Novel FOXG1 mutations associated with the congenital variant of Rett syndrome

Genomic analysis in Chilean patients with suspected Rett syndrome: keep a broad differential diagnosis

Introduction: Rett syndrome (RTT, MIM #312750) is a rare genetic disorder that leads to developmental regression and severe disability and is caused by pathogenic variants in the MECP2 gene. The diagnosis of RTT is based on clinical features and, depending on resources and access, on molecular confirmation. There is scarce information on molecular diagnosis from patients in Latin America, mostly due to limited availability and coverage of genomic testing. This pilot study aimed to implement genomic testing and characterize clinical and molecular findings in a group of Chilean patients with a clinical diagnosis of RTT. Methods: Twenty-eight patients with suspected RTT underwent characterization of phenotypic manifestations and molecular testing using Clinical Exome SolutionTM CES_V2 by SOPHiA Genetics. Data was analyzed using the commercial bioinformatics platform, SOPHiA DDMTM. A virtual panel of 34 genes, including MECP2 and other genes that are in the differential diagnosis of RTT, was used to prioritize initial analyses, followed by evaluation of the complete exome sequence data. Results: Twelve patients (42.8% of participants) had variants in MECP2, of which 11 (39.2%) were interpreted as pathogenic/likely pathogenic (P/LP), thus confirming the diagnosis of RTT in them. Eight additional patients (28.5%) harbored ten variants in nine other genes. Four of these variants were interpreted as P/LP (14.2%) (GRIN2B, MADD, TRPM3 and ZEB2) resulting in alternative neurodevelopmental diagnoses, and six were considered of uncertain significance. No evident candidate variant was found for eight patients. Discussion: This study allowed to reach a diagnosis in half of the participants. The diagnosis of RTT was confirmed in over a third of them, while others were found to have alternative neurodevelopmental disorders. Further evaluation is needed to identify the cause in those with negative or uncertain results. This information is useful for the patients, families, and clinicians to guide clinical management, even more so since the development of novel therapies for RTT. We also show the feasibility of implementing a step-wide approach to genomic testing in a setting with limited resources.

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.

The role of insulin/IGF1 signalling in neurodevelopmental and neuropsychiatric disorders - Evidence from human neuronal cell models

Insulin and insulin-like growth factor 1 (IGF1) signalling play a central role in the development and maintenance of neurons in the brain, and human neurodevelopmental as well as neuropsychiatric disorders have been linked to impaired insulin and IGF1 signalling. This review focuses on the impairments of the insulin and IGF1 signalling cascade in the context of neurodevelopmental and neuropsychiatric disorders, based on evidence from human neuronal cell models. Clear evidence was obtained for impaired insulin and IGF1 receptor downstream signalling in neurodevelopmental disorders, while the evidence for its role in neuropsychiatric disorders was less substantial. Human neuronal model systems can greatly add to our knowledge about insulin/IGF1 signalling in the brain, its role in restoring dendritic maturity, and complement results from clinical studies and animal models. Moreover, they represent a useful model for the development of new therapeutic strategies. Further research is needed to systematically investigate the exact role of the insulin/IGF1 signalling cascades in neurodevelopmental and neuropsychiatric disorders, and to elucidate the respective therapeutic implications.

Expanding genotype-phenotype correlations in FOXG1 syndrome: results from a patient registry

BACKGROUND

We refine the clinical spectrum of FOXG1 syndrome and expand genotype-phenotype correlations through evaluation of 122 individuals enrolled in an international patient registry.

METHODS

The FOXG1 syndrome online patient registry allows for remote collection of caregiver-reported outcomes. Inclusion required documentation of a (likely) pathogenic variant in FOXG1. Caregivers were administered a questionnaire to evaluate clinical severity of core features of FOXG1 syndrome. Genotype-phenotype correlations were determined using nonparametric analyses.

RESULTS

We studied 122 registry participants with FOXG1 syndrome, aged < 12 months to 24 years. Caregivers described delayed or absent developmental milestone attainment, seizures (61%), and movement disorders (58%). Participants harbouring a missense variant had a milder phenotype. Compared to individuals with gene deletions (0%) or nonsense variants (20%), missense variants were associated with more frequent attainment of sitting (73%). Further, individuals with missense variants (41%) achieved independent walking more frequently than those with gene deletions (0%) or frameshift variants (6%). Presence of epilepsy also varied by genotype and was significantly more common in those with gene deletions (81%) compared to missense variants (47%). Individuals with gene deletions were more likely to have higher seizure burden than other genotypes with 53% reporting daily seizures, even at best control. We also observed that truncations preserving the forkhead DNA binding domain were associated with better developmental outcomes.

CONCLUSION

We refine the phenotypic spectrum of neurodevelopmental features associated with FOXG1 syndrome. We strengthen genotype-driven outcomes, where missense variants are associated with a milder clinical course.

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.

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.

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.

Technological Improvements in the Genetic Diagnosis of Rett Syndrome Spectrum Disorders

Rett syndrome (RTT) is a severe neurodevelopmental disorder that constitutes the second most common cause of intellectual disability in females worldwide. In the past few years, the advancements in genetic diagnosis brought by next generation sequencing (NGS), have made it possible to identify more than 90 causative genes for RTT and significantly overlapping phenotypes (RTT spectrum disorders). Therefore, the clinical entity known as RTT is evolving towards a spectrum of overlapping phenotypes with great genetic heterogeneity. Hence, simultaneous multiple gene testing and thorough phenotypic characterization are mandatory to achieve a fast and accurate genetic diagnosis. In this review, we revise the evolution of the diagnostic process of RTT spectrum disorders in the past decades, and we discuss the effectiveness of state-of-the-art genetic testing options, such as clinical exome sequencing and whole exome sequencing. Moreover, we introduce recent technological advancements that will very soon contribute to the increase in diagnostic yield in patients with RTT spectrum disorders. Techniques such as whole genome sequencing, integration of data from several “omics”, and mosaicism assessment will provide the tools for the detection and interpretation of genomic variants that will not only increase the diagnostic yield but also widen knowledge about the pathophysiology of these disorders.

FOXG1 Gene and Its Related Phenotypes

FOXG1 is an important transcriptional repressor found in cell precursor of the ventricular region and in neurons in the early stage of differentiation during the development of the nervous epithelium in the cerebrum and optical formation. Mutations involving FOXG1 gene have been described first in subjects with congenital Rett syndrome. They can cause seizure, delayed psychomotor development, language disorders, and autism. FOXG1 deletions or intragenic mutations also determinate reduction in head circumference, structural defects in the corpus callosum, abnormal movements, especially choreiform, and intellectual retardation with no speech. Patients with duplications of 14q12 present infantile spasms and have subsequent intellectual disability with autistic features, head circumference in the normal range, and regular aspect of corpus callosum. Clinical characteristics of patients with FOXG1 variants include growth deficit after birth associated with microcephaly, facial dysmorphisms, important delay with no language, deficit in social interaction like autism, sleep disorders, stereotypes, including dyskinesia, and seizures. In these patients, it is not characteristic a history of loss of acquired skills.

Genetic diagnoses in pediatric patients with epilepsy and comorbid intellectual disability

PURPOSE

The aim of this retrospective study is to investigate the genetic etiology and propose a diagnostic strategy for pediatric patients with epilepsy and comorbid intellectual disability (ID).

METHODS

From September 2014 to May 2020, a total of 102 pediatric patients diagnosed with epilepsy with co-morbid ID with unknown causes were included in this study. All patients underwent tests of single nucleotide polymorphism (SNP) array for chromosomal abnormalities. Whole exome sequencing (WES) was consecutively performed in patients without diagnostic copy number variants (CNVs) (n = 85) for single nucleotide variants (SNVs). Subgroup analyses based on the age of seizure onset and ID severity were done.

RESULTS

The overall diagnostic yield of genetic aberrations was 33.3 % (34/102), which comprised 50.0 % with diagnostic CNVs and 50.0 % with diagnostic SNVs. The yield nominally increased with ID severity and decreased with age of seizure onset, though this result was not statistically significant. The diagnostic yield of SNVs in patients with seizure onset in the first year of life (25.0 % (11/44)) was significantly higher than those with childhood-onset epilepsy (10.3 % (6/58)) (p = 0.049), however, the diagnostic yield of CNVs in patients with childhood-onset epilepsy (17.2 % (10/58) was higher than the diagnostic yield of SNVs (10.3 % (6/58)). The most frequently syndromic epilepsy detected by SNP array was Angelman syndrome (n=4), including one confirmed with paternal uniparental disomy. Meanwhile, the most frequent SNVs were mutations of MECP2 (n=2) and IQSEC2 (n = 2) in sporadic cases.

CONCLUSION

Both CMA and WES are advantageous as unbiased approaches for a genetically heterogeneous condition. We proposed an effective diagnostic strategy for pediatric patients with epilepsy. For patients with seizure onset in the first year of life, WES is recommended as the first-tier test. However, for patients with childhood-onset epilepsy, SNP array should be considered for the first-tier test.

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.

Neurodevelopmental impairment induced by prenatal valproic acid exposure shown with the human cortical organoid-on-a-chip model

Prenatal exposure to environmental insults can increase the risk of developing neurodevelopmental disorders. Administration of the antiepileptic drug valproic acid (VPA) during pregnancy is tightly associated with a high risk of neurological disorders in offspring. However, the lack of an ideal human model hinders our comprehensive understanding of the impact of VPA exposure on fetal brain development, especially in early gestation. Herein, we present the first report indicating the effects of VPA on brain development at early stages using engineered cortical organoids from human induced pluripotent stem cells (hiPSCs). Cortical organoids were generated on micropillar arrays in a controlled manner, recapitulating the critical features of human brain development during early gestation. With VPA exposure, cortical organoids exhibited neurodevelopmental dysfunction characterized by increased neuron progenitors, inhibited neuronal differentiation and altered forebrain regionalization. Transcriptome analysis showed new markedly altered genes (e.g., KLHL1, LHX9, and MGARP) and a large number of differential expression genes (DEGs), some of which are related to autism. In particular, comparison of transcriptome data via GSEA and correlation analysis revealed the high similarity between VPA-exposed organoids with the postmortem ASD brain and autism patient-derived organoids, implying the high risk of autism with prenatal VPA exposure, even in early gestation. These new findings facilitate a better understanding of the cellular and molecular mechanisms underlying postnatal brain disorders (such as autism) with prenatal VPA exposure. This established cortical organoid-on-a-chip platform is valuable for probing neurodevelopmental disorders under environmental exposure and can be extended to applications in the study of diseases and drug testing.

A case of congenital Rett variant in a Chinese patient caused by a FOXG1 mutation

Rett syndrome (RTT) is a severe progressive neurodevelopmental disease characterized by psychomotor regression. The FOXG1 gene is one of the pathogenic genes associated with the congenital Rett variant, which is less studied. Only a few Chinese patients with FOXG1 mutation have been reported. In this study, we describe a Chinese female patient with congenital Rett variant who presented with psycho-motor retardation, developmental regression, microcephaly, seizure, stereotypic hand movement and hypotonia. Targeted high-throughput sequencing was conducted, and a heterozygous FOXG1 mutation [NM_005249.4: c.506dupG (P.G169Gfs* 286)] was identified. It was a frameshift mutation resulting in alteration of the reading frames downstream of the mutation. SIMILAR CASES PUBLISHED: 10. CONFLICT OF INTEREST: None.

Transcription and Beyond: Delineating FOXG1 Function in Cortical Development and Disorders

Forkhead Box G1 (FOXG1) is a member of the Forkhead family of genes with non-redundant roles in brain development, where alteration of this gene's expression significantly affects the formation and function of the mammalian cerebral cortex. FOXG1 haploinsufficiency in humans is associated with prominent differences in brain size and impaired intellectual development noticeable in early childhood, while homozygous mutations are typically fatal. As such, FOXG1 has been implicated in a wide spectrum of congenital brain disorders, including the congenital variant of Rett syndrome, infantile spasms, microcephaly, autism spectrum disorder (ASD) and schizophrenia. Recent technological advances have yielded greater insight into phenotypic variations observed in FOXG1 syndrome, molecular mechanisms underlying pathogenesis of the disease, and multifaceted roles of FOXG1 expression. In this review, we explore the emerging mechanisms of FOXG1 in a range of transcriptional to posttranscriptional events in order to evolve our current view of how a single transcription factor governs the assembly of an elaborate cortical circuit responsible for higher cognitive functions and neurological disorders.

FOXG1-Related Syndrome: From Clinical to Molecular Genetics and Pathogenic Mechanisms

Individuals with mutations in forkhead box G1 (FOXG1) belong to a distinct clinical entity, termed “FOXG1-related encephalopathy”. There are two clinical phenotypes/syndromes identified in FOXG1-related encephalopathy, duplications and deletions/intragenic mutations. In children with deletions or intragenic mutations of FOXG1, the recognized clinical features include microcephaly, developmental delay, severe cognitive disabilities, early-onset dyskinesia and hyperkinetic movements, stereotypies, epilepsy, and cerebral malformation. In contrast, children with duplications of FOXG1 are typically normocephalic and have normal brain magnetic resonance imaging. They also have different clinical characteristics in terms of epilepsy, movement disorders, and neurodevelopment compared with children with deletions or intragenic mutations. FOXG1 is a transcriptional factor. It is expressed mainly in the telencephalon and plays a pleiotropic role in the development of the brain. It is a key player in development and territorial specification of the anterior brain. In addition, it maintains the expansion of the neural proliferating pool, and also regulates the pace of neocortical neuronogenic progression. It also facilitates cortical layer and corpus callosum formation. Furthermore, it promotes dendrite elongation and maintains neural plasticity, including dendritic arborization and spine densities in mature neurons. In this review, we summarize the clinical features, molecular genetics, and possible pathogenesis of FOXG1-related syndrome.

Microduplication of Xp22.31 and MECP2 Pathogenic Variant in a Girl with Rett Syndrome: A Case Report

Rett syndrome (RS) is a neurodevelopmental infantile disease characterized by an early normal psychomotor development followed by a regression in the acquisition of normal developmental stages. In the majority of cases, it leads to a sporadic mutation in the MECP2 gene, which is located on the X chromosome. However, this syndrome has also been associated with microdeletions, gene translocations, and other gene mutations. A 12-year-old female Colombian patient was presented with refractory epilepsy and regression in skill acquisition (especially language with motor and verbal stereotypies, hyperactivity, and autistic spectrum disorder criteria). The patient was born to non-consanguineous parents and had an early normal development until the age of 36 months. Comparative genomic hybridization array-CGH (750K) was performed and Xp22.31 duplication was detected (6866889-8115153) with a size of 1.248 Mb associated with developmental delay, epilepsy, and autistic traits. Given the clinical criteria of RS, MECP2 sequencing was performed which showed a de novo pathogenic variant c.338C>G (p.Pro113Arg). The features of RS include intellectual disability, developmental delay, and autism. These features are associated with copy number variations (CNVs) on the X chromosome (Xp22.31 microduplication). Here we present the first reported case of simultaneous CNV and MECP2 pathogenic mutation in a patient with RS. We propose that both DNA alterations might have a synergistic effect and could lead to variable expressivity of the phenotype.

Cortical Seizures in FoxG1+/- Mice are Accompanied by Akt/S6 Overactivation, Excitation/Inhibition Imbalance and Impaired Synaptic Transmission

The correct morphofunctional shaping of the cerebral cortex requires a continuous interaction between intrinsic (genes/molecules expressed within the tissue) and extrinsic (e.g., neural activity) factors at all developmental stages. Forkhead Box G1 (FOXG1) is an evolutionarily conserved transcription factor, essential for the cerebral cortex patterning and layering. FOXG1-related disorders, including the congenital form of Rett syndrome, can be caused by deletions, intragenic mutations or duplications. These genetic alterations are associated with a complex phenotypic spectrum, spanning from intellectual disability, microcephaly, to autistic features, and epilepsy. We investigated the functional correlates of dysregulated gene expression by performing electrophysiological assays on FoxG1^+/- mice. Local Field Potential (LFP) recordings on freely moving animals detected cortical hyperexcitability. On the other hand, patch-clamp recordings showed a downregulation of spontaneous glutamatergic transmission. These findings were accompanied by overactivation of Akt/S6 signaling. Furthermore, the expression of vesicular glutamate transporter 2 (vGluT2) was increased, whereas the level of the potassium/chloride cotransporter KCC2 was reduced, thus indicating a higher excitation/inhibition ratio. Our findings provide evidence that altered expression of a key gene for cortical development can result in specific alterations in neural circuit function at the macro- and micro-scale, along with dysregulated intracellular signaling and expression of proteins controlling circuit excitability.

X chromosome inactivation does not necessarily determine the severity of the phenotype in Rett syndrome patients

Rett syndrome (RTT) is a severe neurological disorder usually caused by mutations in the MECP2 gene. Since the MECP2 gene is located on the X chromosome, X chromosome inactivation (XCI) could play a role in the wide range of phenotypic variation of RTT patients; however, classical methylation-based protocols to evaluate XCI could not determine whether the preferentially inactivated X chromosome carried the mutant or the wild-type allele. Therefore, we developed an allele-specific methylation-based assay to evaluate methylation at the loci of several recurrent MECP2 mutations. We analyzed the XCI patterns in the blood of 174 RTT patients, but we did not find a clear correlation between XCI and the clinical presentation. We also compared XCI in blood and brain cortex samples of two patients and found differences between XCI patterns in these tissues. However, RTT mainly being a neurological disease complicates the establishment of a correlation between the XCI in blood and the clinical presentation of the patients. Furthermore, we analyzed MECP2 transcript levels and found differences from the expected levels according to XCI. Many factors other than XCI could affect the RTT phenotype, which in combination could influence the clinical presentation of RTT patients to a greater extent than slight variations in the XCI pattern.

Structural brain anomalies in patients with FOXG1 syndrome and in Foxg1+/- mice

Objective

FOXG1 syndrome is a rare neurodevelopmental disorder associated with heterozygous FOXG1 variants or chromosomal microaberrations in 14q12. The study aimed at assessing the scope of structural cerebral anomalies revealed by neuroimaging to delineate the genotype and neuroimaging phenotype associations.

Methods

We compiled 34 patients with a heterozygous (likely) pathogenic FOXG1 variant. Qualitative assessment of cerebral anomalies was performed by standardized re-analysis of all 34 MRI data sets. Statistical analysis of genetic, clinical and neuroimaging data were performed. We quantified clinical and neuroimaging phenotypes using severity scores. Telencephalic phenotypes of adult Foxg1+/- mice were examined using immunohistological stainings followed by quantitative evaluation of structural anomalies.

Results

Characteristic neuroimaging features included corpus callosum anomalies (82%), thickening of the fornix (74%), simplified gyral pattern (56%), enlargement of inner CSF spaces (44%), hypoplasia of basal ganglia (38%), and hypoplasia of frontal lobes (29%). We observed a marked, filiform thinning of the rostrum as recurrent highly typical pattern of corpus callosum anomaly in combination with distinct thickening of the fornix as a characteristic feature. Thickening of the fornices was not reported previously in FOXG1 syndrome. Simplified gyral pattern occurred significantly more frequently in patients with early truncating variants. Higher clinical severity scores were significantly associated with higher neuroimaging severity scores. Modeling of Foxg1 heterozygosity in mouse brain recapitulated the associated abnormal cerebral morphology phenotypes, including the striking enlargement of the fornix.

Interpretation

Combination of specific corpus callosum anomalies with simplified gyral pattern and hyperplasia of the fornices is highly characteristic for FOXG1 syndrome.

De novo mosaic MECP2 mutation in a female with Rett syndrome

We describe a female with Rett syndrome carrying a rare de novo mosaic nonsense mutation on MECP2 gene, with random X-chromosome inactivation. Rett syndrome severity in females depends on mosaicism level and tissue specificity, X-chromosome inactivation, epigenetics and environment. Rett syndrome should be considered in both males and females.

FOXG1 Dose in Brain Development

Brain development is a highly regulated process that involves the precise spatio-temporal activation of cell signaling cues. Transcription factors play an integral role in this process by relaying information from external signaling cues to the genome. The transcription factor Forkhead box G1 (FOXG1) is expressed in the developing nervous system with a critical role in forebrain development. Altered dosage of FOXG1 due to deletions, duplications, or functional gain- or loss-of-function mutations, leads to a complex array of cellular effects with important consequences for human disease including neurodevelopmental disorders. Here, we review studies in multiple species and cell models where FOXG1 dose is altered. We argue against a linear, symmetrical relationship between FOXG1 dosage states, although FOXG1 levels at the right time and place need to be carefully regulated. Neurodevelopmental disease states caused by mutations in FOXG1 may therefore be regulated through different mechanisms.

Delineating FOXG1 syndrome: From congenital microcephaly to hyperkinetic encephalopathy

Objective

To provide new insights into the FOXG1-related clinical and imaging phenotypes and refine the phenotype-genotype correlation in FOXG1 syndrome.

Methods

We analyzed the clinical and imaging phenotypes of a cohort of 45 patients with a pathogenic or likely pathogenic FOXG1 variant and performed phenotype-genotype correlations.

Results

A total of 37 FOXG1 different heterozygous mutations were identified, of which 18 are novel. We described a broad spectrum of neurodevelopmental phenotypes, characterized by severe postnatal microcephaly and developmental delay accompanied by a hyperkinetic movement disorder, stereotypes and sleep disorders, and epileptic seizures. Our data highlighted 3 patterns of gyration, including frontal pachygyria in younger patients (26.7%), moderate simplified gyration (24.4%) and mildly simplified or normal gyration (48.9%), corpus callosum hypogenesis mostly in its frontal part, combined with moderate-to-severe myelination delay that improved and normalized with age. Frameshift and nonsense mutations in the N-terminus of FOXG1, which are the most common mutation types, show the most severe clinical features and MRI anomalies. However, patients with recurrent frameshift mutations c.460dupG and c.256dupC had variable clinical and imaging presentations.

Conclusions

These findings have implications for genetic counseling, providing evidence that N-terminal mutations and large deletions lead to more severe FOXG1 syndrome, although genotype-phenotype correlations are not necessarily straightforward in recurrent mutations. Together, these analyses support the view that FOXG1 syndrome is a specific disorder characterized by frontal pachygyria and delayed myelination in its most severe form and hypogenetic corpus callosum in its milder form.

Rett syndrome: a neurological disorder with metabolic components

Rett syndrome (RTT) is a neurological disorder caused by mutations in the X-linked gene methyl-CpG-binding protein 2 (MECP2), a ubiquitously expressed transcriptional regulator. Despite remarkable scientific progress since its discovery, the mechanism by which MECP2 mutations cause RTT symptoms is largely unknown. Consequently, treatment options for patients are currently limited and centred on symptom relief. Thought to be an entirely neurological disorder, RTT research has focused on the role of MECP2 in the central nervous system. However, the variety of phenotypes identified in Mecp2 mutant mouse models and RTT patients implicate important roles for MeCP2 in peripheral systems. Here, we review the history of RTT, highlighting breakthroughs in the field that have led us to present day. We explore the current evidence supporting metabolic dysfunction as a component of RTT, presenting recent studies that have revealed perturbed lipid metabolism in the brain and peripheral tissues of mouse models and patients. Such findings may have an impact on the quality of life of RTT patients as both dietary and drug intervention can alter lipid metabolism. Ultimately, we conclude that a thorough knowledge of MeCP2's varied functional targets in the brain and body will be required to treat this complex syndrome.

Hypoplastic hippocampus in atypical Rett syndrome with a novel FOXG1 mutation

The forkhead box G1 (FOXG1) gene encodes a brain-specific transcription factor and is associated with a congenital variant of atypical Rett syndrome (RTT); several FOXG1 mutations have been identified. The congenital variant of RTT shows a hypoplastic corpus callosum, delayed myelination, and frontal and temporal atrophy. Although no report has described a hippocampal abnormality in humans, the current study suggests that FOXG1 also regulates neurogenesis in the postnatal hippocampus. In the present case, severe developmental delay was observed in a patient with a congenital variant of RTT from about 4months, in conjunction with acquired microcephaly, hypotonia, limited motor function, absent purposeful hand use, and repetitive jerky movements of the upper limbs. A novel missense mutation was identified in FOXG1 on gene analysis (c. 569T>A, p. Ile190Asn). The patient showed not only the typical cerebral abnormalities of a congenital variant of RTT, but also a hypoplastic hippocampus. This novel mutation and cerebral findings may provide new insights into the pathophysiology of the congenital variant of RTT.

Regulatory variants of FOXG1 in the context of its topological domain organisation

FOXG1 syndrome is caused by FOXG1 intragenic point mutations, or by long-range position effects (LRPE) of intergenic structural variants. However, the size of the FOXG1 regulatory landscape is uncertain, because the associated topologically associating domain (TAD) in fibroblasts is split into two domains in embryonic stem cells (hESC). Indeed, it has been suggested that the pathogenetic mechanism of deletions that remove the stem-cell-specific TAD boundary may be enhancer adoption due to ectopic activity of enhancer(s) located in the distal hESC-TAD. Herein we map three de novo translocation breakpoints to the proximal regulatory domain of FOXG1. The classical FOXG1 syndrome in these and in other translocation patients, and in a patient with an intergenic deletion that removes the hESC-specific TAD boundary, do not support the hypothesised enhancer adoption as a main contributor to the FOXG1 syndrome. Also, virtual 4 C and HiC-interaction data suggest that the hESC-specific TAD boundary may not be critical for FOXG1 regulation in a majority of human cells and tissues, including brain tissues and a neuronal progenitor cell line. Our data support the importance of a critical regulatory region (SRO) proximal to the hESC-specific TAD boundary. We further narrow this critical region by a deletion distal to the hESC-specific boundary, associated with a milder clinical phenotype. The distance from FOXG1 to the SRO ( > 500 kb) highlight a limitation of ENCODE DNase hypersensitivity data for functional prediction of LRPE. Moreover, the SRO has little overlap with a cluster of frequently associating regions (FIREs) located in the proximal hESC-TAD.

MeCP2 Deficiency in Neuroglia: New Progress in the Pathogenesis of Rett Syndrome

Rett syndrome (RTT) is an X-linked neurodevelopmental disease predominantly caused by mutations of the methyl-CpG-binding protein 2 (MeCP2) gene. Generally, RTT has been attributed to neuron-centric dysfunction. However, increasing evidence has shown that glial abnormalities are also involved in the pathogenesis of RTT. Mice that are MeCP2-null specifically in glial cells showed similar behavioral and/or neuronal abnormalities as those found in MeCP2-null mice, a mouse model of RTT. MeCP2 deficiency in astrocytes impacts the expression of glial intermediate filament proteins such as fibrillary acidic protein (GFAP) and S100 and induces neuron toxicity by disturbing glutamate metabolism or enhancing microtubule instability. MeCP2 deficiency in oligodendrocytes (OLs) results in down-regulation of myelin gene expression and impacts myelination. While MeCP2-deficient microglia cells fail in response to environmental stimuli, release excessive glutamate, and aggravate impairment of the neuronal circuit. In this review, we mainly focus on the progress in determining the role of MeCP2 in glial cells involved in RTT, which may provide further insight into a therapeutic intervention for RTT.

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

PurposeThe study aimed at widening the clinical and genetic spectrum and assessing genotype-phenotype associations in FOXG1 syndrome due to FOXG1 variants.MethodsWe compiled 30 new and 53 reported patients with a heterozygous pathogenic or likely pathogenic variant in FOXG1. We grouped patients according to type and location of the variant. Statistical analysis of molecular and clinical data was performed using Fisher's exact test and a nonparametric multivariate test.ResultsAmong the 30 new patients, we identified 19 novel FOXG1 variants. Among the total group of 83 patients, there were 54 variants: 20 frameshift (37%), 17 missense (31%), 15 nonsense (28%), and 2 in-frame variants (4%). Frameshift and nonsense variants are distributed over all FOXG1 protein domains; missense variants cluster within the conserved forkhead domain. We found a higher phenotypic variability than previously described. Genotype-phenotype association revealed significant differences in psychomotor development and neurological features between FOXG1 genotype groups. More severe phenotypes were associated with truncating FOXG1 variants in the N-terminal domain and the forkhead domain (except conserved site 1) and milder phenotypes with missense variants in the forkhead conserved site 1.ConclusionsThese data may serve for improved interpretation of new FOXG1 sequence variants and well-founded genetic counseling.

RettBASE: Rett syndrome database update

Rett syndrome (RTT) is an X-linked progressive neurodevelopmental disorder that primarily affects females. Mutations in the MECP2 gene have been attributed as the major genetic cause of RTT. Recently, mutations in CDKL5 and FOXG1 genes have also been suggested to give rise to RTT, although subsequent more extensive studies suggest that diseases resulting from mutations in these two genes should be considered as distinct clinical entities. While the genetic basis for the RTT has been recognized, so far there is no effective cure for the disease and the treatments available are mainly aimed at ameliorating clinical problems associated with the disorder. The swift identification of the mutations in children is crucial for pursuing the best therapeutic care. RettBASE was created in 2002 as a MECP2 variant database and has grown to become a comprehensive variant database for RTT and related clinical phenotypes, containing a curated collection of variants for MECP2, CDKL5, and FOXG1 genes. Here, we describe the development and growth of RettBASE after its inception in 2001. Currently, RettBASE holds a total of 4,668 variants in MECP2, 498 variants in CDKL5, and 64 variants in FOXG1.

Elevated FOXG1 and SOX2 in glioblastoma enforces neural stem cell identity through transcriptional control of cell cycle and epigenetic regulators

Glioblastoma multiforme (GBM) is an aggressive brain tumor driven by cells with hallmarks of neural stem (NS) cells. GBM stem cells frequently express high levels of the transcription factors FOXG1 and SOX2. Here we show that increased expression of these factors restricts astrocyte differentiation and can trigger dedifferentiation to a proliferative NS cell state. Transcriptional targets include cell cycle and epigenetic regulators (e.g., Foxo3, Plk1, Mycn, Dnmt1, Dnmt3b, and Tet3). Foxo3 is a critical repressed downstream effector that is controlled via a conserved FOXG1/SOX2-bound cis-regulatory element. Foxo3 loss, combined with exposure to the DNA methylation inhibitor 5-azacytidine, enforces astrocyte dedifferentiation. DNA methylation profiling in differentiating astrocytes identifies changes at multiple polycomb targets, including the promoter of Foxo3 In patient-derived GBM stem cells, CRISPR/Cas9 deletion of FOXG1 does not impact proliferation in vitro; however, upon transplantation in vivo, FOXG1-null cells display increased astrocyte differentiation and up-regulate FOXO3. In contrast, SOX2 ablation attenuates proliferation, and mutant cells cannot be expanded in vitro. Thus, FOXG1 and SOX2 operate in complementary but distinct roles to fuel unconstrained self-renewal in GBM stem cells via transcriptional control of core cell cycle and epigenetic regulators.

Modeling autism spectrum disorders with human neurons

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders characterized by impaired social communication and interactions and by restricted and repetitive behaviors. Although ASD is suspected to have a heritable or sporadic genetic basis, its underlying etiology and pathogenesis are not well understood. Therefore, viable human neurons and glial cells produced using induced pluripotent stem cells (iPSC) to reprogram cells from individuals affected with ASD provide an unprecedented opportunity to elucidate the pathophysiology of these disorders, providing novel insights regarding ASD and a potential platform to develop and test therapeutic compounds. Herein, we discuss the state of art with regards to ASD modeling, including limitations of this technology, as well as potential future directions. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Apoptotic Activity of MeCP2 Is Enhanced by C-Terminal Truncating Mutations

Methyl-CpG binding protein 2 (MeCP2) is a widely abundant, multifunctional protein most highly expressed in post-mitotic neurons. Mutations causing Rett syndrome and related neurodevelopmental disorders have been identified along the entire MECP2 locus, but symptoms vary depending on mutation type and location. C-terminal mutations are prevalent, but little is known about the function of the MeCP2 C-terminus. We employ the genetic efficiency of Drosophila to provide evidence that expression of p.Arg294* (more commonly identified as R294X), a human MECP2 E2 mutant allele causing truncation of the C-terminal domains, promotes apoptosis of identified neurons in vivo. We confirm this novel finding in HEK293T cells and then use Drosophila to map the region critical for neuronal apoptosis to a small sequence at the end of the C-terminal domain. In vitro studies in mammalian systems previously indicated a role of the MeCP2 E2 isoform in apoptosis, which is facilitated by phosphorylation at serine 80 (S80) and decreased by interactions with the forkhead protein FoxG1. We confirm the roles of S80 phosphorylation and forkhead domain transcription factors in affecting MeCP2-induced apoptosis in Drosophila in vivo, thus indicating mechanistic conservation between flies and mammalian cells. Our findings are consistent with a model in which C- and N-terminal interactions are required for healthy function of MeCP2.

Delineation of the movement disorders associated with FOXG1 mutations

Objective:

The primary objective of this research was to characterize the movement disorders associated with FOXG1 mutations.

Methods:

We identified patients with FOXG1 mutations who were referred to either a tertiary movement disorder clinic or tertiary epilepsy service and retrospectively reviewed medical records, clinical investigations, neuroimaging, and available video footage. We administered a telephone-based questionnaire regarding the functional impact of the movement disorders and perceived efficacy of treatment to the caregivers of one cohort of participants.

Results:

We identified 28 patients with FOXG1 mutations, of whom 6 had previously unreported mutations. A wide variety of movement disorders were identified, with dystonia, choreoathetosis, and orolingual/facial dyskinesias most commonly present. Ninety-three percent of patients had a mixed movement disorder phenotype. In contrast to the phenotype classically described with FOXG1 mutations, 4 patients with missense mutations had a milder phenotype, with independent ambulation, spoken language, and normocephaly. Hyperkinetic involuntary movements were a major clinical feature in these patients. Of the symptomatic treatments targeted to control abnormal involuntary movements, most did not emerge as clearly beneficial, although 4 patients had a caregiver-reported response to levodopa.

Conclusions:

Abnormal involuntary movements are a major feature of FOXG1 mutations. Our study delineates the spectrum of movement disorders and confirms an expanding clinical phenotype. Symptomatic treatment may be considered for severe or disabling cases, although further research regarding potential treatment strategies is necessary.

Testing for Ancient Selection Using Cross-population Allele Frequency Differentiation

A powerful way to detect selection in a population is by modeling local allele frequency changes in a particular region of the genome under scenarios of selection and neutrality and finding which model is most compatible with the data. A previous method based on a cross-population composite likelihood ratio (XP-CLR) uses an outgroup population to detect departures from neutrality that could be compatible with hard or soft sweeps, at linked sites near a beneficial allele. However, this method is most sensitive to recent selection and may miss selective events that happened a long time ago. To overcome this, we developed an extension of XP-CLR that jointly models the behavior of a selected allele in a three-population tree. Our method - called "3-population composite likelihood ratio" (3P-CLR) - outperforms XP-CLR when testing for selection that occurred before two populations split from each other and can distinguish between those events and events that occurred specifically in each of the populations after the split. We applied our new test to population genomic data from the 1000 Genomes Project, to search for selective sweeps that occurred before the split of Yoruba and Eurasians, but after their split from Neanderthals, and that could have led to the spread of modern-human-specific phenotypes. We also searched for sweep events that occurred in East Asians, Europeans, and the ancestors of both populations, after their split from Yoruba. In both cases, we are able to confirm a number of regions identified by previous methods and find several new candidates for selection in recent and ancient times. For some of these, we also find suggestive functional mutations that may have driven the selective events.

FOXG1-Dependent Dysregulation of GABA/Glutamate Neuron Differentiation in Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a disorder of brain development. Most cases lack a clear etiology or genetic basis, and the difficulty of re-enacting human brain development has precluded understanding of ASD pathophysiology. Here we use three-dimensional neural cultures (organoids) derived from induced pluripotent stem cells (iPSCs) to investigate neurodevelopmental alterations in individuals with severe idiopathic ASD. While no known underlying genomic mutation could be identified, transcriptome and gene network analyses revealed upregulation of genes involved in cell proliferation, neuronal differentiation, and synaptic assembly. ASD-derived organoids exhibit an accelerated cell cycle and overproduction of GABAergic inhibitory neurons. Using RNA interference, we show that overexpression of the transcription factor FOXG1 is responsible for the overproduction of GABAergic neurons. Altered expression of gene network modules and FOXG1 are positively correlated with symptom severity. Our data suggest that a shift toward GABAergic neuron fate caused by FOXG1 is a developmental precursor of ASD.

Imbalance of excitatory/inhibitory synaptic protein expression in iPSC-derived neurons from FOXG1(+/-) patients and in foxg1(+/-) mice

Rett syndrome (RTT) is a severe neurodevelopmental disorder associated with mutations in either MECP2, CDKL5 or FOXG1. The precise molecular mechanisms that lead to the pathogenesis of RTT have yet to be elucidated. We recently reported that expression of GluD1 (orphan glutamate receptor δ-1 subunit) is increased in iPSC-derived neurons obtained from patients with mutations in either MECP2 or CDKL5. GluD1 controls synaptic differentiation and shifts the balance between excitatory and inhibitory synapses toward the latter. Thus, an increase in GluD1 might be a critical factor in the etiology of RTT by affecting the excitatory/inhibitory balance in the developing brain. To test this hypothesis, we generated iPSC-derived neurons from FOXG1(+/-) patients. We analyzed mRNA and protein levels of GluD1 together with key markers of excitatory and inhibitory synapses in these iPSC-derived neurons and in Foxg1(+/-) mouse fetal (E11.5) and adult (P70) brains. We found strong correlation between iPSC-derived neurons and fetal mouse brains, where GluD1 and inhibitory synaptic markers (GAD67 and GABA AR-α1) were increased, whereas the levels of a number of excitatory synaptic markers (VGLUT1, GluA1, GluN1 and PSD-95) were decreased. In adult mice, GluD1 was decreased along with all GABAergic and glutamatergic markers. Our findings further the understanding of the etiology of RTT by introducing a new pathological event occurring in the brain of FOXG1(+/-) patients during embryonic development and its time-dependent shift toward a general decrease in brain synapses.

Familial recurrences of FOXG1-related disorder: Evidence for mosaicism

FOXG1-related disorders are caused by heterozygous mutations in FOXG1 and result in a spectrum of neurodevelopmental phenotypes including postnatal microcephaly, intellectual disability with absent speech, epilepsy, chorea, and corpus callosum abnormalities. The recurrence risk for de novo mutations in FOXG1-related disorders is assumed to be low. Here, we describe three unrelated sets of full siblings with mutations in FOXG1 (c.515_577del63, c.460dupG, and c.572T > G), representing familial recurrence of the disorder. In one family, we have documented maternal somatic mosaicism for the FOXG1 mutation, and all of the families presumably represent parental gonadal (or germline) mosaicism. To our knowledge, mosaicism has not been previously reported in FOXG1-related disorders. Therefore, this report provides evidence that germline mosaicism for FOXG1 mutations is a likely explanation for familial recurrence and should be considered during recurrence risk counseling for families of children with FOXG1-related disorders.

Switching modes in corticogenesis: mechanisms of neuronal subtype transitions and integration in the cerebral cortex

Information processing in the cerebral cortex requires the activation of diverse neurons across layers and columns, which are established through the coordinated production of distinct neuronal subtypes and their placement along the three-dimensional axis. Over recent years, our knowledge of the regulatory mechanisms of the specification and integration of neuronal subtypes in the cerebral cortex has progressed rapidly. In this review, we address how the unique cytoarchitecture of the neocortex is established from a limited number of progenitors featuring neuronal identity transitions during development. We further illuminate the molecular mechanisms of the subtype-specific integration of these neurons into the cerebral cortex along the radial and tangential axis, and we discuss these key features to exemplify how neocortical circuit formation accomplishes economical connectivity while maintaining plasticity and evolvability to adapt to environmental changes.

[Molecular basis of Rett syndrome: A current look]

Rett syndrome (RS) is a neurodevelopmental disorder that exclusively affects girls, and occurs along with autism. It is very uncommon, and has five distinct forms, one classic and the others atypical, which generally compromise manual skills, language, and mobility, and widely associated with the appearance of stereotypy and early epilepsy. With the aim of updating the information about RS, a search was performed in the computer data bases of PubMed, Hinari, SCIELO and Medline, as well as consulting other web sites including OMIM, ORPHANET, GeneMap, Genetests, Proteins and Gene, using the descriptors "Síndrome de Rett", "genes y Síndrome de Rett", "Rett Syndrome gene", "Rett Syndrome", "Rett Syndrome gene therapy", and "Rett Syndrome review". Of the 1,348 articles found, 42 articles were selected, which reported 3 genes causing the syndrome: MECP2, CDKL5 and FOXG. The MECP2 gene is mutated in 80% of patients with classic RS, as well as in 40% of those affected by any of its atypical forms. RS with early epilepsy and the congenital variant are mainly due to variations in the CDKL5 and FOXG1 genes, respectively.

CONCLUSIONS

The diagnosis of RS is based on clinical criteria. However, the advances in molecular biology and genetics have opened a wide range of possibilities for diagnosing the different clinical forms that could not be classified before. Molecular analysis can help confirm the clinical criteria and provided information as regards the prognosis of the patient.

FOXG1 Mutation is a Low-Incidence Genetic Cause in Atypical Rett Syndrome

Due to the genetic and clinical heterogeneity of Rett syndrome, patients with nonclassic phenotypes are classified as an atypical Rett syndrome, that is, preserved speech variant, early seizure variant, and congenital variant. Respectively, MECP2, CDKL5, and FOXG1 have been found to be the causative genes, but FOXG1 variants are the rarest and least studied. We performed mutational analyses for FOXG1 on 11 unrelated patients without MECP2 and CDKL5 mutations, who were diagnosed with atypical Rett syndrome. One patient, who suffered from severe early-onset mental retardation and multiple-type intractable seizures, carried a novel, de novo FOXG1 mutation (p.Gln70Pro). This case concurs with previous studies that have reported yields of ∼10%. FOXG1-related atypical Rett syndrome is rare in Korean population, but screening of this gene in patients with severe mental retardation, microcephaly, and early-onset multiple seizure types without specific genetic causes can help broaden the phenotypic spectrum of the distinct FOXG1-related syndrome.

Neurodevelopmental and neurobehavioral characteristics in males and females with CDKL5 duplications

Point mutations and genomic deletions of the CDKL5 (STK9) gene on chromosome Xp22 have been reported in patients with severe neurodevelopmental abnormalities, including Rett-like disorders. To date, only larger-sized (8-21 Mb) duplications harboring CDKL5 have been described. We report seven females and four males from seven unrelated families with CDKL5 duplications 540-935 kb in size. Three families of different ethnicities had identical 667kb duplications containing only the shorter CDKL5 isoform. Four affected boys, 8-14 years of age, and three affected girls, 6-8 years of age, manifested autistic behavior, developmental delay, language impairment, and hyperactivity. Of note, two boys and one girl had macrocephaly. Two carrier mothers of the affected boys reported a history of problems with learning and mathematics while at school. None of the patients had epilepsy. Similarly to CDKL5 mutations and deletions, the X-inactivation pattern in all six studied females was random. We hypothesize that the increased dosage of CDKL5 might have affected interactions of this kinase with its substrates, leading to perturbation of synaptic plasticity and learning, and resulting in autistic behavior, developmental and speech delay, hyperactivity, and macrocephaly.

Epilepsy and outcome in FOXG1-related disorders

OBJECTIVE

FOXG1-related disorders are associated with severe intellectual disability, absent speech with autistic features, and epilepsy. Children with deletions or intragenic mutations of FOXG1 also have postnatal microcephaly, morphologic abnormalities of the corpus callosum, and choreiform movements. Duplications of 14q12 often present with infantile spasms, and have subsequent intellectual disability with autistic features. Long-term epilepsy outcome and response to treatment have not been studied systematically in a well-described cohort of subjects with FOXG1-related disorders. We report on the epilepsy features and developmental outcome of 23 new subjects with deletions or intragenic mutations of FOXG1, and 7 subjects with duplications.

METHODS

Subjects had either chromosomal microarray or FOXG1 gene sequencing performed as part of routine clinical care. Development and epilepsy follow-up data were collected from medical records from treating neurologists and through telephone parental interviews using standardized questionnaires.

RESULTS

Epilepsy was diagnosed in 87% of the subjects with FOXG1-related disorders. The mean age of epilepsy diagnosis in FOXG1 duplications was significantly younger than those with deletions/intragenic mutations (p = 0.0002). All of the duplication FOXG1 children with infantile spasms responded to hormonal therapy, and only one required long-term antiepileptic therapy. In contrast, more children with deletions/intragenic mutations required antiepileptic drugs on follow-up (p < 0.0005). All subjects with FOXG1-related disorders had neurodevelopmental disabilities after 3 years of age, regardless of the epilepsy type or intractability of seizures. All had impaired verbal language and social contact, and three duplication subjects were formally diagnosed with autism. Subjects with deletion/intragenic mutations, however, had significantly worse ambulation (p = 0.04) and functional hand use (p < 0.0005).

SIGNIFICANCE

Epilepsy and developmental outcome characteristics allow clinicians to distinguish among the FOXG1-related disorders. Further genotype-phenotype studies of FOXG1 may help to elucidate why children develop different forms of developmental epilepsy.

Over-expression of either MECP2_e1 or MECP2_e2 in neuronally differentiated cells results in different patterns of gene expression

Mutations in MECP2 are responsible for the majority of Rett syndrome cases. MECP2 is a regulator of transcription, and has two isoforms, MECP2_e1 and MECP2_e2. There is accumulating evidence that MECP2_e1 is the etiologically relevant variant for Rett. In this study we aim to detect genes that are differentially transcribed in neuronal cells over-expressing either of these two MECP2 isoforms. The human neuroblastoma cell line SK-N-SH was stably infected by lentiviral vectors over-expressing MECP2_e1, MECP2_e2, or eGFP, and were then differentiated into neurons. The same lentiviral constructs were also used to infect mouse Mecp2 knockout (Mecp2^tm1.1Bird) fibroblasts. RNA from these cells was used for microarray gene expression analysis. For the human neuronal cells, ∼800 genes showed >three-fold change in expression level with the MECP2_e1 construct, and ∼230 with MECP2_e2 (unpaired t-test, uncorrected p value <0.05). We used quantitative RT-PCR to verify microarray results for 41 of these genes. We found significant up-regulation of several genes resulting from over-expression of MECP2_e1 including SRPX2, NAV3, NPY1R, SYN3, and SEMA3D. DOCK8 was shown via microarray and qRT-PCR to be upregulated in both SK-N-SH cells and mouse fibroblasts. Both isoforms up-regulated GABRA2, KCNA1, FOXG1 and FOXP2. Down-regulation of expression in the presence of MECP2_e1 was seen with UNC5C and RPH3A. Understanding the biology of these differentially transcribed genes and their role in neurodevelopment may help us to understand the relative functions of the two MECP2 isoforms, and ultimately develop a better understanding of RTT etiology and determine the clinical relevance of isoform-specific mutations.

Dysregulation of the IGF-I/PI3K/AKT/mTOR signaling pathway in autism spectrum disorders

The IGF-I/PI3K/AKT/mTOR signaling pathway plays an important role in the regulation of cell growth, proliferation, differentiation, motility, survival, metabolism and protein synthesis. Insulin-like growth factor-I (IGF-I) is synthesized in the liver and fibroblasts, and its biological actions are mediated by the IGF-I receptor (IGF-IR). The binding of IGF-I to IGF-IR leads to the activation of phosphatidylinositol 3-kinase (PI3K). Activated PI3K stimulates the production of phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2] and phosphatidylinositol (3,4,5)-trisphosphate [PI(3,4,5)P3]. The PH domain of AKT (protein kinase B, PKB) (v-AKT murine thymoma viral oncogene homolog) binds to PI(4,5)P2 and PI(3,4,5)P3, followed by phosphorylation of the Thr308 and Ser473 regulatory sites. Tuberous sclerosis complex 1 (TSC1) and TSC2 are upstream regulators of mammalian target of rapamycin (mTOR) and downstream effectors of the PI3K/AKT signaling pathway. The activation of AKT suppresses the TSC1/TSC2 heterodimer, which is an upstream regulator of mTOR. Dysregulated IGF-I/PI3K/AKT/mTOR signaling has been shown to be associated with autism spectrum disorders (ASDs). In this review, we discuss the emerging evidence for a functional relationship between the IGF-I/PI3K/AKT/mTOR pathway and ASDs, as well as a possible role of this signaling pathway in the diagnosis and treatment of ASDs.

Novel mutation in forkhead box G1 (FOXG1) gene in an Indian patient with Rett syndrome

Rett syndrome (RTT) is a severe neurodevelopmental disorder characterized by the progressive loss of intellectual functioning, fine and gross motor skills and communicative abilities, deceleration of head growth, and the development of stereotypic hand movements, occurring after a period of normal development. The classic form of RTT involves mutation in MECP2 while the involvement of CDKL5 and FOXG1 genes has been identified in atypical RTT phenotype. FOXG1 gene encodes for a fork-head box protein G1, a transcription factor acting primarily as transcriptional repressor through DNA binding in the embryonic telencephalon as well as a number of other neurodevelopmental processes. In this report we have described the molecular analysis of FOXG1 gene in Indian patients with Rett syndrome. FOXG1 gene mutation analysis was done in a cohort of 34 MECP2/CDKL5 mutation negative RTT patients. We have identified a novel mutation (p. D263VfsX190) in FOXG1 gene in a patient with congenital variant of Rett syndrome. This mutation resulted into a frameshift, thereby causing an alteration in the reading frames of the entire coding sequence downstream of the mutation. The start position of the frameshift (Asp263) and amino acid towards the carboxyl terminal end of the protein was found to be well conserved across species using multiple sequence alignment. Since the mutation is located at forkhead binding domain, the resultant mutation disrupts the secondary structure of the protein making it non-functional. This is the first report from India showing mutation in FOXG1 gene in Rett syndrome.