We analyzed HET mice with a null mutation allele in a single copy of Foxg1, and found that they show various phenotypes resembling the symptoms of the human FS individuals. These include increased anxiety in the open field as well as impairment in object recognition, motor coordination, and fear learning and contextual and cued fear memory. Our results suggest that Foxg1 HET mice recapitulate at least some symptoms of the human FS individuals.

Combined in Silico Prediction Methods, Molecular Dynamic Simulation, and Molecular Docking of FOXG1 Missense Mutations: Effect on FoxG1 Structure and Its Interactions with DNA and Bmi-1 Protein

FoxG1 encoded by FOXG1 gene is a transcriptional factor interacting with the DNA of targeted genes as well as with several proteins to regulate the forebrain development. Mutations in the FOXG1 gene have been shown to cause a wide spectrum of brain disorders, including the congenital variant of Rett syndrome. In this study, the direct sequencing of FOXG1 gene revealed a novel c.645C > A (F215L) variant in the patient P1 and a de novo known one c.755G > A (G252D) in the patient P2. To investigate the putative impact of FOXG1 missense variants, a computational pipeline by the application of in silico prediction methods, molecular dynamic simulation, and molecular docking approaches was used. Bioinformatics analysis and molecular dynamics simulation have demonstrated that F215L and G252D variants found in the DNA binding domain are highly deleterious mutations that may cause the protein structure destabilization. On the other hand, molecular docking revealed that F215L mutant is likely to have a great impact on destabilizing the protein structure and the disruption of the Bmi-1 binding site quite significantly. Regarding G252D mutation, it seems to abolish the ability of FoxG1 to bind DNA target, affecting the transcriptional regulation of targeted genes. Our study highlights the usefulness of combined computational approaches, molecular dynamic simulation, and molecular docking for a better understanding of the dysfunctional effects of FOXG1 missense mutations and their role in the etiopathogenesis as well as in the genotype-phenotype correlation.

Analysis of X-inactivation status in a Rett syndrome natural history study cohort

BACKGROUND

Rett syndrome (RTT) is a rare neurodevelopmental disorder associated with pathogenic MECP2 variants. Because the MECP2 gene is subject to X-chromosome inactivation (XCI), factors including MECP2 genotypic variation, tissue differences in XCI, and skewing of XCI all likely contribute to the clinical severity of individuals with RTT.

METHODS

We analyzed the XCI patterns from blood samples of 320 individuals and their mothers. It includes individuals with RTT (n = 287) and other syndromes sharing overlapping phenotypes with RTT (such as CDKL5 Deficiency Disorder [CDD, n = 16]). XCI status in each proband/mother duo and the parental origin of the preferentially inactivated X chromosome were analyzed.

RESULTS

The average XCI ratio in probands was slightly increased compared to their unaffected mothers (73% vs. 69%, p = .0006). Among the duos with informative XCI data, the majority of individuals with classic RTT had their paternal allele preferentially inactivated (n = 180/220, 82%). In sharp contrast, individuals with CDD had their maternal allele preferentially inactivated (n = 10/12, 83%). Our data indicate a weak positive correlation between XCI skewing ratio and clinical severity scale (CSS) scores in classic RTT patients with maternal allele preferentially inactivated XCI (r_s  = 0.35, n = 40), but not in those with paternal allele preferentially inactivated XCI (r_s  = -0.06, n = 180). The most frequent MECP2 pathogenic variants were enriched in individuals with highly/moderately skewed XCI patterns, suggesting an association with higher levels of XCI skewing.

CONCLUSION

These results extend our understanding of the pathogenesis of RTT and other syndromes with overlapping clinical features by providing insight into the both XCI and the preferential XCI of parental alleles.

Sleep Disorders in Rett Syndrome and Rett-Related Disorders: A Narrative Review

Rett Syndrome (RTT) is a rare and severe X-linked developmental brain disorder that occurs primarily in females, with a ratio of 1:10.000. De novo mutations in the Methyl-CpG Binding protein 2 (MECP2) gene on the long arm of X chromosome are responsible for more than 95% cases of classical Rett. In the remaining cases (atypical Rett), other genes are involved such as the cyclin-dependent kinase-like 5 (CDKL5) and the forkhead box G1 (FOXG1). Duplications of the MECP2 locus cause MECP2 duplication syndrome (MDS) which concerns about 1% of male patients with intellectual disability. Sleep disorders are common in individuals with intellectual disability, while the prevalence in children is between 16 and 42%. Over 80% of individuals affected by RTT show sleep problems, with a higher prevalence in the first 7 years of life and some degree of variability in correlation to age and genotype. Abnormalities in circadian rhythm and loss of glutamate homeostasis play a key role in the development of these disorders. Sleep disorders, epilepsy, gastrointestinal problems characterize CDKL5 Deficiency Disorder (CDD). Sleep impairment is an area of overlap between RTT and MECP2 duplication syndrome along with epilepsy, regression and others. Sleep dysfunction and epilepsy are deeply linked. Sleep deprivation could be an aggravating factor of epilepsy and anti-comitial therapy could interfere in sleep structure. Epilepsy prevalence in atypical Rett syndrome with severe clinical phenotype is higher than in classical Rett syndrome. However, RTT present a significant lifetime risk of epilepsy too. Sleep disturbances impact on child's development and patients' families and the evidence for its management is still limited. The aim of this review is to analyze pathophysiology, clinical features, the impact on other comorbidities and the management of sleep disorders in Rett syndrome and Rett-related syndrome.

Paving Therapeutic Avenues for FOXG1 Syndrome: Untangling Genotypes and Phenotypes from a Molecular Perspective

Development of the central nervous system (CNS) depends on accurate spatiotemporal control of signaling pathways and transcriptional programs. Forkhead Box G1 (FOXG1) is one of the master regulators that play fundamental roles in forebrain development; from the timing of neurogenesis, to the patterning of the cerebral cortex. Mutations in the FOXG1 gene cause a rare neurodevelopmental disorder called FOXG1 syndrome, also known as congenital form of Rett syndrome. Patients presenting with FOXG1 syndrome manifest a spectrum of phenotypes, ranging from severe cognitive dysfunction and microcephaly to social withdrawal and communication deficits, with varying severities. To develop and improve therapeutic interventions, there has been considerable progress towards unravelling the multi-faceted functions of FOXG1 in the neurodevelopment and pathogenesis of FOXG1 syndrome. Moreover, recent advances in genome editing and stem cell technologies, as well as the increased yield of information from high throughput omics, have opened promising and important new avenues in FOXG1 research. In this review, we provide a summary of the clinical features and emerging molecular mechanisms underlying FOXG1 syndrome, and explore disease-modelling approaches in animals and human-based systems, to highlight the prospects of research and possible clinical interventions.

Autism spectrum disorder and comorbid neurodevelopmental disorders (ASD-NDDs): Clinical and genetic profile of a pediatric cohort

BACKGROUND

Autism spectrum disorder (ASD), a neurodevelopmental disorder, is featured by impaired social communication and restricted and repetitive behaviors and interests. ASD and comorbid neurodevelopmental disorders (ASD-NDDs), especially epilepsy and intellectual disability (ID)/global developmental delay (GDD) are frequently presented in genetic disorders. The aim of this study was to explore the clinical and genetic profile of ASD in combination with epilepsy or ID/GDD.

METHODS

We retrospectively analyzed the clinical characteristics, and genetic spectrum of pediatric patients presenting ASD-NDDs with proven genetic etiology. The pathogenicity of variants was conducted by molecular geneticists and clinicians complied with the guidelines of the American College of Medical Genetics and Genomics (ACMG).

RESULTS

Among 154 patients with ASD-NDDs, 79 (51.3%) patients gained a genetic diagnosis. Most patients (78/79, 98.7%) had comorbid ID or GDD, and 49 (49/79, 62.0%) had comorbid epilepsy. The clinical characteristics of those 79 patients were varied. 87 genetic variants were found among the 79 pedigrees. Most of the involved genes have roles in gene expression regulation (GER) and neuronal communication (NC). Most genes have been proven to be ASD-related genes, and some of them were not reported to contribute to ASD previously.

CONCLUSION

We summarized the genetic and clinical profile of 79 ASD-NDDs patients with proven genetic etiology. The genetic spectrum of ASD was expanded, and we highlighted a novel possible ASD candidate gene PRTG.

Exome Sequencing Reveals Novel Variants and Expands the Genetic Landscape for Congenital Microcephaly

Congenital microcephaly causes smaller than average head circumference relative to age, sex and ethnicity and is most usually associated with a variety of neurodevelopmental disorders. The underlying etiology is highly heterogeneous and can be either environmental or genetic. Disruption of any one of multiple biological processes, such as those underlying neurogenesis, cell cycle and division, DNA repair or transcription regulation, can result in microcephaly. This etiological heterogeneity manifests in a clinical variability and presents a major diagnostic and therapeutic challenge, leaving an unacceptably large proportion of over half of microcephaly patients without molecular diagnosis. To elucidate the clinical and genetic landscapes of congenital microcephaly, we sequenced the exomes of 191 clinically diagnosed patients with microcephaly as one of the features. We established a molecular basis for microcephaly in 71 patients (37%), and detected novel variants in five high confidence candidate genes previously unassociated with this condition. We report a large number of patients with mutations in tubulin-related genes in our cohort as well as higher incidence of pathogenic mutations in MCPH genes. Our study expands the phenotypic and genetic landscape of microcephaly, facilitating differential clinical diagnoses for disorders associated with most commonly disrupted genes in our cohort.

Identification of FOXG1 mutations in infantile hypotonia and postnatal microcephaly

ABSTRACT

FOXG1, located at chromosome 14q12, is critical for brain development, and patients with FOXG1 mutation exhibit developmental encephalopathy with high phenotypic variability, known as FOXG1 syndrome. Here, we report 3 cases of FOXG1 syndrome that presented with infantile hypotonia and microcephaly.A total of 145 children with developmental delay and/or hypotonia were evaluated by whole-exome sequencing (WES) in the pediatric neurology clinic and medical genetics center at Asan Medical Center Children's Hospital, from 2017 to 2019. Each FOXG1 mutation was confirmed by Sanger sequencing. The clinical findings of each patient with FOXG1 mutation were reviewed.WES identified de-novo, pathogenic, and heterozygous FOXG1 mutations in 3 of 145 patients in our patient cohort with developmental delay and/or hypotonia. The characteristics of brain magnetic resonance imaging (MRI) were reported as callosal anomaly, decrease in frontal volume, fornix thickening, and hypoplastic olfactory bulbs. A phenotype-genotype correlation was demonstrated as a patient with a novel missense mutation, c.761A > C (p.Tyr254Ser), in the forkhead domain had better outcome and milder brain abnormalities than the other 2 patients with truncating mutation in the Groucho binding domain site, c.958delC (p.Arg320Alafs), or N-terminal domain, c.506dup (p.Lys170GlnfsThe). Importantly, all 3 patients had hypoplastic olfactory bulbs on their brain MRI, which is a distinct and previously unrecognized feature of FOXG1 syndrome.This is the first report of FOXG1 syndrome in a Korean population; this condition accounts for 2% (3 of 145 patients) of our patient cohort with developmental delays and/or hypotonia. Our report contributes to understanding this extremely rare genetic condition in the clinical and genetic perspectives.

Programmed Cell Death Not as Sledgehammer but as Chisel: Apoptosis in Normal and Abnormal Craniofacial Patterning and Development

Coordination of craniofacial development involves an complex, intricate, genetically controlled and tightly regulated spatiotemporal series of reciprocal inductive and responsive interactions among the embryonic cephalic epithelia (both endodermal and ectodermal) and the cephalic mesenchyme — particularly the cranial neural crest (CNC). The coordinated regulation of these interactions is critical both ontogenetically and evolutionarily, and the clinical importance and mechanistic sensitivity to perturbation of this developmental system is reflected by the fact that one-third of all human congenital malformations affect the head and face. Here, we focus on one element of this elaborate process, apoptotic cell death, and its role in normal and abnormal craniofacial development. We highlight four themes in the temporospatial elaboration of craniofacial apoptosis during development, namely its occurrence at (1) positions of epithelial-epithelial apposition, (2) within intra-epithelial morphogenesis, (3) during epithelial compartmentalization, and (4) with CNC metameric organization. Using the genetic perturbation of Satb2, Pbx1/2, Fgf8, and Foxg1 as exemplars, we examine the role of apoptosis in the elaboration of jaw modules, the evolution and elaboration of the lambdoidal junction, the developmental integration at the mandibular arch hinge, and the control of upper jaw identity, patterning and development. Lastly, we posit that apoptosis uniquely acts during craniofacial development to control patterning cues emanating from core organizing centres.

Content Validation of Clinician-Reported Items for a Severity Measure for CDKL5 Deficiency Disorder

CDKL5 deficiency disorder (CDD) results in early-onset seizures and severe developmental impairments. A CDD clinical severity assessment (CCSA) was previously developed with clinician and parent-report items to capture information on a range of domains. Consistent with US Food and Drug Administration (FDA) guidelines, content validation is the first step in evaluating the psychometric properties of an outcome measure. The aim of this study was to validate the content of the clinician-reported items in the CCSA (CCSA-Clinician). Eight neurologists leading the USA CDD Center of Excellence clinics were interviewed using the "think aloud" technique to critique 26 clinician-reported items. Common themes were aggregated, and a literature search of related assessments informed item modifications. The clinicians then participated in 2 consensus meetings to review themes and finalize the items. A consensus was achieved for the content of the CCSA-Clinician. Eight of the original items were omitted, 11 items were added, and the remaining 18 items were revised. The final 29 items were classified into 2 domains: functioning and neurologic impairments. This study enabled refinement of the CCSA-Clinician and provided evidence for its content validity. This preliminary validation is essential before field testing and further validation, in order to advance the instrument toward clinical trial readiness.

Human neuropathology confirms projection neuron and interneuron defects and delayed oligodendrocyte production and maturation in FOXG1 syndrome

The Forkhead transcription factor FOXG1 is a prerequisite for telencephalon development in mammals and is an essential factor controlling expansion of the dorsal telencephalon by promoting neuron and interneuron production. Heterozygous FOXG1 gene mutations cause FOXG1 syndrome characterized by severe intellectual disability, motor delay, dyskinetic movements and epilepsy. Neuroimaging studies in patients disclose constant features including microcephaly, corpus callosum dysgenesis and delayed myelination. Currently, investigative research on the underlying pathophysiology relies on mouse models only and indicates that de-repression of FOXG1 target genes may cause premature neuronal differentiation at the expense of the progenitor pool, patterning and migration defects with impaired formation of cortico-cortical projections. It remains an open question to which extent this recapitulates the neurodevelopmental pathophysiology in FOXG1-haploinsufficient patients. To close this gap, we performed neuropathological analyses in two foetal cases with FOXG1 premature stop codon mutations interrupted during the third trimester of the pregnancy for microcephaly and corpus callosum dysgenesis. In these foetuses, we observed cortical lamination defects and decreased neuronal density mainly affecting layers II, III and V that normally give rise to cortico-cortical and inter-hemispheric axonal projections. GABAergic interneurons were also reduced in number in the cortical plate and persisting germinative zones. Additionally, we observed more numerous PDGFRα-positive oligodendrocyte precursor cells and fewer Olig2-positive pre-oligodendrocytes compared to age-matched control brains, arguing for delayed production and differentiation of oligodendrocyte lineage leading to delayed myelination. These findings provide key insights into the human pathophysiology of FOXG1 syndrome.

Nucleocytoplasmic transport of the RNA-binding protein CELF2 regulates neural stem cell fates

The development of the cerebral cortex requires balanced expansion and differentiation of neural stem/progenitor cells (NPCs), which rely on precise regulation of gene expression. Because NPCs often exhibit transcriptional priming of cell-fate-determination genes, the ultimate output of these genes for fate decisions must be carefully controlled in a timely fashion at the post-transcriptional level, but how that is achieved is poorly understood. Here, we report that de novo missense variants in an RNA-binding protein CELF2 cause human cortical malformations and perturb NPC fate decisions in mice by disrupting CELF2 nucleocytoplasmic transport. In self-renewing NPCs, CELF2 resides in the cytoplasm, where it represses mRNAs encoding cell fate regulators and neurodevelopmental disorder-related factors. The translocation of CELF2 into the nucleus releases mRNA for translation and thereby triggers NPC differentiation. Our results reveal that CELF2 translocation between subcellular compartments orchestrates mRNA at the translational level to instruct cell fates in cortical development.

Reviewing Evidence for the Relationship of EEG Abnormalities and RTT Phenotype Paralleled by Insights from Animal Studies

Rett syndrome (RTT) is a rare neurodevelopmental disorder that is usually caused by mutations of the MECP2 gene. Patients with RTT suffer from severe deficits in motor, perceptual and cognitive domains. Electroencephalogram (EEG) has provided useful information to clinicians and scientists, from the very first descriptions of RTT, and yet no reliable neurophysiological biomarkers related to the pathophysiology of the disorder or symptom severity have been identified to date. To identify consistently observed and potentially informative EEG characteristics of RTT pathophysiology, and ascertain areas most worthy of further systematic investigation, here we review the literature for EEG abnormalities reported in patients with RTT and in its disease models. While pointing to some promising potential EEG biomarkers of RTT, our review identify areas of need to realize the potential of EEG including (1) quantitative investigation of promising clinical-EEG observations in RTT, e.g., shift of mu rhythm frequency and EEG during sleep; (2) closer alignment of approaches between patients with RTT and its animal models to strengthen the translational significance of the work (e.g., EEG measurements and behavioral states); (3) establishment of large-scale consortium research, to provide adequate Ns to investigate age and genotype effects.

Defective insulin receptor signaling in hPSCs skews pluripotency and negatively perturbs neural differentiation

Human embryonic stem cells are a type of pluripotent stem cells (hPSCs) that are used to investigate their differentiation into diverse mature cell types for molecular studies. The mechanisms underlying insulin receptor (IR)-mediated signaling in the maintenance of human pluripotent stem cell (hPSC) identity and cell fate specification are not fully understood. Here, we used two independent shRNAs to stably knock down IRs in two hPSC lines that represent pluripotent stem cells and explored the consequences on expression of key proteins in pathways linked to proliferation and differentiation. We consistently observed lowered pAKT in contrast to increased pERK1/2 and a concordant elevation in pluripotency gene expression. ERK2 chromatin immunoprecipitation, luciferase assays, and ERK1/2 inhibitors established direct causality between ERK1/2 and OCT4 expression. Of importance, RNA sequencing analyses indicated a dysregulation of genes involved in cell differentiation and organismal development. Mass spectrometry–based proteomic analyses further confirmed a global downregulation of extracellular matrix proteins. Subsequent differentiation toward the neural lineage reflected alterations in SOX1⁺PAX6⁺ neuroectoderm and FOXG1⁺ cortical neuron marker expression and protein localization. Collectively, our data underscore the role of IR-mediated signaling in maintaining pluripotency, the extracellular matrix necessary for the stem cell niche, and regulating cell fate specification including the neural lineage.

Network for Therapy in Rare Epilepsies (NETRE): Lessons From the Past 15 Years

Background: In 2005, Network for Therapy in Rare Epilepsies (NETRE)-was initiated in order to share treatment experiences among clinicians in patients with rare epilepsies. Here we describe the structure of the rapidly growing NETRE and summarize some of the findings of the last 15 years. Methodology/Structure of NETRE: NETRE is organized in distinct groups (currently >270). Starting point is always a patient with a rare epilepsy/ epileptic disorder. This creates a new group, and next, a medical coordinator is appointed. The exchange of experiences is established using a data entry form, which the coordinator sends to colleagues. The primary aim is to exchange experiences (retrospectively, anonymously, MRI results also non-anonymously) of the epilepsy treatment as well as on clinical presentation and comorbidities NETRE is neither financed nor sponsored. Results: Some of the relevant results: (1) first description of FIRES as a new epilepsy syndrome and its further investigation, (2) in SCN2A, the assignment to gain- vs. loss-of-function mutations has a major impact on clinical decisions to use or avoid treatment with sodium channel blockers, (3) the important aspect of avoiding overtreatment in CDKL5 patients, due to loss of effects of anticonvulsants after 12 months, (4) pathognomonic MRI findings in FOXG1 patients, (5) the first description of pathognomonic chewing-induced seizures in SYNGAP1 patients, and the therapeutic effect of statins as anticonvulsant in these patients, (6) the phenomenon of another reflex epilepsy-bathing epilepsy associated with a SYN1 mutation. Of special interest is also a NETRE group following twins with genetic and/or structural epilepsies [including vanishing-twin-syndrome and twin-twin-transfusion syndrome) [= "Early Neuroimpaired Twin Entity" (ENITE)]. Discussion and Perspective: NETRE enables clinicians to quickly exchange information on therapeutic experiences in rare diseases with colleagues at an international level. For both parents and clinicians/scientist this international exchange is both reassuring and helpful. In collaboration with other groups, personalized therapeutic approaches are sought, but the present limitations of currently available therapies are also highlighted. Presently, the PATRE Project (PATient based phenotyping and evaluation of therapy for Rare Epilepsies) is commencing, in which information on therapies will be obtained directly from patients and their caregivers.

IQSEC2 disorder: A new disease entity or a Rett spectrum continuum?

IQSEC2 mutations are associated with IQSEC2-related intellectual disability (ID). Phenotypic spectrum has been better defined in the last few years by the increasing number of reported cases although the genotype-phenotype relationship for IQSEC2 remains overall complex. As for IQSEC2-related ID a wide phenotypic diversity has been described in Rett syndrome (RTT). Several patients harboring IQSEC2 mutations present with clinical symptoms similar to RTT and some cases meet most of the criteria for classic RTT. With the aim of establishing a genotype-phenotype correlation, we collected data of 16 patients harboring IQSEC2 point mutations (15 of them previously unreported) and of five novel patients carrying CNVs encompassing IQSEC2. Most of our patients surprisingly shared a moderate-to-mild phenotype. The similarities in the clinical course between our mild cases and patients with milder forms of atypical RTT reinforce the hypothesis that also IQSEC2 mutated patients may lay under the wide clinical spectrum of RTT and thus IQSEC2 should be considered in the differential diagnosis. Our data confirm that position, type of variant and gender are crucial for IQSEC2-associated phenotype delineation.

Linkage analysis identifies an isolated strabismus locus at 14q12 overlapping with FOXG1 syndrome region

Strabismus is a common condition, affecting 1%–4% of individuals. Isolated strabismus has been studied in families with Mendelian inheritance patterns. Despite the identification of multiple loci via linkage analyses, no specific genes have been identified from these studies. The current study is based on a seven-generation family with isolated strabismus inherited in an autosomal dominant manner. A total of 13 individuals from a common ancestor have been included for linkage analysis. Among these, nine are affected and four are unaffected. A single linkage signal has been identified at an 8.5 Mb region of chromosome 14q12 with a multipoint LOD (logarithm of the odds) score of 4.69. Disruption of this locus is known to cause FOXG1 syndrome (or congenital Rett syndrome; OMIM #613454 and *164874), in which 84% of affected individuals present with strabismus. With the incorporation of next-generation sequencing and in-depth bioinformatic analyses, a 4 bp non-coding deletion was prioritised as the top candidate for the observed strabismus phenotype. The deletion is predicted to disrupt regulation of FOXG1, which encodes a transcription factor of the Forkhead family. Suggestive of an autoregulation effect, the disrupted sequence matches the consensus FOXG1 and Forkhead family transcription factor binding site and has been observed in previous ChIP-seq studies to be bound by Foxg1 in early mouse brain development. Future study of this specific deletion may shed light on the regulation of FOXG1 expression and may enhance our understanding of the mechanisms contributing to strabismus and FOXG1 syndrome.

The generation of an induced pluripotent stem cell line (DCGi001-A) from an individual with FOXG1 syndrome carrying the c.460dupG (p.Glu154fs) variation in the FOXG1 gene

FOXG1 syndrome is a neurodevelopmental disorder caused by mutations in the FOXG1 gene. Here, an induced pluripotent stem cell (iPSC) line was generated from human dermal fibroblasts of an individual with the c.490dupG (p.Glu154fs) mutation in the FOXG1 gene. Fibroblasts were reprogrammed using non-integrating episomal plasmids and pluripotency marker expression was confirmed by both immunocytochemistry and quantitative PCR in the resultant iPSC line. There were no karyotypic abnormalities and the cell line successfully differentiated into all three germ layers. This cell line may prove useful in the study of the pathogenic mechanisms that underpin FOXG1 syndrome.

Structural Basis for DNA Recognition by FOXG1 and the Characterization of Disease-causing FOXG1 Mutations

Forkhead box G1 (FOXG1) is a transcription factor mainly expressed in the brain that plays a critical role in the development and regionalization of the forebrain. Aberrant expression of FOXG1 has implications in FOXG1 syndrome, a serious neurodevelopmental disorder. Here, we report the crystal structure of the FOXG1 DNA-binding domain (DBD) in complex with the forkhead consensus DNA site DBE2 at the resolution of 1.6 Å. FOXG1-DBD adopts a typical winged helix fold. Compared to those of other FOX-DBD/DBE2 structures, the N terminus, H3 helix and wing2 region of FOXG1-DBD exhibit differences in DNA recognition. The FOXG1-DBD wing2 region adopts a unique architecture composed of two β-strands that differs from all other known FOX-DBD wing2 folds. Mutation assays revealed that the disease-causing mutations within the FOXG1-DBD affect DNA binding, protein thermal stability, or both. Our report provides initial insight into how FOXG1 binds DNA and sheds light on how disease-causing mutations in FOXG1-DBD affect its DNA-binding ability.

Expansion of the phenotypic spectrum of de novo missense variants in kinesin family member 1A (KIF1A)

Defects in the motor domain of kinesin family member 1A (KIF1A), a neuron-specific ATP-dependent anterograde axonal transporter of synaptic cargo, are well-recognized to cause a spectrum of neurological conditions, commonly known as KIF1A-associated neurological disorders (KAND). Here, we report one mutation-negative female with classic Rett syndrome (RTT) harboring a de novo heterozygous novel variant [NP_001230937.1:p.(Asp248Glu)] in the highly conserved motor domain of KIF1A. In addition, three individuals with severe neurodevelopmental disorder along with clinical features overlapping with KAND are also reported carrying de novo heterozygous novel [NP_001230937.1:p.(Cys92Arg) and p.(Pro305Leu)] or previously reported [NP_001230937.1:p.(Thr99Met)] variants in KIF1A. In silico tools predicted these variants to be likely pathogenic, and 3D molecular modeling predicted defective ATP hydrolysis and/or microtubule binding. Using the neurite tip accumulation assay, we demonstrated that all novel KIF1A variants significantly reduced the ability of the motor domain of KIF1A to accumulate along the neurite lengths of differentiated SH-SY5Y cells. In vitro microtubule gliding assays showed significantly reduced velocities for the variant p.(Asp248Glu) and reduced microtubule binding for the p.(Cys92Arg) and p.(Pro305Leu) variants, suggesting a decreased ability of KIF1A to move along microtubules. Thus, this study further expanded the phenotypic characteristics of KAND individuals with pathogenic variants in the KIF1A motor domain to include clinical features commonly seen in RTT individuals.

Diagnosis of FOXG1 syndrome caused by recurrent balanced chromosomal rearrangements: case study and literature review

Background

The FOXG1 gene plays a vital role in mammalian brain differentiation and development. Intra- and intergenic mutations resulting in loss of function or altered expression of the FOXG1 gene cause FOXG1 syndrome. The hallmarks of this syndrome are severe developmental delay with absent verbal language, post-natal growth restriction, post-natal microcephaly, and a recognizable movement disorder characterized by chorea and dystonia.

Case presentation

Here we describe a case of a 7-year-old male patient found to have a de novo balanced translocation between chromosome 3 at band 3q14.1 and chromosome 14 at band 14q12 via G-banding chromosome and Fluorescence In Situ Hybridization (FISH) analyses. This rearrangement disrupts the proximity of FOXG1 to a previously described smallest region of deletion overlap (SRO), likely resulting in haploinsufficiency.

Conclusions

This case adds to the growing body of literature implicating chromosomal structural variants in the manifestation of this disorder and highlights the vital role of cis-acting regulatory elements in the normal expression of this gene. Finally, we propose a protocol for reflex FISH analysis to improve diagnostic efficiency for patients with suspected FOXG1 syndrome.

Comparison of Core Features in Four Developmental Encephalopathies in the Rett Natural History Study

OBJECTIVE

Rett syndrome, CDKL5-deficiency disorder, FOXG1 disorder, and MECP2 duplication disorder are developmental encephalopathies with shared and distinct features. Although they are historically linked, no direct comparison has been performed. The first head-to-head comparison of clinical features in these conditions is presented.

METHODS

Comprehensive clinical information was collected from 793 individuals enrolled in the Rett and Rett-Related Disorders Natural History Study. Clinical features including clinical severity, regression, and seizures were cross-sectionally compared between diagnoses to test the hypothesis that these are 4 distinct disorders.

RESULTS

Distinct patterns of clinical severity, seizure onset age, and regression were present. Individuals with CDKL5-deficency disorder were the most severely affected and had the youngest age at seizure onset (2 months), whereas children with MECP2 duplication syndrome had the oldest median age at seizure onset (64 months) and lowest severity scores. Rett syndrome and FOGX1 were intermediate in both features. Smaller head circumference correlates with increased severity in all disorders and earlier age at seizure onset in MECP2 duplication syndrome. Developmental regression occurred in all Rett syndrome participants (median = 18 months) but only 23 to 34% of the other disorders. Seizure incidence prior to the baseline visit was highest for CDKL5 deficiency disorder (96.2%) and lowest for Rett syndrome (47.5%). Other clinical features including seizure types and frequency differed among groups.

INTERPRETATION

Although these developmental encephalopathies share many clinical features, clear differences in severity, regression, and seizures warrant considering them as unique disorders. These results will aid in the development of disease-specific severity scales, precise therapeutics, and future clinical trials. ANN NEUROL 2020;88:396-406.

Application of CRISPR/Cas9 to human-induced pluripotent stem cells: from gene editing to drug discovery

Human-induced pluripotent stem cells (hiPSCs) and CRISPR/Cas9 gene editing system represent two instruments of basic and translational research, which both allow to acquire deep insight about the molecular bases of many diseases but also to develop pharmacological research.This review is focused to draw up the latest technique of gene editing applied on hiPSCs, exploiting some of the genetic manipulation directed to the discovery of innovative therapeutic strategies. There are many expediencies provided by the use of hiPSCs, which can represent a disease model clinically relevant and predictive, with a great potential if associated to CRISPR/Cas9 technology, a gene editing tool powered by ease and precision never seen before.Here, we describe the possible applications of CRISPR/Cas9 to hiPSCs: from drug development to drug screening and from gene therapy to the induction of the immunological response to specific virus infection, such as HIV and SARS-Cov-2.

Foxg1 Upregulation Enhances Neocortical Activity

Foxg1 is an ancient transcription factor gene orchestrating a number of neurodevelopmental processes taking place in the rostral brain. In this study, we investigated its impact on neocortical activity. We found that mice overexpressing Foxg1 in neocortical pyramidal cells displayed an electroencephalography (EEG) with increased spike frequency and were more prone to kainic acid (KA)-induced seizures. Consistently, primary cultures of neocortical neurons gain-of-function for Foxg1 were hyperactive and hypersynchronized. That reflected an unbalanced expression of key genes encoding for ion channels, gamma aminobutyric acid and glutamate receptors, and was likely exacerbated by a pronounced interneuron depletion. We also detected a transient Foxg1 upregulation ignited in turn by neuronal activity and mediated by immediate early genes. Based on this, we propose that even small changes of Foxg1 levels may result in a profound impact on pyramidal cell activity, an issue relevant to neuronal physiology and neurological aberrancies associated to FOXG1 copy number variations.