Pathophysiological Heterogeneity of the BBSOA Neurodevelopmental Syndrome

Unravelling the conundrum of nucleolar NR2F1 localization using antibody-based approaches in vitro and in vivo

As a transcription factor, NR2F1 regulates spatiotemporal gene expression in the nucleus particularly during development. Aberrant NR2F1 causes the rare neurodevelopmental disorder Bosch-Boonstra-Schaaf Optic Atrophy Syndrome. In addition, altered NR2F1 expression is frequently observed in various cancers and is considered a prognostic marker or potential therapeutic target. NR2F1 has been found in both the nucleus and nucleoli, suggesting a non-canonical and direct role in the latter compartment. Hence, we studied this phenomenon employing various in vitro and in vivo models using different antibody-dependent approaches. Examination of seven commonly used anti-NR2F1 antibodies in different human cancer and stem cells as well as in wild type and null mice revealed that NR2F1 nucleolar localization is artificial and has no functional role. Our subsequent comparative analysis demonstrated which anti-NR2F1 antibody best fits which approach. The data allow for correct data interpretation and underline the need to optimize any antibody-mediated technique.

A pathogenic NR2F1 gene variant disrupts transcriptional activity and causes severe neurodevelopmental delay in Bosch-Boonstra-Schaaf syndrome

INTRODUCTION

Nuclear receptor subfamily 2, group F, member 1 (NR2F1) gene variations are associated with Bosch-Boonstra-Schaaf optic atrophy syndrome. The NR2F1 genotype correlates with its phenotype; variants within the DNA-binding domain may cause severe psychomotor developmental disorders. However, the mechanisms underlying these phenotypes remain unclear.

METHODS

Whole-exome sequencing was performed on the proband and her parents DNA. Candidate variants were verified by Sanger sequencing and bioinformatics analyses. Molecular dynamics simulations were performed to predict structural changes in the mutant NR2F1 protein. A dual-luciferase assay was used to analyze the variant's effect on transcriptional activation.

RESULTS

The proband was a 10-month-old girl with severe motor and cognitive developmental delays accompanied by bilateral optic nerve pallor. Genetic testing revealed a novel NR2F1 gene variant, NM_005654.6: c.452T > A (p.Met151Lys). Bioinformatics analysis suggested that this variant alters the protein structure or function. The molecular dynamics analysis showed that this variant might affect the stability of the zinc finger structure within the NR2F1 DNA-binding domain. Dual-luciferase assays indicated this variant affects transcriptional activation.

CONCLUSIONS

The NR2F1 variant c.452T > A (p.Met151Lys) may genetically cause the severe clinical phenotypes observed in this patient. This finding expands the spectrum of NR2F1 variants.

The Natural Course of Bosch-Boonstra-Schaaf Optic Atrophy Syndrome

(Likely) pathogenic variants in NR2F1 are associated with Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS, OMIM #615722), a rare neurodevelopmental disorder. Patients present with a variety of symptoms, including intellectual disability, developmental delay, visual impairment, muscular hypotonia, seizures, and/or autistic features. Since it was first described in 2014, the phenotype has steadily expanded. However, there is limited information regarding the natural course of the disorder. Here, we present data on genetic variants and phenotype development of 47 individuals who responded to our questionnaire. A questionnaire was developed to assess the phenotype more comprehensively and to better understand the course of symptoms. In addition, families sent medical documents and photographs. To investigate the genotype-phenotype correlation in our cohort, we compared clinical features of two genotypically distinct groups (variants in the DNA-binding domain (DBD, n = 17) versus variants elsewhere in the gene (n = 30)). We observed a range of common symptoms including developmental delay, muscular hypotonia, optic atrophy, nystagmus, strabismus, autistic features, and thin corpus callosum on brain MRI. Overall, more improvement than worsening was reported. Individuals with variants in the DBD showed a higher prevalence of severe clinical features, such as infantile spasms (46.7% vs. 3.8%, p = 0.002) or nonverbality (50% vs. 3.4%, p = 0.0004), age at diagnosis was statistically significantly different between the two genotypic groups (mean 4.7 years vs. 8.9 years, p = 0.048). Our study confirms characteristic clinical features of BBSOAS. Variants in the DBD are associated with a more severe clinical phenotype. We found no evidence that the disease progresses; rather, several symptoms are reported to improve over time. However, prospective longitudinal studies are needed to further investigate disease progression.

Second Case of Gonadal Mosaicism and a Novel Nonsense NR2F1 Gene Variant as the Cause of Bosch-Boonstra-Schaaf Optic Atrophy Syndrome

Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS) is an autosomal dominant disease characterized by developmental delay, intellectual disability, and optic atrophy with a variable expression of other clinical features (dysmorphic features, autistic behaviour, corpus callosum hypoplasia and seizures). To date, approximately a hundred cases of the syndrome have been described, with an estimated prevalence of 1 in 100 000-250 000. BBSOAS is caused by the loss of function of the NR2F1 gene (nuclear receptor subfamily 2 group F member 1), which encodes the COUP-TFI (Chicken ovalbumin upstream promotor-transcription factor 1). COUP-TFI functions as a homodimer and is one of the major transcriptional regulators directing cortical arealization, cell differentiation and maturation. Most cases of BBSOAS occur de novo, and one case was previously described in which the disease resulted from gonadal mosaicism. In the present case, we report two sisters with BBSOAS, a novel nonsense mutation in the NR2F1 gene and potential gonadal mosaicism as the cause of this rare disease, making it the second such case described in the literature.

FGF8-mediated gene regulation affects regional identity in human cerebral organoids

The morphogen FGF8 establishes graded positional cues imparting regional cellular responses via modulation of early target genes. The roles of FGF signaling and its effector genes remain poorly characterized in human experimental models mimicking early fetal telencephalic development. We used hiPSC-derived cerebral organoids as an in vitro platform to investigate the effect of FGF8 signaling on neural identity and differentiation. We found that FGF8 treatment increases cellular heterogeneity, leading to distinct telencephalic and mesencephalic-like domains that co-develop in multi-regional organoids. Within telencephalic regions, FGF8 affects the anteroposterior and dorsoventral identity of neural progenitors and the balance between GABAergic and glutamatergic neurons, thus impacting spontaneous neuronal network activity. Moreover, FGF8 efficiently modulates key regulators responsible for several human neurodevelopmental disorders. Overall, our results show that FGF8 signaling is directly involved in both regional patterning and cellular diversity in human cerebral organoids and in modulating genes associated with normal and pathological neural development.

Mitochondrial regulation of adult hippocampal neurogenesis: Insights into neurological function and neurodevelopmental disorders

Mitochondria are essential regulators of cellular energy metabolism and play a crucial role in the maintenance and function of neuronal cells. Studies in the last decade have highlighted the importance of mitochondrial dynamics and bioenergetics in adult neurogenesis, a process that significantly influences cognitive function and brain plasticity. In this review, we examine the mechanisms by which mitochondria regulate adult neurogenesis, focusing on the impact of mitochondrial function on the behavior of neural stem/progenitor cells and the maturation and plasticity of newborn neurons in the adult mouse hippocampus. In addition, we explore the link between mitochondrial dysfunction, adult hippocampal neurogenesis and genes associated with cognitive deficits in neurodevelopmental disorders. In particular, we provide insights into how alterations in the transcriptional regulator NR2F1 affect mitochondrial dynamics and may contribute to the pathophysiology of the emerging neurodevelopmental disorder Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS). Understanding how genes involved in embryonic and adult neurogenesis affect mitochondrial function in neurological diseases might open new directions for therapeutic interventions aimed at boosting mitochondrial function during postnatal life.

Biallelic loss-of-function variants of ZFTRAF1 cause neurodevelopmental disorder with microcephaly and hypotonia

PURPOSE

Neurodevelopmental disorders exhibit clinical and genetic heterogeneity, ergo manifest dysfunction in components of diverse cellular pathways; the precise pathomechanism for the majority remains elusive.

METHODS

We studied 5 affected individuals from 3 unrelated families manifesting global developmental delay, postnatal microcephaly, and hypotonia. We used exome sequencing and prioritized variants that were subsequently characterized using immunofluorescence, immunoblotting, pulldown assays, and RNA sequencing.

RESULTS

We identified biallelic variants in ZFTRAF1, encoding a protein of yet unknown function. Four affected individuals from 2 unrelated families segregated 2 homozygous frameshift variants in ZFTRAF1, whereas, in the third family, an intronic splice site variant was detected. We investigated ZFTRAF1 at the cellular level and signified it as a nucleocytoplasmic protein in different human cell lines. ZFTRAF1 was completely absent in the fibroblasts of 2 affected individuals. We also identified 110 interacting proteins enriched in mRNA processing and autophagy-related pathways. Based on profiling of autophagy markers, patient-derived fibroblasts show irregularities in the protein degradation process.

CONCLUSION

Thus, our findings suggest that biallelic variants of ZFTRAF1 cause a severe neurodevelopmental disorder.

Disrupted protein interaction dynamics in a genetic neurodevelopmental disorder revealed by structural bioinformatics and genetic code expansion

Deciphering the structural effects of gene variants is essential for understanding the pathophysiological mechanisms of genetic diseases. Using a neurodevelopmental disorder called Bosch-Boonstra-Schaaf Optic Atrophy Syndrome (BBSOAS) as a genetic disease model, we applied structural bioinformatics and Genetic Code Expansion (GCE) strategies to assess the pathogenic impact of human NR2F1 variants and their binding with known and novel partners. While the computational analyses of the NR2F1 structure delineated the molecular basis of the impact of several variants on the isolated and complexed structures, the GCE enabled covalent and site-specific capture of transient supramolecular interactions in living cells. This revealed the variable quaternary conformations of NR2F1 variants and highlighted the disrupted interplay with dimeric partners and the newly identified co-factor, CRABP2. The disclosed consequence of the pathogenic mutations on the conformation, supramolecular interplay, and alterations in the cell cycle, viability, and sub-cellular localization of the different variants reflect the heterogeneous disease spectrum of BBSOAS and set up novel foundation for unveiling the complexity of neurodevelopmental diseases.

Structural interhemispheric connectivity defects in mouse models of BBSOAS: Insights from high spatial resolution 3D white matter tractography

White matter (WM) tract formation and axonal pathfinding are major processes in brain development allowing to establish precise connections between targeted structures. Disruptions in axon pathfinding and connectivity impairments will lead to neural circuitry abnormalities, often associated with various neurodevelopmental disorders (NDDs). Among several neuroimaging methodologies, Diffusion Tensor Imaging (DTI) is a magnetic resonance imaging (MRI) technique that has the advantage of visualizing in 3D the WM tractography of the whole brain non-invasively. DTI is particularly valuable in unpinning structural tract connectivity defects of neural networks in NDDs. In this study, we used 3D DTI to unveil brain-specific tract defects in two mouse models lacking the Nr2f1 gene, which mutations in patients have been proven to cause an emerging NDD, called Bosch-Boonstra-Schaaf Optic Atrophy (BBSOAS). We aimed to investigate the impact of the lack of cortical Nr2f1 function on WM morphometry and tract microstructure quantifications. We found in both mutant mice partial loss of fibers and severe misrouting of the two major cortical commissural tracts, the corpus callosum, and the anterior commissure, as well as the two major hippocampal efferent tracts, the post-commissural fornix, and the ventral hippocampal commissure. DTI tract malformations were supported by 2D histology, 3D fluorescent imaging, and behavioral analyses. We propose that these interhemispheric connectivity impairments are consistent in explaining some cognitive defects described in BBSOAS patients, particularly altered information processing between the two brain hemispheres. Finally, our results highlight 3DDTI as a relevant neuroimaging modality that can provide appropriate morphometric biomarkers for further diagnosis of BBSOAS patients.

Infantile epileptic spasm syndrome as a new NR2F1 gene phenotype

INTRODUCTION

NR2F1 pathogenetic variants are associated with the Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS). Recent studies indicate that BBSOAS patients not only have visual impairments but may also have developmental delays, hypotonia, thin corpus callosum and epileptic seizures. However, reports of BBSOAS occurrence along with infantile epileptic spasm syndrome (IESS) are rare.

METHODS

Here, we report three cases involving children with IESS and BBSOAS caused by de novo NR2F1 pathogenetic variants and summarize the genotype, clinical characteristics, diagnosis and treatment of them.

RESULTS

All three children experienced epileptic spasms and global developmental delays, with brain Magnetic Resonance Imaging (MRI) suggesting abnormalities (thinning of the corpus callosum or widened extracerebral spaces) and two of the children exhibiting abnormal visual evoked potentials.

CONCLUSIONS

Our findings indicate that new missense NR2F1 pathogenetic variants may lead to IESS with abnormal visual evoked potentials. Thus, clinicians should be aware of the Bosch-Boonstra-Schaaf optic atrophy syndrome and regular monitoring of the fundus, and the optic nerve is necessary during follow-up.

Effective treatment of NR2F1-related epilepsy with perampanel

BACKGROUND

NR2F1 mutations are associated with Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS). Although ~ 46.7% of BBSOAS patients present with epilepsy, which is always drug-resistant and associated with higher rates of behavioral and cognitive problems, the treatment and outcomes of NR2F1-related epilepsy have rarely been described. Here, we present new cases of BBSOAS-related epilepsy and summarize all previously reported cases to explore the effective treatment for this type of epilepsy.

METHODS

We identified six new Chinese cases of BBSOAS with epilepsy. Five different de novo heterozygous NR2F1 mutations were identified in these cases, including two novel mutations c.365G > T, p.Cys122Phe and c.449G > T, p.Gly150Val. By combining the six cases and 14 previously reported cases, we analyzed the characteristics and treatment outcomes of NR2F1-related epilepsy.

RESULTS

Twelve of the 20 patients (60%) had infantile epileptic spasms, while the other patients had generalized tonic/tonic-clonic, focal, myoclonic, absence, or unclassified seizures. Several anti-seizure medications, steroids, and a ketogenic diet were administered in these cases. However, seizures were controlled in only 50% of previously reported cases, while all of the six new cases became seizure-free after perampanel as an add-on treatment. The average time from the addition of perampanel to seizure control was 7.33 ± 4.59 months (range, 1-12 months). The median time to seizure freedom was 14 months (1-32 months, > 19 months in 3 cases). The average dosage of perampanel needed for epilepsy control was 0.22 ± 0.17 mg/kg per day.

CONCLUSIONS

In this paper, we comprehensively summarized the clinical characteristics, treatments and outcomes of NR2F1-related epilepsy for the first time. Perampanel exhibits dramatic efficacy for NR2F1-related epilepsy. This will help optimize the treatment of this type of epilepsy and provide clues for its pathogenic mechanisms. The two novel mutations expand the genotype spectrum of this disease.

Design and Outcomes of a Novel Multidisciplinary Ophthalmic Genetics Clinic

The Multidisciplinary Ophthalmic Genetics Clinic (MOGC) at the University of Michigan Kellogg Eye Center aims to provide medical and ophthalmic genetics care to patients with inherited ocular conditions. We have developed a clinical and referral workflow where each patient undergoes coordinated evaluation by our multidisciplinary team followed by discussions on diagnosis, prognosis, and genetic testing. Testing approaches are specific to each patient and can be targeted (single-gene, gene panel), broad (chromosomal microarray, whole-exome sequencing), or a combination. We hypothesize that this clinic model improves patient outcomes and quality of care. A retrospective chart review of patients in the MOGC from July 2020 to October 2022 revealed that the most common referral diagnoses were congenital cataracts, optic neuropathy, and microphthalmia, with 52% syndromic cases. Within this patient cohort, we saw a 76% uptake for genetic testing, among which 33% received a diagnostic test result. Our results support a tailored approach to genetic testing for specific conditions. Through case examples, we highlight the power and impact of our clinic. By integrating ophthalmic care with medical genetics and counseling, the MOGC has not only helped solve individual patient diagnostic challenges but has aided the greater population in novel genetic discoveries and research towards targeted therapeutics.

Pathophysiological Mechanism of Neurodevelopmental Disorders-Overview

Technological advancements in next-generation DNA sequencing have enabled elucidation of many genetic causes of neurodevelopmental disorders (NDDs) over the last two decades [...].