Sporadic periventricular nodular heterotopia: Classification, phenotype and correlation with Filamin A mutations

Stereo-electroencephalography-guided radiofrequency thermocoagulation restricted to periventricular nodular heterotopias in patients with drug-resistant epilepsy: A single center experience

INTRODUCTION

Periventricular nodular heterotopias (PVNH) are developmental abnormalities with neurons abnormally clustered around the cerebral ventricles. Patients frequently present with focal drug-resistant epilepsy (DRE). However, the relationship between PVNH and the seizure onset zone (SOZ) is complex. Stereo-electroencephalography (SEEG) is an invasive diagnostic procedure for patients with DRE. In selected patients, the SEEG may be converted into a therapeutic procedure, lesioning the probable (SOZ) with pulsed radiofrequency thermocoagulation (RFTC). The aim of our study was to evaluate the efficacy and safety of SEEG-RFTC in a series of DRE patients with PVNH.

METHODS

Twenty-four patients with focal DRE related to PVNH and treated with SEEG-guided-RFTC restricted to nodules were prospectively collected between 2016 and 2023 and retrospectively analyzed after a follow-up of at least 12 months.

RESULTS

Seventeen patients (71 %) responded (ILAE class 1-4) after SEEG-guided RFTC of whom eleven (46 %) became seizure-free (class 1) at last follow up, nine (45 %) despite residual PVNH tissue on MRI. SEEG seizure onset was restricted to PVNH in eleven patients (class 1 in 45 %) and simultaneously in PVNH and other cortical areas in thirteen patients (class 1 in 46 %). Out of 31 SEEG-RFTC procedures in twenty-four patients, adverse events, related to RFTC, were recorded in eight (26 %), of which two patients (8 %) had predicted permanent visual complaints whilst the other five had transient complaints.

SIGNIFICANCE

This study demonstrates that a considerable percentage of patients, even with bilateral, multiple PVNH and involvement of adjacent cortical regions can be rendered seizure-free with SEEG-guided-RFTC restricted to the nodules. Furthermore, this study delivers evidence that the complete destruction of the entire nodule is not necessary to render a patient seizure free. This justifies the use of SEEG in patients with single, multiple or bilateral PVNHs to provide insight into the epileptogenic organization in and around these lesions.

Heterozygous truncating variant of TAOK1 in a boy with periventricular nodular heterotopia: a case report and literature review of TAOK1-related neurodevelopmental disorders

BACKGROUND

Thousand and one amino-acid kinase 1 (TAOK1) encodes the MAP3K protein kinase TAO1, which has recently been displayed to be essential for neuronal maturation and cortical differentiation during early brain development. Heterozygous variants in TAOK1 have been reported in children with neurodevelopmental disorders, with or without macrocephaly, hypotonia and mild dysmorphic traits. Literature reports lack evidence of neuronal migration disorders in TAOK1 patients, although studies in animal models suggest this possibility.

CASE PRESENTATION

We provide a clinical description of a child with a neurodevelopmental disorder due to a novel TAOK1 truncating variant, whose brain magnetic resonance imaging displays periventricular nodular heterotopia.

CONCLUSIONS

To our knowledge, this is the first report of a neuronal migration disorder in a patient with a TAOK1-related neurodevelopmental disorder, thus supporting the hypothesized pathogenic mechanisms of TAOK1 defects.

The phenotypic spectrum of epilepsy associated with periventricular nodular heterotopia

BACKGROUND

Periventricular nodular heterotopia (PVNH) is a congenital brain malformation often associated with seizures. We aimed to clarify the spectrum of epilepsy phenotypes in PVNH and the significance of specific brain malformation patterns.

METHODS

In this retrospective cohort study, we recruited people with PVNH and a history of seizures, and collected data via medical record review and a standardized questionnaire.

RESULTS

One hundred individuals were included, aged 1 month to 61 years. Mean seizure onset age was 7.9 years. Ten patients had a self-limited epilepsy course and 35 more were pharmacoresponsive. Fifty-five had ongoing seizures, of whom 23 met criteria for drug resistance. Patients were subdivided as follows: isolated PVNH ("PVNH-Only") single nodule (18) or multiple nodules (21) and PVNH with additional brain malformations ("PVNH-Plus") single nodule (8) or multiple nodules (53). Of PVNH-Only single nodule, none had drug-resistant seizures. Amongst PVNH-Plus, 55% with multiple unilateral nodules were pharmacoresponsive, compared to only 21% with bilateral nodules. PVNH-Plus with bilateral nodules demonstrated the highest proportion of drug resistance (39%). A review of genetic testing results revealed eight patients with pathogenic or likely pathogenic single-gene variants, two of which were FLNA. Five had copy number variants, two of which were pathogenic.

CONCLUSIONS

The spectrum of epilepsy phenotypes in PVNH is broad, and seizure patterns are variable; however, epilepsy course may be predicted to an extent by the pattern of malformation. Overall, drug-resistant epilepsy occurs in approximately one quarter of affected individuals. When identified, genetic etiologies are very heterogeneous.

Computational analysis of missense filamin-A variants, including the novel p.Arg484Gln variant of two brothers with periventricular nodular heterotopia

Background

Periventricular nodular heterotopia (PNH) is a cell migration disorder associated with mutations in Filamin-A (FLNA) gene on chromosome X. Majority of the individuals with PNH-associated FLNA mutations are female whereas liveborn males with FLNA mutations are very rare. Fetal viability of the males seems to depend on the severity of the variant. Splicing or severe truncations presumed loss of function of the protein product, lead to male lethality and only partial-loss-of-function variants are reported in surviving males. Those variants mostly manifest milder clinical phenotypes in females and thus avoid detection of the disease in females.

Methods

We describe a novel p.Arg484Gln variant in the FLNA gene by performing whole exome analysis on the index case, his one affected brother and his healthy non-consanguineous parents. The transmission of PNH from a clinically asymptomatic mother to two sons is reported in a fully penetrant classical X-linked dominant mode. The variant was verified via Sanger sequencing. Additionally, we investigated the impact of missense mutations reported in affected males on the FLNa protein structure, dynamics and interactions by performing molecular dynamics (MD) simulations to examine the disease etiology and possible compensative mechanisms allowing survival of the males.

Results

We observed that p.Arg484Gln disrupts the FLNa by altering its structural and dynamical properties including the flexibility of certain regions, interactions within the protein, and conformational landscape of FLNa. However, these impacts existed for only a part the MD trajectories and highly similar patterns observed in the other 12 mutations reported in the liveborn males validated this mechanism.

Conclusion

It is concluded that the variants seen in the liveborn males result in transient pathogenic effects, rather than persistent impairments. By this way, the protein could retain its function occasionally and results in the survival of the males besides causing the disease.

Haploinsufficiency of ARFGEF1 is associated with developmental delay, intellectual disability, and epilepsy with variable expressivity

PURPOSE

ADP ribosylation factor guanine nucleotide exchange factors (ARFGEFs) are a family of proteins implicated in cellular trafficking between the Golgi apparatus and the plasma membrane through vesicle formation. Among them is ARFGEF1/BIG1, a protein involved in axon elongation, neurite development, and polarization processes. ARFGEF1 has been previously suggested as a candidate gene for different types of epilepsies, although its implication in human disease has not been well characterized.

METHODS

International data sharing, in silico predictions, and in vitro assays with minigene study, western blot analyses, and RNA sequencing.

RESULTS

We identified 13 individuals with heterozygous likely pathogenic variants in ARFGEF1. These individuals displayed congruent clinical features of developmental delay, behavioral problems, abnormal findings on brain magnetic resonance image (MRI), and epilepsy for almost half of them. While nearly half of the cohort carried de novo variants, at least 40% of variants were inherited from mildly affected parents who were clinically re-evaluated by reverse phenotyping. Our in silico predictions and in vitro assays support the contention that ARFGEF1-related conditions are caused by haploinsufficiency, and are transmitted in an autosomal dominant fashion with variable expressivity.

CONCLUSION

We provide evidence that loss-of-function variants in ARFGEF1 are implicated in sporadic and familial cases of developmental delay with or without epilepsy.

Resting-state functional connectivity alterations in periventricular nodular heterotopia related epilepsy

Periventricular nodular heterotopia (PNH) is a neural migration disorder which often presents clinically with seizures. However, the underlying functional neural basis of PNH is still unclear. We aimed to explore the underlying pathological mechanism of PNH by combining both whole brain functional connectivity (FC) and seed-based FC analyses. We utilized resting-state fMRI to measure functional connectivity strength (FCS) in 38 patients with PNH-related epilepsy and 38 control subjects. The regions with FCS alterations were selected as seeds in the following FC analyses. Pearson correlation analyses were performed to explore associations between these functional neural correlates and clinical features. In comparison with controls, PNH patients showed lower FCS in bilateral insula (P < 0.05, family wise error (FWE) correction), higher FC in the default mode network and lower FC in the fronto-limbic-cerebellar circuits (P < 0.05, FWE correction). Pearson correlation analyses revealed that FCS in bilateral insula was negatively correlated with the epilepsy duration (P < 0.05); medial prefronto-insular connectivity was negatively correlated with Hamilton Anxiety Scale (P < 0.05) and cerebellar-insular connectivity was also negatively correlated with Hamilton Depression Scale (P < 0.05). Using the resting-state FCS analytical approach, we identified significant insular hypoactivation in PNH patients, which suggests that the insula might represent the cortical hub of the whole-brain networks in this condition. Additionally, disruption of resting state FC in large-scale neural networks pointed to a connectivity-based neuropathological process in PNH.

A somatic mutation in MEN1 gene detected in periventricular nodular heterotopia tissue obtained from depth electrodes

Periventricular nodular heterotopia (PNH) is a common structural malformation of cortical development. Mutations in the filamin A gene are frequent in familial cases with X‐linked PNH. However, many cases with sporadic PNH remain genetically unexplained. Although medically refractory epilepsy often brings attention to the underlying PNH, patients are often not candidates for surgical resection. This limits access to neuronal tissue harboring causal mutations. We evaluated a patient with PNH and medically refractory focal epilepsy who underwent a presurgical evaluation with stereotactically placed electroencephalographic (SEEG) depth electrodes. Following SEEG explantation, we collected trace tissue adherent to the electrodes and extracted the DNA. Whole‐exome sequencing performed in a Clinical Laboratory Improvement Amendments–approved genetic diagnostic laboratory uncovered a de novo heterozygous pathogenic variant in novel candidate PNH gene MEN1 (multiple endocrine neoplasia type 1; c.1546dupC, p.R516PfsX15). The variant was absent in an earlier exome profiling of the venous blood–derived DNA. The MEN1 gene encodes the ubiquitously expressed, nuclear scaffold protein menin, a known tumor suppressor gene with an established role in the regulation of transcription, proliferation, differentiation, and genomic integrity. Our study contributes a novel candidate gene in PNH generation and a novel practical approach that integrates electrophysiological and genetic explorations of epilepsy.

FLNA mutations in surviving males presenting with connective tissue findings: two new case reports and review of the literature

Background

Mutations in the X-linked gene filamin A (FLNA), encoding the actin-binding protein FLNA, cause a wide spectrum of connective tissue, skeletal, cardiovascular and/or gastrointestinal manifestations. Males are typically more severely affected than females with common pre- or perinatal death.

Case presentation

We provide a genotype- and phenotype-oriented literature overview of FLNA hemizygous mutations and report on two live-born male FLNA mutation carriers. Firstly, we identified a de novo, missense mutation (c.238C > G, p.(Leu80Val)) in a five-year old Indian boy who presented with periventricular nodular heterotopia, increased skin laxity, joint hypermobility, mitral valve prolapse with regurgitation and marked facial features (e.g. a flat face, orbital fullness, upslanting palpebral fissures and low-set ears). Secondly, we identified two cis-located FLNA mutations (c.7921C > G, p.(Pro2641Ala); c.7923delC, p.(Tyr2642Thrfs*63)) in a Bosnian patient with Ehlers-Danlos syndrome-like features such as skin translucency and joint hypermobility. This patient also presented with brain anomalies, pectus excavatum, mitral valve prolapse, pulmonary hypertension and dilatation of the pulmonary arteries. He died from heart failure in his second year of life.

Conclusions

These two new cases expand the list of live-born FLNA mutation-positive males with connective tissue disease from eight to ten, contributing to a better knowledge of the genetic and phenotypic spectrum of FLNA-related disease.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0655-0) contains supplementary material, which is available to authorized users.

Recent Developments in Using Drosophila as a Model for Human Genetic Disease

Many insights into human disease have been built on experimental results in Drosophila, and research in fruit flies is often justified on the basis of its predictive value for questions related to human health. Additionally, there is now a growing recognition of the value of Drosophila for the study of rare human genetic diseases, either as a means of validating the causative nature of a candidate genetic variant found in patients, or as a means of obtaining functional information about a novel disease-linked gene when there is little known about it. For these reasons, funders in the US, Europe, and Canada have launched targeted programs to link human geneticists working on discovering new rare disease loci with researchers who work on the counterpart genes in Drosophila and other model organisms. Several of these initiatives are described here, as are a number of output publications that validate this new approach.

Identification of a novel synaptic protein, TMTC3, involved in periventricular nodular heterotopia with intellectual disability and epilepsy

Defects in neuronal migration cause brain malformations, which are associated with intellectual disability (ID) and epilepsy. Using exome sequencing, we identified compound heterozygous variants (p.Arg71His and p. Leu729ThrfsTer6) in TMTC3, encoding transmembrane and tetratricopeptide repeat containing 3, in four siblings with nocturnal seizures and ID. Three of the four siblings have periventricular nodular heterotopia (PVNH), a common brain malformation caused by failure of neurons to migrate from the ventricular zone to the cortex. Expression analysis using patient-derived cells confirmed reduced TMTC3 transcript levels and loss of the TMTC3 protein compared to parental and control cells. As TMTC3 function is currently unexplored in the brain, we gathered support for a neurobiological role for TMTC3 by generating flies with post-mitotic neuron-specific knockdown of the highly conserved Drosophila melanogaster TMTC3 ortholog, CG4050/tmtc3. Neuron-specific knockdown of tmtc3 in flies resulted in increased susceptibility to induced seizures. Importantly, this phenotype was rescued by neuron-specific expression of human TMTC3, suggesting a role for TMTC3 in seizure biology. In addition, we observed co-localization of TMTC3 in the rat brain with vesicular GABA transporter (VGAT), a presynaptic marker for inhibitory synapses. TMTC3 is localized at VGAT positive pre-synaptic terminals and boutons in the rat hypothalamus and piriform cortex, suggesting a role for TMTC3 in the regulation of GABAergic inhibitory synapses. TMTC3 did not co-localize with Vglut2, a presynaptic marker for excitatory neurons. Our data identified TMTC3 as a synaptic protein that is involved in PVNH with ID and epilepsy, in addition to its previously described association with cobblestone lissencephaly.

Integrity of the corpus callosum in patients with periventricular nodular heterotopia related epilepsy by FLNA mutation

Objective

To investigate the quantitative diffusion properties of the corpus callosum (CC) in a large group of patients with periventricular nodular heterotopia (PNH) related epilepsy and to further investigate the effect of Filamin A (FLNA) mutation on these properties.

Methods

Patients with PNH (n = 34), subdivided into FLNA-mutated (n = 11) and FLNA-nonmutated patients (n = 23) and healthy controls (n = 34), underwent 3.0 T structural MRI and diffusion imaging scan (64 direction). Fractional anisotropy (FA) and mean diffusivity (MD) were measured in the three major subdivisions of the CC (genu, body and splenium). Correlations between DTI metric changes and clinical parameters were also evaluated. Furthermore, the effect of FLNA mutation on structural integrity of the corpus callosum was examined.

Results

Patients with PNH and epilepsy had significant reductions in FA for the genu and splenium of the CC, accompanied by increases in MD for the splenium, as compared to healthy controls. There were no correlations between clinical parameters of epilepsy and MD. The FA value in the splenium negatively correlated with epilepsy duration. Interestingly, FLNA-mutated patients showed significantly decreased FA for all three major subdivisions of the CC, and increased MD for the genu and splenium, as compared to HCs and FLNA-nonmutated patients.

Conclusions

These findings support the conclusion that patients with epilepsy secondary to PNH present widespread microstructural changes found in the corpus callosum that extend beyond the macroscopic MRI-visible lesions. This study also indicates that FLNA may affect white matter integrity in this disorder.

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PNH patients presented diffusion abnormality in splenium segment of the CC.

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Only the FA value for the splenium negatively correlated with epilepsy duration.

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In PNH, DTI changes of CC differentiate FLNA-mutated from nonmutated subjects.