FLNA regulates neuronal maturation by modulating RAC1-Cofilin activity in the developing cortex.

Periventricular nodular heterotopia (PNH), the most common brain malformation diagnosed in adulthood, is characterized by the presence of neuronal nodules along the ventricular walls. PNH is mainly associated with mutations in the FLNA gene - encoding an actin-binding protein - and patients often develop epilepsy. However, the molecular mechanisms underlying the neuronal failure still remain elusive. It has been hypothesized that dysfunctional cortical circuitry, rather than ectopic neurons, may explain the clinical manifestations. To address this issue, we depleted FLNA from cortical pyramidal neurons of a conditional Flnaflox/flox mice by timed in utero electroporation of Cre recombinase. We found that FLNA regulates dendritogenesis and spinogenesis thus promoting an appropriate excitatory/inhibitory inputs balance. We demonstrated that FLNA modulates RAC1 and cofilin activity through its interaction with the Rho-GTPase Activating Protein 24 (ARHGAP24). Collectively, we disclose an uncharacterized role of FLNA and provide strong support for neural circuit dysfunction being a consequence of FLNA mutations.

Genetic analysis of periventricular nodular heterotopia 7 caused by a novel NEDD4L missense mutation: Case and literature summary.

BACKGROUND: Neurodevelopmental disorders associated with periventricular nodular heterotopia (PVNH) are characterized by phenotypic and genetic heterogeneity. NEDD4L mutation can lead to PVNH7. However, at present, only eight NEDD4L pathogenic variants have been identified across 15 cases of PVNH7 worldwide. Given this dearth of evidence, the precise correlations between genetic pathogenesis and phenotypes remain to be determined. METHODS: This report discusses the case of a 19-month-old male child with cleft palate, seizures, psychomotor retardation, and hypotonia, for whom we verified the genetic etiology using Trio-whole-exome and Sanger sequencing to analyze the potential pathogenicity of the mutant protein structure. Mutant plasmids were constructed for in vitro analyses. After transfection into human 293 T cells, the mutant transcription process was analyzed using real-time PCR (RT-PCR), and levels of mutant protein expression were examined using western blotting (WB) and immunofluorescence (IF) experiments. RESULTS: Genetic analyses revealed a novel missense mutation Gln900Arg, located in the homologous to E6-APC terminal (HECT) domain of NEDD4L and that the parents were wild-type, suggestive of a de novo mutation. The variant was predicted to be pathogenic by bioinformatics software, which also suggested alterations in the structural stability of the mutant protein. RT-PCR results indicated that the mutation did not affect mRNA expression, whereas WB and IF results indicated that the level of mutant protein was significantly reduced by 41.07%. CONCLUSION: Functional experiments demonstrated that Gln900Arg probably did not lead to transcriptional abnormalities in this patient, instead leading to increased ubiquitination activity owing to the constitutive activation of the HECT domain, thereby promoting protein degradation. Extensive clinical reports should be generated for patients presenting with PVNH and/or polymicrogyria, developmental delay, syndactyly, and hypotonia to increase the pool of evidence related to NEDD4L.

Asymmetrical aortic root aneurism in patient with Filamin A mutation.

We report the case of a 28 years old woman with periventricular nodular heterotopia, due to Filamin A mutation. She had an asymmetrical aneurysm of the aortic root, involving, above all, noncoronary Valsalva sinus. She was asymptomatic and she had moderate aortic regurgitation. Reimplantation of the aortic valve with replacement of the aortic root was successfully accomplished. Filamin A is a protein that is encoded by the FLNA gene, which shows X-linked dominant inheritance. This protein is involved in neuronal migration, angiogenesis, cytoskeleton regulation, and cell signaling. Therefore, mutations of FLNA gene might result in brain, blood vessels, heart, and connective tissue disorders. A miscellany of cardiovascular abnormalities could be present in this subset of patients; cardiac symptoms may precede neurological manifestations. Aorta seems to be frequently affected. Consequently, in presence of FLNA gene mutations, cardiovascular evaluation should include vascular magnetic resonance imaging or computed tomography scan.

Ophthalmic Findings Associated with NEDD4L-related Disorder.

Pathogenic variants in the NEDD4L gene are associated with a very rare neurodevelopmental disorder characterized by periventricular nodular heterotopia, developmental delay, 2-3 toe syndactyly, and cleft palate. Ophthalmic findings associated with this disorder have not been well described in literature. We have summarized the clinical findings that have been reported in this disorder previously and highlight a novel ophthalmic finding of foveal hypoplasia in a new case of NEDD4L-related disorder.

Cerebral organoids to unravel the mechanisms underlying malformations of human cortical development.

Genetic studies identified multiple mutations associated with malformations of cortical development (MCD) in humans. When analyzing the underlying mechanisms in non-human experimental models it became increasingly evident, that these mutations accumulate in genes, which functions evolutionary progressed from rodents to humans resulting in an incomplete reflection of the molecular and cellular alterations in these models. Human brain organoids derived from human pluripotent stem cells resemble early aspects of human brain development to a remarkable extent making them an attractive model to investigate MCD. Here we review how human brain organoids enable the generation of fundamental new insight about the underlying pathomechanisms of MCD. We show how phenotypic features of these diseases are reflected in human brain organoids and discuss challenges and future considerations but also limitations for the use of human brain organoids to model human brain development and associated disorders.

Periventricular nodular heterotopia in a Chihuahua.

Periventricular nodular heterotopia is a common neuronal malformation in humans, often leading to epilepsy and other neurologic diseases. A 2-month-old female Chihuahua weighing 750 g was examined because of a history of epileptic seizures and abnormalities in gait and behavior. Results of the clinical examination were consistent with a multifocal neurologic disease with localization in the forebrain and spinovestibular system. The magnetic resonance imaging showed multiple bilateral periventricular nodules isointense to gray matter and ventriculomegaly. Histopathological and immunohistological examination of the brain revealed that periventricular nodules consisted of neurons, fewer astrocytes, and some oligodendroglia consistent with periventricular nodular heterotopias.

Internodular functional connectivity in heterotopia-related epilepsy.

OBJECTIVE: A vast network involving the nodules and overlying cortices is believed to be responsible for the epileptogenicity in gray matter heterotopia with multiple nodules, which often associated with difficult-to-treat epilepsy. We sought to determine if functional magnetic resonance imaging (fMRI) could detect internodular functional connectivity (FC), and if this connectivity reflects an actual synchronized neuronal activity and partakes in epileptogenicity. METHODS: We studied 16 epilepsy patients with multiple heterotopic nodules; eight underwent subsequent intracerebral EEG. We examined the internodular FC using fMRI and its correspondence with internodular synchrony of intracerebral interictal activity. We then compared the spreading speed of ictal activity between connected and unconnected nodules; and the FC among possible combinations of nodule pairs in terms of their involvement at seizure onset. RESULTS: Seventy nodules were studied: 83% have significant connection to at least one other nodule. Among the 49 pairs studied with intracerebral EEG, (1) synchronized interictal activity is more prevalent in fMRI-connected pairs (P < 0.05), (2) ictal activity spreads faster between connected pairs (P < 0.0001), and (3) stronger FC was observed between pairs in which both nodules were involved at seizure onset (P < 0.01). INTERPRETATION: fMRI could reliably and noninvasively detect the FC between heterotopic nodules. These functional connections correspond to the synchrony of interictal epileptic activity between the nodules and to the ability of nodules to generate synchronous seizure onsets or rapid seizure spread. These findings may help in understanding the complexity of the epileptogenic network in multiple heterotopic nodules and better targeting the likely epileptogenic nodules.

Altered neuronal migratory trajectories in human cerebral organoids derived from individuals with neuronal heterotopia.

Malformations of the human cortex represent a major cause of disability1. Mouse models with mutations in known causal genes only partially recapitulate the phenotypes and are therefore not unlimitedly suited for understanding the molecular and cellular mechanisms responsible for these conditions2. Here we study periventricular heterotopia (PH) by analyzing cerebral organoids derived from induced pluripotent stem cells (iPSCs) of patients with mutations in the cadherin receptor-ligand pair DCHS1 and FAT4 or from isogenic knockout (KO) lines1,3. Our results show that human cerebral organoids reproduce the cortical heterotopia associated with PH. Mutations in DCHS1 and FAT4 or knockdown of their expression causes changes in the morphology of neural progenitor cells and result in defective neuronal migration dynamics only in a subset of neurons. Single-cell RNA-sequencing (scRNA-seq) data reveal a subpopulation of mutant neurons with dysregulated genes involved in axon guidance, neuronal migration and patterning. We suggest that defective neural progenitor cell (NPC) morphology and an altered navigation system in a subset of neurons underlie this form of PH.

The clinical and imaging features of gray matter heterotopia: a clinical analysis on 15 patients.

OBJECTIVE: To investigate the clinical and imaging features of gray matter heterotopia (GMH) and improve the clinicians' understanding of the disease. METHODS: A retrospective study was performed on 15 patients with GMH diagnosed at The Affiliated Hospital of Xuzhou Medical University from November 2014 to November 2016. Their clinical and imaging features are also summarized. RESULTS: The proportion of male and female patients was 2:1. The age of onset was 2~45 years and the average age was 19.1 years. There were 13 patients with epilepsy who also had cognitive decline (5 cases) and neurological deficit (3 cases). There were 2 patients with headache or dizziness. The imaging findings of GMH are unilateral or multiple spots in the periventricular or subependymal, subcortical, and centrum semiovale and are often accompanied by other cerebral malformations. We found that 10 patients had the subcortical type of GMH and 5 patients had the subependymal type or periventricular nodular heterotopia type. There were 8 cases of ventricular compression, 5 cases of ventriculomegaly, 5 cases of cerebral fissure malformation, 3 cases of pachygyria, 1 case of callosal agenesis, and 1 case of undeveloped septum pellucidum. All the patients were given symptomatic and supportive therapies and 3 patients were treated with antiepileptic drugs. Seizures were, however, poorly controlled. CONCLUSION: GMH should also be suspected in patients with juvenile onset of seizures, cognitive decline, and neurological deficits. Magnetic resonance scans may show lesions in the white matter of the brain with signals similar to the normal gray matter.

Familial NEDD4L variant in periventricular nodular heterotopia and in a fetus with hypokinesia and flexion contractures.

BACKGROUND: Mutations in the HECT domain of NEDD4L have recently been identified in a cohort of eight patients with a syndromic form of bilateral periventricular nodular heterotopia (PVNH) in association with neurodevelopmental delay, cleft palate, and toe syndactyly (PVNH7). METHODS: Case report based on NGS sequencing. RESULTS: Here, we describe a girl with a novel heterozygous NEDD4L missense variant, p.Tyr679His, and characteristic clinical findings, including bilateral periventricular nodular heterotopia, cleft palate and mild toe syndactyly. Molecular testing from peripheral blood identified the healthy father to carry the NEDD4L variant in mosaic state. Notably, a previous pregnancy of the couple had been terminated due to a complex fetal developmental disorder, including hypokinesia and flexion contractures. Upon review, this affected fetus was also shown to carry the familial NEDD4L variant. CONCLUSION: Our findings may suggest a broader spectrum of NEDD4L-associated phenotypes, including severe prenatal neurodevelopmental manifestations, which might represent yet another genetic form of fetal hypokinesia with flexion contractures.

IRE1α governs cytoskeleton remodelling and cell migration through a direct interaction with filamin A.

Maintenance of endoplasmic reticulum (ER) proteostasis is controlled by a signalling network known as the unfolded protein response (UPR). Here, we identified filamin A as a major binding partner of the ER stress transducer IRE1α. Filamin A is an actin crosslinking factor involved in cytoskeleton remodelling. We show that IRE1α controls actin cytoskeleton dynamics and affects cell migration upstream of filamin A. The regulation of cytoskeleton dynamics by IRE1α is independent of its canonical role as a UPR mediator, serving instead as a scaffold that recruits and regulates filamin A. Targeting IRE1α expression in mice affected normal brain development, generating a phenotype resembling periventricular heterotopia, a disease linked to the loss of function of filamin A. IRE1α also modulated cell movement and cytoskeleton dynamics in fly and zebrafish models. This study unveils an unanticipated biological function of IRE1α in cell migration, whereby filamin A operates as an interphase between the UPR and the actin cytoskeleton.

The spectrum of structural and functional network alterations in malformations of cortical development.

Neuroimaging studies of malformations of cortical development have mainly focused on the characterization of the primary lesional substrate, while whole-brain investigations remain scarce. Our purpose was to assess large-scale brain organization in prevalent cortical malformations. Based on experimental evidence suggesting that distributed effects of focal insults are modulated by stages of brain development, we postulated differential patterns of network anomalies across subtypes of malformations. We studied a cohort of patients with focal cortical dysplasia type II (n = 63), subcortical nodular heterotopia (n = 44), and polymicrogyria (n = 34), and compared them to 82 age- and sex-matched controls. Graph theoretical analysis of structural covariance networks indicated a consistent rearrangement towards a regularized architecture characterized by increased path length and clustering, as well as disrupted rich-club topology, overall suggestive of inefficient global and excessive local connectivity. Notably, we observed a gradual shift in network reconfigurations across subgroups, with only subtle changes in focal cortical dysplasia type II, moderate effects in heterotopia and maximal effects in polymicrogyria. Analysis of resting state functional connectivity also revealed gradual network changes, with most marked rearrangement in polymicrogyria; contrary to findings in the structural domain, however, functional architecture was characterized by decreases in both local and global parameters. Diverging results in the structural and functional domain were supported by formal structure-function coupling analysis. Our findings support the concept that time of insult during corticogenesis impacts the severity of topological network reconfiguration. Specifically, late-stage malformations, typified by polymicrogyria, may selectively disrupt the formation of large-scale cortico-cortical networks and thus lead to a more profound impact on whole-brain organization than early stage disturbances of predominantly radial migration patterns observed in cortical dysplasia type II, which likely affect a relatively confined cortical territory.

Region-specific connectivity in patients with periventricular nodular heterotopia and epilepsy: A study combining diffusion tensor imaging and functional MRI.

OBJECTIVES: Periventricular nodular heterotopia (PNH) is an important cause of chronic epilepsy. The purpose of this study was to evaluate region-specific connectivity in PNH patients with epilepsy and assess correlation between connectivity strength and clinical factors including duration and prognosis. METHODS: Diffusion tensor imaging (DTI) and resting state functional MRI (fMRI) were performed in 28 subjects (mean age 27.4years; range 9-56years). The structural connectivity of fiber bundles passing through the manually-selected segmented nodules and other brain regions were analyzed by tractography. Cortical lobes showing functional correlations to nodules were also determined. RESULTS: For all heterotopic gray matter nodules, including at least one in each subject, the most frequent segments to which nodular heterotopia showed structural (132/151) and functional (146/151) connectivity were discrete regions of the ipsilateral overlying cortex. Agreement between diffusion tensor tractography and functional connectivity analyses was conserved in 81% of all nodules (122/151). In patients with longer duration or refractory epilepsy, the connectivity was significantly stronger, particularly to the frontal and temporal lobes (P<0.05). CONCLUSIONS: Nodules in PNH were structurally and functionally connected to the cortex. The extent is stronger in patients with longstanding or intractable epilepsy. These findings suggest the region-specific interactions may help better evaluate prognosis and seek medical or surgical interventions of PNH-related epilepsy.

Llgl1 Connects Cell Polarity with Cell-Cell Adhesion in Embryonic Neural Stem Cells.

Malformations of the cerebral cortex (MCCs) are devastating developmental disorders. We report here that mice with embryonic neural stem-cell-specific deletion of Llgl1 (Nestin-Cre/Llgl1fl/fl), a mammalian ortholog of the Drosophila cell polarity gene lgl, exhibit MCCs resembling severe periventricular heterotopia (PH). Immunohistochemical analyses and live cortical imaging of PH formation revealed that disruption of apical junctional complexes (AJCs) was responsible for PH in Nestin-Cre/Llgl1fl/fl brains. While it is well known that cell polarity proteins govern the formation of AJCs, the exact mechanisms remain unclear. We show that LLGL1 directly binds to and promotes internalization of N-cadherin, and N-cadherin/LLGL1 interaction is inhibited by atypical protein kinase C-mediated phosphorylation of LLGL1, restricting the accumulation of AJCs to the basolateral-apical boundary. Disruption of the N-cadherin-LLGL1 interaction during cortical development in vivo is sufficient for PH. These findings reveal a mechanism responsible for the physical and functional connection between cell polarity and cell-cell adhesion machineries in mammalian cells.

Periventricular Nodular Heterotopia: Detection of Abnormal Microanatomic Fiber Structures with Whole-Brain Diffusion MR Imaging Tractography.

Purpose To investigate whether it is possible in patients with periventricular nodular heterotopia (PVNH) to detect abnormal fiber projections that have only previously been reported in the histopathology literature. Materials and Methods Whole-brain diffusion-weighted (DW) imaging data from 14 patients with bilateral PVNH and 14 age- and sex-matched healthy control subjects were prospectively acquired by using 3.0-T magnetic resonance (MR) imaging between August 1, 2008, and December 5, 2012. All participants provided written informed consent. The DW imaging data were processed to generate whole-brain constrained spherical deconvolution (CSD)-based tractography data and super-resolution track-density imaging (TDI) maps. The tractography data were overlaid on coregistered three-dimensional T1-weighted images to visually assess regions of heterotopia. A panel of MR imaging researchers independently assessed each case and indicated numerically (no = 1, yes = 2) as to the presence of abnormal fiber tracks in nodular tissue. The Fleiss κ statistical measure was applied to assess the reader agreement. Results Abnormal fiber tracks emanating from one or more regions of heterotopia were reported by all four readers in all 14 patients with PVNH (Fleiss κ = 1). These abnormal structures were not visible on the tractography data from any of the control subjects and were not discernable on the conventional T1-weighted images of the patients with PVNH. Conclusion Whole-brain CSD-based fiber tractography and super-resolution TDI mapping reveals abnormal fiber projections in nodular tissue suggestive of abnormal organization of white matter (with abnormal fibers both within nodules and projecting to the surrounding white matter) in patients with bilateral PVNH. © RSNA, 2016.

Clinical and neuroimaging findings in children with gray matter heterotopias: A single institution experience of 36 patients.

OBJECTIVE: To describe the clinical spectrum and neuroimaging features of childhood gray matter heterotopias in a single tertiary hospital in Taiwan. METHODS: We retrospectively reviewed the medical records and magnetic resonance images (MRI) of 36 patients with gray matter heterotopias, 19 females and 17 males, between July 1999 and June 2014. The MRI morphologic findings of gray matter heterotopias were recorded along with the presence of associated cerebral malformations. The clinical, electrophysiological and associated systemic malformation data were also recorded. RESULTS: A total of 36 patients were included in the study. Their ages ranged from 1 month to 18 years with a mean age of 3 years 6 months. According to the location of gray matter heterotopias, patients were classified into two groups: periventricular (26) and band (10). The phenotypic spectrum in our population differed from that described previously. In the periventricular group, additional cerebral malformations were found in 18/26 (69%) and systemic malformations in 14/26 (54%). In the band group, additional cerebral malformations were found in 5/10 (50%) and systemic malformations in 2/10 (20%). The majority of patients had developmental delay and intellectual deficit. Twenty-two patients suffered from epileptic seizures with 12 developing refractory epilepsy. CONCLUSIONS: In periventricular heterotopias, the most common associated cerebral malformation was ventriculomegaly, followed by agenesis of corpus callosum. Congenital heart disease was the most common additional systemic malformation. However, the most common associated cerebral malformation was pachygyria in band form. The majority of patients had developmental delay, intellectual deficit, especially in band heterotopias.

Severe and Progressive Fetal Ventriculomegaly Leading to the Diagnosis of Periventricular Nodular Heterotopias with Good Outcome.

Severe fetal ventriculomegaly is generally associated with poor prognosis in terms of survival and neurodevelopment outcome. As such, many parents opt to terminate the pregnancy independently of a known etiology. We report here the case of a female fetus with severe progressive ventriculomegaly due to the unexpected presence of bilateral nodular periventricular heterotopias visualized on MRI of a fetal brain. Reaching a structural diagnosis was perceived as a relief for the parents and the pregnancy was continued. Neurodevelopment assessment at 3 years of age is normal with no epilepsy.

Phenotypic and imaging features of FLNA-negative patients with bilateral periventricular nodular heterotopia and epilepsy.

PURPOSE: Periventricular nodular heterotopia (PVNH) is a malformation of cortical development due to impaired neuronal migration resulting in the formation of nodular masses of neurons and glial cells in close proximity to the ventricular walls. We report the clinical characteristics of the largest case series of FLNA-negative patients with seizures and bilateral periventricular heterotopia. METHODS: Participants were recruited through the Epilepsy Phenome/Genome Project (EPGP), a multicenter collaborative effort to collect detailed phenotypic data and DNA on a large number of individuals with epilepsy, including a cohort with symptomatic epilepsy related to PVNH. Included subjects had epilepsy, and MRI confirmed bilateral PVNH. Magnetic resonance imaging studies were visually and quantitatively reviewed to investigate the topographic extent of PVNH, symmetry, and laterality. KEY FINDINGS: We analyzed data on 71 patients with bilateral PVNH. The incidence of febrile seizures was 16.6%. There was at least one other family member with epilepsy in 36.9% of this population. Developmental delay was present in 21.8%. Focal onset seizures were the most common type of seizure presentation (79.3%). High heterotopia burden was strongly associated with female gender and trigonal nodular localization. There was no evidence for differences in brain volume between PVNH subjects and controls. No relationship was observed between heterotopic volume and gender, developmental delay, location of PVNH, ventricular or cerebellar abnormalities, laterality of seizure onset, age at seizure onset, and duration of epilepsy. SIGNIFICANCE: A direct correlation was observed between high heterotopia burden, female gender, and trigonal location in this large cohort of FLNA-negative bilateral PVNH patients with epilepsy. Quantitative MRI measurements indicated that this correlation is based on the diffuse nature of the heterotopic nodules rather than on the total volume of abnormal heterotopic tissue.