A developmental and genetic classification for malformations of cortical development: update 2012

Circuit Mechanisms Underlying Epileptogenesis in a Mouse Model of Focal Cortical Malformation

The way in which aberrant neural circuits contribute to epilepsy remains unclear. To elucidate this question, we dissected the circuit mechanisms underlying epileptogenesis using a mouse model of focal cortical malformation with spontaneous epileptiform discharges. We found that spontaneous spike-wave discharges and optogenetically induced hyperexcitable bursts in vivo were present in a cortical region distal to (>0.7 mm) freeze-lesion-induced microgyrus, instead of near the microgyrus. ChR2-assisted circuit mapping revealed ectopic inter-laminar excitatory input from infragranular layers to layers 2/3 pyramidal neurons as the key component of hyperexcitable circuitry. This hyperactivity disrupted the balance between excitation and inhibition and was more prominent in the cortical region distal to the microgyrus. Consistently, the inhibition from both parvalbumin-positive interneurons (PV) and somatostatin-positive interneurons (SOM) to pyramidal neurons were altered in a layer- and site-specific fashion. Finally, closed-loop optogenetic stimulation of SOM, but not PV, terminated spontaneous spike-wave discharges. Together, these results demonstrate the occurrence of highly site- and cell-type-specific synaptic reorganization underlying epileptic cortical circuits and provide new insights into potential treatment strategies.

Electrographic pattern recognition: A simple tool to predict clinical outcome in children with lissencephaly

PURPOSE

To describe and correlate the clinical, radiological and EEG findings in children with lissencephaly.

METHOD

Retrospective record analysis of children with lissencephaly presenting to tertiary health centre in Northern India was performed. Radiological classification and severity scoring were done. EEG findings were categorized into three patterns and its association with clinical severity was studied.

RESULTS

Twenty-eight children (males = 17) with lissencephaly were enrolled. Median age at diagnosis was 6.5months (range 3days-3years). Global developmental delay (median social quotient (SQ) = 25 (range15-68) was seen in all; motor deficits in 23 (82 %); epilepsy in 21 (75 %); behavioural problems in 18 (64 %); ophthalmic problems in 17 (61 %); microcephaly in 13 (46 %); feeding difficulty in 12 (43 %). Radiologically, classical Type I lissencephaly was seen in 18(64 %), cobblestone variant (Type II) in 5 (18 %) and microlissencephaly in 5 (18 %). Grade 4 (diffuse pachygyria) radiologic severity was most common (severity grade 1-6); no cases with severity score 5 or 6 were seen. The clinical profile did not correspond with radiological severity grading. EEG pattern recognition revealed pattern I in 14 (50 %); pattern II in 6 (21 %); pattern III in 8 (29 %). Children with pattern III EEG had drug resistant epilepsy and severe developmental delay. No relationship between EEG patterns and radiological severity grading was evident.

CONCLUSION

EEG is better predictor of clinical status and outcome rather than radiological severity grading. EEG pattern III is associated with severe developmental delay and drug resistant epilepsy.

Treatment of Epilepsy Associated with Periventricular Nodular Heterotopia

PURPOSE OF REVIEW

Epilepsy associated with periventricular nodular heterotopia (PNH), a developmental malformation, is frequently drug-resistant and requires focal therapeutic intervention. Invasive EEG study is usually necessary to delineate the epileptogenic zone, but constructing an accurate hypothesis to define an appropriate electrode implantation scheme and the treatment is challenging. This article reviews recent studies that help understanding the epileptogenicity and potential therapeutic options in PNH.

RECENT FINDINGS

New noninvasive diagnostic and intracerebral EEG analytic tools demonstrated that cortical hyperexcitability and aberrant connectivity (between nodules and cortices and among nodules) are likely mechanisms causing epilepsy in most patients. The deeply seated PNH, if epileptogenic, are ideal target for stereotactic ablative techniques, which offer concomitant ablation of multiple regions with relatively satisfactory seizure outcome. Advance in diagnostic and analytic tools have enhanced our understanding of the complex epileptogenicity in PNH. Development in stereotactic ablative techniques now offers promising therapeutic options for these patients.

[Surgical treatment of epilepsy in children with focal cortical dysplasia]

OBJECTIVE

Surgery is the first-line treatment option in children with FCD and refractory epilepsy, but the rate of success and patient numbers who became free of seizures vary widely from series to series.

STUDY AIMS

To elicit variables affecting the outcome and predicting achievement of the long-term seizure-free status.

MATERIAL AND METHODS

One hundred sixty-nine children with cortical dysplasia and DR-epilepsy underwent surgery Preoperative evaluation included prolonged video-EEG and MRI (in all patients) and neuropsychological testing when possible. Fourteen patients underwent invasive EEG, fMRI and MEG were used also in some cases. Including 27 repeat procedures the list of overall 196 surgeries performed consists of: cortectomy (lesionectomy with or without adjacent epileptogenic cortices) – in 116 cases; lobectomy – in 46; and various disconnective procedures – in 34 patients. Almost routinely employed intraoperative ECOG (134 surgeries) was combined with stimulation and/or SSEP in 47 cases to map eloquent cortex (with CST-tracking in some). A new permanent and not anticipated neurological deficit developed post-surgery in 5 cases (2,5%). Patients were follow-upped using video-EEG and MRI and FU which lasts more than 2 years (median – 3 years) is known in 56 cases. Thirty-two children were free of seizures at the last check (57,2% rate of Engel IA). A list of variables regarding patients’ demography, seizure type, lesion pathology and localization, and those related to surgery and its extent were evaluated to figure out anyone associated with favorable outcome.

RESULTS

Both Type II FCDs and their anatomically complete excision are positive predictors for favorable outcome and achievement of SF-status (p<0,05). Residual epileptic activity on immediate post-resection ECOG do not affect the outcome.

CONCLUSION

Patients with Type II FCD, particularly with Type IIb malformations are the best candidates for curative surgery, including cases with lesions in brain eloquent areas. Kids with Type I FCD have much less chances to become free of seizures when attempting focal cortectomy. However, some of them with early onset catastrophic epilepsies may benefit from larger surgeries using lobectomy or various disconnections.

Neuronal migration and disorders - an update

This review highlights genes, proteins and subcellular mechanisms, recently shown to influence cortical neuronal migration. A current view on mechanisms which become disrupted in a diverse array of migration disorders is presented. The microtubule (MT) cytoskeleton is a major player in migrating neurons. Recently, variable impacts on MTs have been revealed in different cell compartments. Thus there are a multiplicity of effects involving centrosomal, microtubule-associated, as well as motor proteins. However, other causative factors also emerge, illuminating cortical neuronal migration research. These include disruptions of the actin cytoskeleton, the extracellular matrix, different adhesion molecules and signaling pathways, especially revealed in disorders such as periventricular heterotopia. These recent advances often involve the use of human in vitro models as well as model organisms. Focusing on cell-type specific knockouts and knockins, as well as generating omics and functional data, all seem critical for an integrated view on neuronal migration dysfunction.

Changes of EEG spectra in rat brains with different patterns of dysplasia in response to pilocarpine-induced seizures

Disorders of neurogenesis at early developmental stages lead to irreversible structural and functional impairments of the brain. As further their consequences, increases in brain excitability and the development of drug-resistant epilepsy can frequently be observed in clinical cases. Mechanisms underlying these phenomena can also be examined on animal models of brain dysplasia. This study was conducted on rats with four degrees of brain dysplasia following exposure to gamma radiation on days 13, 15, 17, or 19 of prenatal development. When reached adulthood, the rats received electroencephalographic (EEG) transmitter implantation. Thereafter, pilocarpine was administered, and significant differences in susceptibility to seizures were detected depending on the degree of brain dysplasia. Before, during, and after the seizures, EEG was recorded in free moving animals. Additionally, the intensity of seizure behavioral symptoms was assessed. Strong and moderate correlations were found between the intensity of seizure behavioral symptoms, the power of particular EEG bands, and volumes of dysplastic brains and their regions. The data drew particular attention to correlations between variations in EEG spectra and changes in the midbrain and pons volumes. The results point to possible significant roles of these regions in the observed changes of susceptibility to seizures. Consequently, the frequently used experimental model was considered here not only as representing cases of cortical dysplasia but also of generalized, diffuse dysplasia of the whole brain.

Periventricular Venous Infarction in an Extremely Premature Infant as the Cause of Schizencephaly

Schizencephaly is a disorder of neuronal migration which has been hypothesized to arise from vascular ischemic lesion during the early phase of neuroembryogenesis. We describe a case of a premature boy born at 23 weeks of gestation with neonatal stroke. On the first day of life cranial ultrasonography detected a grade II intraventricular hemorrhage and on day 12 periventricular venous infarction. At the postconceptional age of 40 weeks, magnetic resonance imaging revealed a gray matter–lined cleft, suggesting schizencephaly. We have evidence of the pathogenesis of schizencephaly following vascular ischemic stroke early in neurodevelopment before neuronal migration is completed.

Repression of Irs2 by let-7 miRNAs is essential for homeostasis of the telencephalic neuroepithelium

Structural integrity and cellular homeostasis of the embryonic stem cell niche are critical for normal tissue development. In the telencephalic neuroepithelium, this is controlled in part by cell adhesion molecules and regulators of progenitor cell lineage, but the specific orchestration of these processes remains unknown. Here, we studied the role of microRNAs in the embryonic telencephalon as key regulators of gene expression. By using the early recombiner Rx-Cre mouse, we identify novel and critical roles of miRNAs in early brain development, demonstrating they are essential to preserve the cellular homeostasis and structural integrity of the telencephalic neuroepithelium. We show that Rx-Cre;Dicer^F/F mouse embryos have a severe disruption of the telencephalic apical junction belt, followed by invagination of the ventricular surface and formation of hyperproliferative rosettes. Transcriptome analyses and functional experiments in vivo show that these defects result from upregulation of Irs2 upon loss of let-7 miRNAs in an apoptosis-independent manner. Our results reveal an unprecedented relevance of miRNAs in early forebrain development, with potential mechanistic implications in pediatric brain cancer.

The Heritability of Cortical Folding: Evidence from the Human Connectome Project

The mechanisms underlying cortical folding are incompletely understood. Prior studies have suggested that individual differences in sulcal depth are genetically mediated, with deeper and ontologically older sulci more heritable than others. In this study, we examine FreeSurfer-derived estimates of average convexity and mean curvature as proxy measures of cortical folding patterns using a large (N = 1096) genetically informative young adult subsample of the Human Connectome Project. Both measures were significantly heritable near major sulci and primary fissures, where approximately half of individual differences could be attributed to genetic factors. Genetic influences near higher order gyri and sulci were substantially lower and largely nonsignificant. Spatial permutation analysis found that heritability patterns were significantly anticorrelated to maps of evolutionary and neurodevelopmental expansion. We also found strong phenotypic correlations between average convexity, curvature, and several common surface metrics (cortical thickness, surface area, and cortical myelination). However, quantitative genetic models suggest that correlations between these metrics are largely driven by nongenetic factors. These findings not only further our understanding of the neurobiology of gyrification, but have pragmatic implications for the interpretation of heritability maps based on automated surface-based measurements.

Correlating Neuroimaging and CNVs Data: 7 Years of Cytogenomic Microarray Analysis on Patients Affected by Neurodevelopmental Disorders

The aim of this study was to evaluate the relationship between neurodevelopmental disorders, brain anomalies, and copy number variations (CNVs) and to estimate the diagnostic potential of cytogenomical microarray analysis (CMA) in individuals neuroradiologically characterized with intellectual developmental disorders (IDDs) isolated or associated with autism spectrum disorders (ASDs) and epilepsy (EPI), all of which were identified as a "synaptopathies." We selected patients who received CMA and brain magnetic resonance imaging (MRI) over a 7-year period. We divided them into four subgroups: IDD, IDD + ASD, IDD + EPI, and IDD + ASD + EPI. The diagnostic threshold of CMA was 16%. The lowest detection rate for both CMA and brain anomalies was found in IDD + ASD, while MRI was significantly higher in IDD and IDD + EPI subgroups. CMA detection rate was significantly higher in patients with brain anomalies, so CMA may be even more appropriate in patients with pathological MRI, increasing the diagnostic value of the test. Conversely, positive CMA in IDD patients should require an MRI assessment, which is more often associated with brain anomalies. Posterior fossa anomalies, both isolated and associated with other brain anomalies, showed a significantly higher rate of CMA positive results and of pathogenic CNVs. In the next-generation sequencing era, our study confirms once again the relevant diagnostic output of CMA in patients with IDD, either isolated or associated with other comorbidities. Since more than half of the patients presented brain anomalies in this study, we propose that neuroimaging should be performed in such cases, particularly in the presence of genomic imbalances.

International consensus recommendations on the diagnostic work-up for malformations of cortical development

Malformations of cortical development (MCDs) are neurodevelopmental disorders that result from abnormal development of the cerebral cortex in utero. MCDs place a substantial burden on affected individuals, their families and societies worldwide, as these individuals can experience lifelong drug-resistant epilepsy, cerebral palsy, feeding difficulties, intellectual disability and other neurological and behavioural anomalies. The diagnostic pathway for MCDs is complex owing to wide variations in presentation and aetiology, thereby hampering timely and adequate management. In this article, the international MCD network Neuro-MIG provides consensus recommendations to aid both expert and non-expert clinicians in the diagnostic work-up of MCDs with the aim of improving patient management worldwide. We reviewed the literature on clinical presentation, aetiology and diagnostic approaches for the main MCD subtypes and collected data on current practices and recommendations from clinicians and diagnostic laboratories within Neuro-MIG. We reached consensus by 42 professionals from 20 countries, using expert discussions and a Delphi consensus process. We present a diagnostic workflow that can be applied to any individual with MCD and a comprehensive list of MCD-related genes with their associated phenotypes. The workflow is designed to maximize the diagnostic yield and increase the number of patients receiving personalized care and counselling on prognosis and recurrence risk.

Delayed Functional Networks Development and Altered Fast Oscillation Dynamics in a Rat Model of Cortical Malformation

Malformations of cortical development (MCD) is associated with a wide range of developmental delay and drug resistant epilepsy in children. By using resting-state functional magnetic resonance imaging (RS-fMRI) and event-related spectral perturbation (ERSP) of cortical electroencephalography (EEG) data, we tried to investigate the neural changes of spatiotemporal functional connectivity (FC) and fast oscillation (FO) dynamics in a rat model of methylazoxymethanol (MAM)-induced MCD. A total of 28 infant rats with prenatal exposure to MAM and those of age matched 28 controls with prenatal saline exposure were used. RS-fMRI were acquired at postnatal day 15 (P15) and 29 (P29), and correlation coefficient analysis of eleven region of interests (ROI) was done to find the differences of functional networks between four groups. Two hour-cortical EEGs were also recorded at P15 and P29 and the ERSP of gamma (30–80 Hz) and ripples (80–200 Hz) were analyzed. The rats with MCD showed significantly delayed development of superior colliculus-brainstem network compared to control rats at P15. In contrast to marked maturation of default mode network (DMN) in controls from P15 to P29, there was no clear development in MCD rats. The MCD rats showed significantly higher cortical gamma and ripples-ERSP at P15 and lower cortical ripples-ERSP at P29 than those of control rats. This study demonstrated delayed development of FC and altered cortical FO dynamics in rats with malformed brain. The results should be further investigated in terms of the epileptogenesis and cognitive dysfunction in patients with MCD.

Microcephalic osteodysplastic primordial dwarfism type II and pachygyria: Morphometric analysis in a 2-year-old girl

Microcephalic osteodysplastic primordial dwarfism (MOPD) type II is a rare disorder characterized by skeletal dysplasia, severe proportionate short stature, insulin resistance and cerebrovascular abnormalities including cerebral aneurysms and moyamoya disease. MOPD type II is caused by mutations in the pericentrin (PCNT) gene, which encodes a protein involved in centrosomes function. We report a 2 year old girl affected by MOPD type II caused by two compound heterozygous loss-of-function variants in PCNT gene, of which one is a novel variant (c.5304delT; p.Gly1769AlafsTer34). The patient presented atypical brain magnetic resonance imaging (MRI) findings consistent with pachygyria. This was confirmed by morphometric analysis of cortical thickness (CT) and gyrification index by comparing MRI data of the patient with a group of eight age-matched healthy controls. The statistical analysis revealed a significant and diffuse increase of CT with an anterior-predominant pattern and diffuse reduced gyrification (p < .05). These findings provide new evidences to the emergent concept that malformations of cortical development are complex disorders and that new genetic findings contribute to the fading of classification borders.

Characterizing White Matter Tract Organization in Polymicrogyria and Lissencephaly: A Multifiber Diffusion MRI Modeling and Tractography Study

BACKGROUND AND PURPOSE

Polymicrogyria and lissencephaly may be associated with abnormal organization of the undelying white matter tracts that have been rarely investigated so far. Our aim was to characterize white matter tract organization in polymicrogyria and lissencephaly using constrained spherical deconvolution, a multifiber diffusion MR imaging modeling technique for white matter tractography reconstruction.

MATERIALS AND METHODS

We retrospectively reviewed 50 patients (mean age, 8.3 ± 5.4 years; range, 1.4-21.2 years; 27 males) with different polymicrogyria (n = 42) and lissencephaly (n = 8) subtypes. The fiber direction-encoded color maps and 6 different white matter tracts reconstructed from each patient were visually compared with corresponding images reconstructed from 7 age-matched, healthy control WM templates. Each white matter tract was assessed by 2 experienced pediatric neuroradiologists and scored in consensus on the basis of the severity of the structural abnormality, ranging from the white matter tracts being absent to thickened. The results were summarized by different polymicrogyria and lissencephaly subgroups.

RESULTS

More abnormal-appearing white matter tracts were identified in patients with lissencephaly compared with those with polymicrogyria (79.2% versus 37.3%). In lissencephaly, structural abnormalities were identified in all studied white matter tracts. In polymicrogyria, the more frequently affected white matter tracts were the cingulum, superior longitudinal fasciculus, inferior longitudinal fasciculus, and optic radiation-posterior corona radiata. The severity of superior longitudinal fasciculus and cingulum abnormalities was associated with the polymicrogyria distribution and extent. A thickened superior fronto-occipital fasciculus was demonstrated in 3 patients.

CONCLUSIONS

We demonstrated a range of white matter tract structural abnormalities in patients with polymicrogyria and lissencephaly. The patterns of white matter tract involvement are related to polymicrogyria and lissencephaly subgroups, distribution, and, possibly, their underlying etiologies.

Transcriptomic Profiling of Ca2+ Transport Systems During the Formation of the Cerebral Cortex in Mice

Cytosolic calcium (Ca²⁺) transients control key neural processes, including neurogenesis, migration, the polarization and growth of neurons, and the establishment and maintenance of synaptic connections. They are thus involved in the development and formation of the neural system. In this study, a publicly available whole transcriptome sequencing (RNA-Seq) dataset was used to examine the expression of genes coding for putative plasma membrane and organellar Ca²⁺-transporting proteins (channels, pumps, exchangers, and transporters) during the formation of the cerebral cortex in mice. Four ages were considered: embryonic days 11 (E11), 13 (E13), and 17 (E17), and post-natal day 1 (PN1). This transcriptomic profiling was also combined with live-cell Ca²⁺ imaging recordings to assess the presence of functional Ca²⁺ transport systems in E13 neurons. The most important Ca²⁺ routes of the cortical wall at the onset of corticogenesis (E11–E13) were TACAN, GluK5, nAChR β2, Cav3.1, Orai3, transient receptor potential cation channel subfamily M member 7 (TRPM7) non-mitochondrial Na⁺/Ca²⁺ exchanger 2 (NCX2), and the connexins CX43/CX45/CX37. Hence, transient receptor potential cation channel mucolipin subfamily member 1 (TRPML1), transmembrane protein 165 (TMEM165), and Ca²⁺ “leak” channels are prominent intracellular Ca²⁺ pathways. The Ca²⁺ pumps sarco/endoplasmic reticulum Ca²⁺ ATPase 2 (SERCA2) and plasma membrane Ca²⁺ ATPase 1 (PMCA1) control the resting basal Ca²⁺ levels. At the end of neurogenesis (E17 and onward), a more numerous and diverse population of Ca²⁺ uptake systems was observed. In addition to the actors listed above, prominent Ca²⁺-conducting systems of the cortical wall emerged, including acid-sensing ion channel 1 (ASIC1), Orai2, P2X2, and GluN1. Altogether, this study provides a detailed view of the pattern of expression of the main actors participating in the import, export, and release of Ca²⁺. This work can serve as a framework for further functional and mechanistic studies on Ca²⁺ signaling during cerebral cortex formation.

Human organoids: model systems for human biology and medicine

The historical reliance of biological research on the use of animal models has sometimes made it challenging to address questions that are specific to the understanding of human biology and disease. But with the advent of human organoids — which are stem cell-derived 3D culture systems — it is now possible to re-create the architecture and physiology of human organs in remarkable detail. Human organoids provide unique opportunities for the study of human disease and complement animal models. Human organoids have been used to study infectious diseases, genetic disorders and cancers through the genetic engineering of human stem cells, as well as directly when organoids are generated from patient biopsy samples. This Review discusses the applications, advantages and disadvantages of human organoids as models of development and disease and outlines the challenges that have to be overcome for organoids to be able to substantially reduce the need for animal experiments.

Human organoids are valuable models for the study of development and disease and for drug discovery, thus complementing traditional animal models. The generation of organoids from patient biopsy samples has enabled researchers to study, for example, infectious diseases, genetic disorders and cancers. This Review discusses the advantages, disadvantages and future challenges of the use of organoids as models for human biology.

Developmental and epileptic encephalopathy due to SZT2 genomic variants: Emerging features of a syndromic condition

Seizure threshold 2 (SZT2) gene mutations have been associated with developmental and epileptic encephalopathies (DEEs). Following a literature review, we collected 22 patients and identified the main clinical features related to SZT2 variants that are epilepsy with onset within the first years of life, intellectual disability (ID), macrocephaly with dysmorphic facial features, corpus callosum (CC) shape abnormalities, and cortical migration disorders. Moreover, we identified the c.7825T>G homozygous missense variant in SZT2 in two female siblings presenting with focal seizures, mild-moderate ID, behavioral disturbances, and facial dysmorphisms. Interictal Electroencephalogram (EEG) and ictal EEG were both informative and revealed, respectively, temporal bilateral asynchronous slow and epileptiform abnormalities and a focal onset in both of them. Neuroimaging study revealed a thick and abnormally shaped CC. Seizure threshold 2 has been identified as a component of the KICSTOR complex, a newly recognized protein complex involved in the mammalian target of rapamycin (mTOR) pathway. mTOR signaling dysregulation represents common pathogenetic mechanisms that can explain the presence of both epileptogenesis and ID. Even if few cases had been reported, a new clinical phenotype is emerging, and recent hypothesis of hyperactivation of mTORC1 signaling might also open to targeted treatments, challenging an early diagnosis as of paramount importance.

Lissencephaly in Shih Tzu dogs

Background

Lissencephaly is a brain malformation characterized by smooth and thickened cerebral surface, which may result in structural epilepsy. Lissencephaly is not common in veterinary medicine. Here, we characterize the first cases of lissencephaly in four Shih Tzu dogs, including clinical presentations and findings of magnetic resonance imaging of lissencephaly and several concomitant brain malformations.

Case presentation

Early-onset acute signs of forebrain abnormalities were observed in all dogs, which were mainly cluster seizures and behavioral alterations. Based on neurological examination, the findings were consistent with symmetrical and bilateral forebrain lesions. Metabolic disorders and inflammatory diseases were excluded. Magnetic resonance imaging for three dogs showed diffuse neocortical agyria and thickened gray matter while one dog had mixed agyria and pachygyria. Other features, such as internal hydrocephalus, supracollicular fluid accumulation, and corpus callosum hypoplasia, were detected concomitantly. Antiepileptic drugs effectively controlled cluster seizures, however, sporadic isolated seizures and signs of forebrain abnormalities, such as behavioral alterations, central blindness, and strabismus persisted.

Conclusions

Lissencephaly should be considered an important differential diagnosis in Shih Tzu dogs presenting with early-onset signs of forebrain abnormalities, including cluster seizures and behavioral alterations. Magnetic resonance imaging was appropriate for ante-mortem diagnosis of lissencephaly and associated cerebral anomalies.

Phenotype description in KIF5C gene hot-spot mutations responsible for malformations of cortical development (MCD)

Malformations of cortical development (MCD) represent a large group of brain cortical anomalies characterized by distinctive MRI findings. This 'radiologically-based' classification required re evaluation over time on identified underlying mechanisms (cytogenetic and/or molecular). The understanding of genotype findings (nature of cytogenetic/molecular mutation, cellular pathways consequences, timing, …) draw line of evidence on these distinctive group of conditions whereas sometimes precise and constant recurrent genotype/phenotype correlation may not be present. The clinical diagnosis of MCD is often difficult due to variability and rarity of individual types of malformations. Recent studies have established a relationship between lissencephaly and pathogenic variants in genes involved in the kinesin/tubulin pathways, as the KIF5C gene. Pathogenic variants in the KIF5C gene are a more recently discovered cause of severe developmental delay with epilepsy, characterized by specific malformation of cortical development such as pachygyria. Only seven children have been described to date. We report the natural history of a sixteen years old patient identified carrier of a KIF5C gene mutation who developed infantile epilepsy. We then gather phenotype description and molecular results of all reported patients so far in order to better define this entity.

NR2F1 regulates regional progenitor dynamics in the mouse neocortex and cortical gyrification in BBSOAS patients

The relationships between impaired cortical development and consequent malformations in neurodevelopmental disorders, as well as the genes implicated in these processes, are not fully elucidated to date. In this study, we report six novel cases of patients affected by BBSOAS (Boonstra‐Bosch‐Schaff optic atrophy syndrome), a newly emerging rare neurodevelopmental disorder, caused by loss‐of‐function mutations of the transcriptional regulator NR2F1. Young patients with NR2F1 haploinsufficiency display mild to moderate intellectual disability and show reproducible polymicrogyria‐like brain malformations in the parietal and occipital cortex. Using a recently established BBSOAS mouse model, we found that Nr2f1 regionally controls long‐term self‐renewal of neural progenitor cells via modulation of cell cycle genes and key cortical development master genes, such as Pax6. In the human fetal cortex, distinct NR2F1 expression levels encompass gyri and sulci and correlate with local degrees of neurogenic activity. In addition, reduced NR2F1 levels in cerebral organoids affect neurogenesis and PAX6 expression. We propose NR2F1 as an area‐specific regulator of mouse and human brain morphology and a novel causative gene of abnormal gyrification.

In vivo MRI Successfully Reveals the Malformation of Cortical Development in Infant Rats

Objective: Malformations of cortical development (MCDs) are major causes of intractable epilepsies. To characterize the early neuroimaging findings of MCDs, we tried to identify the MRI features consistent with pathological findings in an infant rat MCD model, prenatally exposed to methylazoxymethanol (MAM), by using newly developed MRI techniques. Methods: At gestational day 15, two doses of MAM (15 mg/kg intraperitoneally) or normal saline were injected into pregnant rats. The offspring underwent in vivo MRI, including glutamate chemical exchange saturation transfer (GluCEST), ¹H-MR spectroscopy, and diffusion tensor imaging, at postnatal day (P) 15 using a 7T small-animal imaging system. Another set of prenatally MAM-exposed rats were sacrificed for histological staining. Results: At P15, the retrosplenial cortex (RSC) of rats with MCDs showed decreased neuronal nuclei, parvalbumin, and reelin expressions. Moreover, dendritic arborization of pyramidal cells in the RSC significantly decreased in infant rats with MCDs. In vivo MRI showed significantly decreased GluCEST (%) in the RSC of rats with MCDs (p = 0.000) and a significant correlation between GluCEST (%) and RSC thickness (r = 0.685, p = 0.003). The rats with MCDs showed reduced glutamate (p = 0.002), N-acetylaspartate (p = 0.002), and macromolecule and lipid levels (p = 0.027) and significantly reduced fractional anisotropy values in the RSC. Conclusion: In vivo MRI revealed reduced neuronal population and dendritic arborization in the RSC of infant rats with MCDs during the early postnatal period. These pathological changes of the cortex could serve as clinical imaging biomarkers of MCDs in infants.

Deletion of c16orf45 in zebrafish results in a low fertilization rate and increased thigmotaxis

c16orf45 is located at 16p13.11, an important locus related to neurodevelopmental diseases. Clinical studies have demonstrated that c16orf45 is associated with various neurodevelopmental diseases. To further elucidate the effect of c16orf45 on neural development, we constructed a zebrafish model with a stably inherited c16orf45 deletion via CRISPR/Cas9 technology. We found that deletion of c16orf45 significantly reduced the zebrafish fertilization rate, and both females and males showed reduced fertility. Meanwhile, the homozygous c16orf45 knockout zebrafish showed a developmental delay at 24 hr postfertilization (hpf). However, morphological changes were not apparent after 2 days postfertilization (dpf). Notably, the results of behavioral experiments revealed increased thigmotaxis in c16orf45^{- / -} zebrafish at 2 months. In conclusion, these findings demonstrate that c16orf45 plays an important role in nervous system and reproductive system.

Cortical formation abnormalities on foetal MR imaging: a proposed classification system trialled on 356 cases from Italian and UK centres

OBJECTIVE

To formulate a classification system for foetal cortical formation abnormalities (CFAs) based on in utero magnetic resonance (iuMR) appearances and trial it in 356 cases.

METHODS

This retrospective study included all cases of foetal CFA diagnosed between 2000 and 2017 from seven centres in Italy and UK. All of the studies were reviewed by a panel of paediatric neuroradiologists experienced in iuMR with the aid of an algorithm designed to categorise the abnormalities.

RESULTS

Consensus expert review confirmed 356 foetuses with CFA and the first level of classification distinguished bilateral CFA (229/356-64%) from unilateral CFA (127/356-36%) cases with sub-classification of the bilateral cases into asymmetric (65/356-18%) and symmetric (164/356-46%) involvement. There was a statistically significant excess of foetuses with small head size, e.g. 17% of the cohort had a bi-parietal diameter < 3rd centile. There was a small but statistically significant excess of males in the cohort. Further categorisation was made on fine anatomical structure.

CONCLUSIONS

It is often not possible to classify foetal CFA using the principles and nomenclature used in paediatric neuroradiology. We have created a classification system for foetal CFA based on the analysis of 356 cases and believe that this will assist future research designed to correlate ante-natal and post-natal imaging features and understand the clinical sequelae of CFA described in utero.

KEY POINTS

• We describe a morphological classification system of foetal brain cortical formation abnormalities that can be used in clinical practice. • This classification system can be used in future research studies to evaluate the long-term imaging and clinical outcomes of foetal brain cortical formation abnormalities in 17- to 38-week gestational age range. • The practical value of the work is in providing a framework and language to look for imaging clues that may differentiate between different CFA in further studies.

The yield of chromosomal microarray testing for cases of abnormal fetal head circumference

OBJECTIVES

Chromosomal microarray analysis (CMA) is the method of choice for genetic work-up in cases of fetal malformations. We assessed the detection rate of CMA in cases of abnormal fetal head circumference (HC).

METHODS

The study cohort was based on 81 cases of amniocenteses performed throughout Israel for the indication of microcephaly (53) or macrocephaly (28), from January 2015 through December 2018. We retrieved data regarding the clinical background, parental HCs and work-up during the pregnancy from genetic counseling summaries and from patients' medical records.

RESULTS

There was only one likely pathogenic CMA result (1.89%): a 400-kb microdeletion at 16p13.3 detected in a case of isolated microcephaly. No pathogenic results were found in the macrocephaly group. Most fetuses with microcephaly were female (87.8%), while the majority with macrocephaly were males (86.4%).

CONCLUSIONS

The results imply that CMA analysis in pregnancies with microcephaly may carry a small yield compared to other indications. Regarding macrocephaly, our cohort was too small to draw conclusions. In light of the significant gender effect on the diagnosis of abnormal HC, standardization of fetal HC charts according to fetal gender may normalize cases that were categorized outside the normal range and may increase the yield of CMA for cases of abnormal HC.

mTOR pathway activation in focal cortical dysplasia

BACKGROUND

Focal cortical dysplasia (FCD) is a localized cortical malformation and considerable morphological overlap exists between FCD IIB and neurological lesions associated with Tuberous sclerosis complex (TSC). Abnormal mTOR pathway secondary to somatic mTOR mutation and TSC gene mutation linked to PI3K/AKT/mTOR pathway have supported the hypothesis of common pathogenesis involved. Role of converging pathway, viz. Wnt/β-Catenin and mTOR is unknown in FCD. We aimed to analyse FCD IIB for TSC1/TSC2 mutations, immunoreactivity of hamartin, tuberin, mTOR and Wnt signalling cascades, and stem cell markers.

MATERIALS AND METHODS

Sixteen FCD IIB cases were retrieved along with 16 FCD IIA cases for comparison. Immunohistochemistry was performed for tuberin, hamartin, mTOR pathway markers, markers of stem cell phenotype, and Wnt pathway markers. Mutation analysis for TSC1 and TSC2 was performed by sequencing in 9 FCD cases.

RESULTS

All FCD cases showed preserved hamartin and tuberin immunoreactivity. Aberrant immunoreactivity of phospho-P70S6 kinase, S6 ribosomal, phospho-S6 ribosomal and Stat3 was noted in FCD IIB, with variable phospho-4E-BP1 (45%) and absent phospho-Stat3 expression. Immunoreactivity for phospho-P70S6 kinase (100%), S6 ribosomal protein (100%) and Stat3 (100%) was noted in FCD IIA, but not for phospho-S6 ribosomal, phospho-4E-BP1 and phospho-Stat3. c-Myc immunoreactivity was noted in all FCD cases. Nestin (81%) and Sox 2 (88%) stained balloon cells in FCD IIB (44%), while in FCD IIA cases were negative. All FCD cases were immunopositive for Wnt, but were negative for β-Catenin and cyclin-D1. TSC mutations were detected in two cases of FCD IIB.

CONCLUSION

Abnormal mTOR pathway activation exists in FCD IIB and IIA, however, shows differential immunoreactivity profile, indicating varying degrees of dysregulation. Labelling of neuronal stem cell markers in balloon cells suggests they are phenotypically immature. TSC1/2 mutation play role in the pathogenesis of FCD. Deep targeted sequencing is preferred diagnostic technique since conventional sanger sequencing often fails to detect low-allele frequency variants involved in mTOR/TSC pathway genes, commonly found in FCD.

De novo mutations of TUBB2A cause infantile-onset epilepsy and developmental delay

We analyzed our two new cases of infantile-onset epilepsy with developmental delay with de novo variant in TUBB2A and review the related literatures. Our two probands were both girls with infantile-onset epilepsy and global developmental delay. Case 1 had a novel de novo heterozygous missense variant: c.728C>T [p.Pro243Leu] (NM_001069.2). Her brain magnetic resonance imaging (MRI) showed nonspecific white matter myelination delay and slightly enlarged anterior horn of lateral ventricle. Her epilepsy had been controlled by TPM monotherapy. Case 2 had a reported de novo variant c.743C>T [p.Ala248Val] (NM_001069.2). Her brain MRI showed bilateral microgyria and corpus callosum dysplasia. A total of seven TUBB2A mutations cases had been published previously in five papers, therefore, until now, there were nine patients with TUBB2A mutations. All patients had developmental delay, among them seven cases also with infantile-onset epilepsy, one case with abnormal EEG but without clinical seizures. There are six cases that have different degree of cortical dysplasia, one case with cerebellar vermis atrophy and brainstem sacsinopathy, the rest two cases have no obvious brain structural abnormalities. There was one case with variant c.1249G>A (p.D417N) that had atypical clinical presentation, including prominent progressive spastic ataxia, sensory motor axonal neuropathy, and bilateral optic macular dystrophy, but relatively mild intellectual disability, his MRI showed cerebellar atrophy, thinning of the corpus callosum and pons sacsinopathy, but no cortical malformation. The p.A248V mutation was the most common mutation occurred in three patients (3/9). The clinical phenotypes of these three patients were similar, all of them had global developmental delay with no language and corpus callosum dysplasia, two cases with epilepsy and the other one only have EEG epileptic discharges without clinical seizure, two cases with cortical dysplasia and the other one without obvious brain malformation. In brief, global developmental delay was the most common phenotype of TUBB2A mutation-related disease, most cases also had infantile-onset epilepsy and cortical dysplasia and corpus callosum dysplasia. The region between seventh and eighth alpha-helix of TUBB2A may be a "hot spot" mutation domain.

The journey of Zika to the developing brain

Zika virus is a mosquito-borne Flavivirus originally isolated from humans in 1952. Following its re-emergence in Brazil in 2015, an increase in the number of babies born with microcephaly to infected mothers was observed. Microcephaly is a neurodevelopmental disorder, characterised phenotypically by a smaller than average head size, and is usually developed in utero. The 2015 outbreak in the Americas led to the World Health Organisation declaring Zika a Public Health Emergency of International Concern. Since then, much research into the effects of Zika has been carried out. Studies have investigated the structure of the virus, its effects on and evasion of the immune response, cellular entry including target receptors, its transmission from infected mother to foetus and its cellular targets. This review discusses current knowledge and novel research into these areas, in hope of developing a further understanding of how exposure of pregnant women to the Zika virus can lead to impaired brain development of their foetus. Although no longer considered an epidemic in the Americas, the mechanism by which Zika acts is still not comprehensively and wholly understood, and this understanding will be crucial in developing effective vaccines and treatments.

Early Chronic Carbamazepine-in-Food Administration to MAM/Pilocarpine Rats Does Not Affect Convulsive Motor Seizures

Antiepileptic drug-resistance is a major health problem in patients with cortical dysplasia (CD). Whether drug-resistant epilepsy is associated with progressive brain damage is still debated. We previously generated a rat model of acquired CD, the methylazoxymethanol-pilocarpine (MP) rat, in which the occurrence of status epilepticus and subsequent spontaneous seizures induce progressive brain damage (Nobili et al., 2015). The present study tested the outcome of early-chronic carbamazepine (CBZ) administration on both seizure activity and brain damage in MP rats. We took advantage of the non-invasive CBZ-in-food administration protocol, established by Ali (2012), which proved effective in suppressing generalized convulsive seizures in kainic acid rat model of epilepsy. MP rats were treated immediately after the onset of the first spontaneous seizure with 300 mg/kg/day CBZ formulated in pellets for a two-months-trial. CBZ-treated rats were continuously video-monitored to detect seizure activity and were compared with untreated epileptic MP rats. Despite CBZ serum levels in treated rats were within the suggested therapeutic range for humans, CBZ affected spontaneous convulsive seizures in 2 out of 10 treated rats (responders), whereas the remaining animals (non-responders) did not show any difference when compared to untreated MP rats. Histological analysis revealed cortical thinning paralleled by robust staining of Fluoro-Jade⁺ (FJ⁺) degenerating neurons and diffuse tissue necrosis in CBZ-non-responder vs CBZ-responder rats. Data reported here suggest that MP rat model represents suitable experimental setting where to investigate mechanisms of CD-related drug-resistant epilepsy and to verify if modulation of seizures, with appropriate treatment, may reduce seizure-induced brain damage.

Detecting focal cortical dysplasia lesions from FLAIR-negative images based on cortical thickness

Background

Focal cortical dysplasia (FCD) is a neuronal migration disorder and is a major cause of drug-resistant epilepsy. However, many focal abnormalities remain undetected during routine visual inspection, and many patients with histologically confirmed FCD have normal fluid-attenuated inversion recovery (FLAIR-negative) images. The aim of this study was to quantitatively evaluate the changes in cortical thickness with magnetic resonance (MR) imaging of patients to identify FCD lesions from FLAIR-negative images.

Methods

We first used the three-dimensional (3D) Laplace method to calculate the cortical thickness for individuals and obtained the cortical thickness mean image and cortical thickness standard deviation (SD) image based on all 32 healthy controls. Then, a cortical thickness extension map was computed by subtracting the cortical thickness mean image from the cortical thickness image of each patient and dividing the result by the cortical thickness SD image. Finally, clusters of voxels larger than three were defined as the FCD lesion area from the cortical thickness extension map.

Results

The results showed that three of the four lesions that occurred in non-temporal areas were detected in three patients, but the detection failed in three patients with lesions that occurred in the temporal area. The quantitative analysis of the detected lesions in voxel-wise on images revealed the following: specificity (99.78%), accuracy (99.76%), recall (67.45%), precision (20.42%), Dice coefficient (30.01%), Youden index (67.23%) and area under the curve (AUC) (83.62%).

Conclusion

Our studies demonstrate an effective method to localize lesions in non-temporal lobe regions. This novel method automatically detected FCD lesions using only FLAIR-negative images from patients and was based only on cortical thickness feature. The method is noninvasive and more effective than a visual analysis for helping doctors make a diagnosis.

Differential Expression Hallmarks of Interneurons in Different Types of Focal Cortical Dysplasia

Focal cortical dysplasia (FCD) is the main cause of medically intractable pediatric epilepsy. Previous studies have suggested that alteration of cortical interneurons and abnormal cytoarchitecture have been linked to initiation and development for seizure. However, whether each individual subpopulation of cortical interneurons is linked to distinct FCD subtypes remains largely unknown. Here, we retrospectively analyzed both control samples and epileptic specimens pathologically diagnosed with FCD types Ia, IIa, or IIb. We quantified three major interneuron (IN) subpopulations, including parvalbumin (PV)-, somatostatin (Sst)-, and vasoactive intestinal peptide (Vip)-positive INs across all the subgroups. Additionally, we calculated the ratio of the subpopulations of INs to the major INs (mINs) by defining the total number of the PV-, Sst-, and Vip-INs as mINs. Compared with the control, the density of the PV-INs in FCD type IIb was significantly lower, and the ratio of PV/mINs was lower in the superficial part of the cortex of the FCD type Ia and IIb groups. Interestingly, we found a significant increase in the ratio of Vip/mINs only in FCD type IIb. Overall, these results suggest that in addition to a reduction in PV-INs, the increase in Vip/mINs may be related to the initiation of epilepsy in FCD type IIb. Furthermore, the increase in Vip/mINs in FCD type IIb may, from the IN development perspective, indicate that FCD type IIb forms during earlier stages of pregnancy than FCD type Ia.

Recurrent NEDD4L Variant in Periventricular Nodular Heterotopia, Polymicrogyria and Syndactyly

NEDD4L encodes an ubiquitin ligase which is expressed in the cortex and ventricular zone of the fetal brain. Missense variants in NEDD4L have been reported in nine patients with periventricular nodular heterotopia (PNH), polymicrogyria, cleft palate, and syndactyly. All reported variants are located in the HECT domain, causing deregulation of signaling pathways, including the AKT/mTOR pathway. Here we describe a first familial case with four affected members with a high degree of intra-familial phenotypic variability. Phenotypic features in the proband consisted of severe neurodevelopmental delay, refractory seizures, bilateral PNH, and perisylvian polymicrogyria. The other family members were less severely affected with mild developmental delay and isolated bilateral PNH. All family members had syndactyly. An unrelated patient presented with severe neurodevelopmental delay, seizures, and hypospadias, expanding the phenotypic spectrum. MRI revealed bilateral PNH and perisylvian polymicrogyria. All tested patients carry the recurrent variant c.623G > A, p.(Arg208Gln) in the WW domain of NEDD4L. The variant in the unrelated patient occurred de novo. This is the first report of a NEDD4L variant located in the WW domain which is probably involved in the recognition of substrates for ligation suggesting a loss of function variant.

Endoplasmic reticulum transmembrane protein TMTC3 contributes to O-mannosylation of E-cadherin, cellular adherence, and embryonic gastrulation

Protein glycosylation plays essential roles in protein structure, stability, and activity such as cell adhesion. The cadherin superfamily of adhesion molecules carry O-linked mannose glycans at conserved sites and it was recently demonstrated that the transmembrane and tetratricopeptide repeat-containing proteins 1-4 (TMTC1-4) gene products contribute to the addition of these O-linked mannoses. Here, biochemical, cell biological, and organismal analysis was used to determine that TMTC3 supports the O-mannosylation of E-cadherin, cellular adhesion, and embryonic gastrulation. Using genetically engineered cells lacking all four TMTC genes, overexpression of TMTC3 rescued O-linked glycosylation of E-cadherin and cell adherence. The knockdown of the Tmtcs in Xenopus laevis embryos caused a delay in gastrulation that was rescued by the addition of human TMTC3. Mutations in TMTC3 have been linked to neuronal cell migration diseases including Cobblestone lissencephaly. Analysis of TMTC3 mutations associated with Cobblestone lissencephaly found that three of the variants exhibit reduced stability and missence mutations were unable to complement TMTC3 rescue of gastrulation in Xenopus embryo development. Our study demonstrates that TMTC3 regulates O-linked glycosylation and cadherin-mediated adherence, providing insight into its effect on cellular adherence and migration, as well the basis of TMTC3-associated Cobblestone lissencephaly.

Clinical Implementation of Targeted Gene Sequencing for Malformation of Cortical Development

BACKGROUND

Malformations of cortical development comprise phenotypically heterogeneous conditions, and the diagnostic value of genetic testing in blood still remains to be elucidated. We used targeted gene sequencing to identify malformations of cortical development caused by germline mutations and characteristics associated with pathogenic mutations.

METHODS

A total of 81 patients with malformations of cortical development were included. Genomic DNA was isolated from peripheral blood. Ninety-six genes were assessed using a targeted next-generation sequencing panel. Single-nucleotide variants and exonic and chromosomal copy number variations were examined with our customized pipeline.

RESULTS

Genetic causes were identified from blood in 19 (23.5%) patients with malformations of cortical development; 14 patients had pathogenic or likely pathogenic single-nucleotide variants in seven genes, including DCX (n = 5), DEPDC5 (n = 2), PAFAH1B1 (n = 3), TUBA1A (n = 1), TUBA8 (n = 1), TUBB2B (n = 1), and TUBB3 (n = 1). Five patients had pathogenic copy number variations. Multifocal involvement of the lesion (tangential distribution, P < 0.001) and concurrent involvement of multiple structures such as the cortex, white matter, and ventricle (radial distribution, P = 0.003) were more commonly found in patients with identified genetic causes. Intellectual disability was also more commonly associated with pathogenic mutations (P = 0.048). In a multivariable regression analysis, both tangential and radial radiological distribution of malformations of cortical development were independently associated with positive germline test results.

CONCLUSION

We identified germline mutations in almost one-fourth of our patients with malformations of cortical development by using targeted gene sequencing. Germline abnormalities were more likely found in patients who had multifocal malformations of cortical development.

Advances in genetic testing and optimization of clinical management in children and adults with epilepsy

Introduction: Epileptic disorders are a heterogeneous group of medical conditions with epilepsy as the common denominator. Genetic causes, electro-clinical features, and management significantly vary according to the specific condition.Areas covered: Relevant diagnostic advances have been achieved thanks to the advent of Next Generation Sequencing (NGS)-based molecular techniques. These revolutionary tools allow to sequence all coding (whole exome sequencing, WES) and non-coding (whole genome sequencing, WGS) regions of human genome, with a potentially huge impact on patient care and scientific research.Expert opinion: The application of these tests in children and adults with epilepsy has led to the identification of new causative genes, widening the knowledge on the pathophysiology of epilepsy and resulting in therapeutic implications. This review will explore the most recent advancements in genetic testing and provide up-to-date approaches for the choice of the correct test in patients with epilepsy.

Cortical Malformations: Lessons in Human Brain Development

Creating a functional cerebral cortex requires a series of complex and well-coordinated developmental steps. These steps have evolved across species with the emergence of cortical gyrification and coincided with more complex behaviors. The presence of diverse progenitor cells, a protracted timeline for neuronal migration and maturation, and diverse neuronal types are developmental features that have emerged in the gyrated cortex. These factors could explain how the human brain has expanded in size and complexity. However, their complex nature also renders new avenues of vulnerability by providing additional cell types that could contribute to disease and longer time windows that could impact the composition and organization of the cortical circuit. We aim to discuss the unique developmental steps observed in human corticogenesis and propose how disruption of these species-unique processes could lead to malformations of cortical development.

Inborn errors of metabolism leading to neuronal migration defects

The development and organisation of the human brain start in the embryonic stage and is a highly complex orchestrated process. It depends on series of cellular mechanisms that are precisely regulated by multiple proteins, signalling pathways and non-protein-coding genes. A crucial process during cerebral cortex development is the migration of nascent neuronal cells to their appropriate positions and their associated differentiation into layer-specific neurons. Neuronal migration defects (NMD) comprise a heterogeneous group of neurodevelopmental disorders including monogenetic disorders and residual syndromes due to damaging factors during prenatal development like infections, maternal diabetes mellitus or phenylketonuria, trauma, and drug use. Multifactorial causes are also possible. Classification into lissencephaly, polymicrogyria, schizencephaly, and neuronal heterotopia is based on the visible morphologic cortex anomalies. Characteristic clinical features of NMDs are severe psychomotor developmental delay, severe intellectual disability, intractable epilepsy, and dysmorphisms. Neurometabolic disorders only form a small subgroup within the large group of NMDs. The prototypes are peroxisomal biogenesis disorders, peroxisomal ß-oxidation defects and congenital disorders of O-glycosylation. The rapid evolution of biotechnology has resulted in an ongoing identification of metabolic and non-metabolic disease genes for NMDs. Nevertheless, we are far away from understanding the specific role of cortical genes and metabolites on spatial and temporal regulation of human cortex development and associated malformations. This limited understanding of the pathogenesis hinders the attempt for therapeutic approaches. In this article, we provide an overview of the most important cortical malformations and potential underlying neurometabolic disorders.

Optimized stereoelectroencephalography-guided radiofrequency thermocoagulation in the treatment of patients with focal epilepsy

Epilepsy is a severe health disorder affecting people of all ages with high prevalence worldwide. The introduction of new antiepileptic drugs has yielded notable effects in recent decades, yet there are still approximately 30% of patients with seizures refractory to medical therapy. Open surgical resection is widely accepted as a highly effective approach for the treatment of drug-resistant focal epilepsy if the epileptogenic zone can be precisely delineated. However, concerns about the impact of open surgery on brain function have driven considerable interest in less invasive techniques. Clinically, stereoelectroencephalography (SEEG) offers a unique means of exploring the pathophysiologic process and accurately mapping the epileptogenic network in presurgical evaluations for patients with epilepsy because of insufficient information from other noninvasive investigations. Moreover, SEEG-guided radiofrequency thermocoagulation (SEEG-guided RF-TC), which ablates lesions directly through the recording electrodes according to electroclinical evidence, has emerged as a promising, minimally invasive modality with notable preservation of neurocognitive functions. This critical review summarizes the technical details of the parameters and the selection of patients for SEEG-guided RF-TC based on the literature as well as our experiences. With respect to the parameters, the power and duration of RF-TC are discussed. In particular, an optimized SEEG-guided RF-TC modality that integrates more contacts from multiple different electrodes to create a confluent lesioning field is proposed for a more curative effect in comparison to the current protocol of palliative treatment in which RF-TC selectively disrupts critical hubs in the epileptic network through contiguous contacts within the range of a single electrode. Currently, SEEG-guided RF-TC is indicated for a variety of small, deeply seeded and well-demarcated epileptogenic foci, such as deep heterotopic nodules and hypothalamic hamartoma. The efficacy of treating patients with focal cortical dysplasias in the eloquent cortex and with mesial temporal lobe epilepsy associated with hippocampal sclerosis needs to be further determined. Given the small number of patients reported, randomized controlled trials are necessary to compare the efficacy of SEEG-guided RF-TC with conventional methods in the future.

Language Dominance in Patients With Malformations of Cortical Development and Epilepsy

Background: Language function may be reorganized in patients with malformations of cortical development (MCD). This prospective cohort study aimed in assessing language dominance in a large group of patients with MCD and epilepsy using functional MRI (fMRI).

Methods: Sixty-eight patients (40 women) aged 10–73 years (median, 28.0; interquartile range, 19) with MCD and epilepsy underwent 1.5 T MRI and fMRI (word generation task). Single-subject image analysis was performed with statistical parametric mapping (SPM12). Language lateralization indices (LIs) were defined for statistically significantly activated voxels in Broca's and Wernicke's areas using the formula: LI = (V_L – V_R)/(V_L + V_R) × 100, where V_L and V_R were sets of activated voxels on the left and on the right, respectively. Language laterality was considered typical if LI was between +20 and +100 or atypical if LI was between +19 and −100.

Results: fMRI signal was elicited in 55 of 68 (81%) patients. In 18 of 55 (33%) patients, language dominance was typical, and in 37 of 55 (67%) patients, atypical (in 68%, right hemispheric; in 32%, bilateral). Language dominance was not influenced by handedness, electroclinical, and imaging features.

Conclusions: In this prospective study on a large group of patients with MCD and epilepsy, about two-thirds had atypical language dominance. These results may contribute to assessing risks of postsurgical language deficits and could assist in planning of “cortical mapping” with intracranial electrodes in patients who undergo presurgical assessment.

Heterogeneous clinical phenotypes and cerebral malformations reflected by rotatin cellular dynamics

Recessive mutations in RTTN, encoding the protein rotatin, were originally identified as cause of polymicrogyria, a cortical malformation. With time, a wide variety of other brain malformations has been ascribed to RTTN mutations, including primary microcephaly. Rotatin is a centrosomal protein possibly involved in centriolar elongation and ciliogenesis. However, the function of rotatin in brain development is largely unknown and the molecular disease mechanism underlying cortical malformations has not yet been elucidated. We performed both clinical and cell biological studies, aimed at clarifying rotatin function and pathogenesis. Review of the 23 published and five unpublished clinical cases and genomic mutations, including the effect of novel deep intronic pathogenic mutations on RTTN transcripts, allowed us to extrapolate the core phenotype, consisting of intellectual disability, short stature, microcephaly, lissencephaly, periventricular heterotopia, polymicrogyria and other malformations. We show that the severity of the phenotype is related to residual function of the protein, not only the level of mRNA expression. Skin fibroblasts from eight affected individuals were studied by high resolution immunomicroscopy and flow cytometry, in parallel with in vitro expression of RTTN in HEK293T cells. We demonstrate that rotatin regulates different phases of the cell cycle and is mislocalized in affected individuals. Mutant cells showed consistent and severe mitotic failure with centrosome amplification and multipolar spindle formation, leading to aneuploidy and apoptosis, which could relate to depletion of neuronal progenitors often observed in microcephaly. We confirmed the role of rotatin in functional and structural maintenance of primary cilia and determined that the protein localized not only to the basal body, but also to the axoneme, proving the functional interconnectivity between ciliogenesis and cell cycle progression. Proteomics analysis of both native and exogenous rotatin uncovered that rotatin interacts with the neuronal (non-muscle) myosin heavy chain subunits, motors of nucleokinesis during neuronal migration, and in human induced pluripotent stem cell-derived bipolar mature neurons rotatin localizes at the centrosome in the leading edge. This illustrates the role of rotatin in neuronal migration. These different functions of rotatin explain why RTTN mutations can lead to heterogeneous cerebral malformations, both related to proliferation and migration defects.

A Model of Brain Folding Based on Strong Local and Weak Long-Range Connectivity Requirements

Throughout the animal kingdom, the structure of the central nervous system varies widely from distributed ganglia in worms to compact brains with varying degrees of folding in mammals. The differences in structure may indicate a fundamentally different circuit organization. However, the folded brain most likely is a direct result of mechanical forces when considering that a larger surface area of cortex packs into the restricted volume provided by the skull. Here, we introduce a computational model that instead of modeling mechanical forces relies on dimension reduction methods to place neurons according to specific connectivity requirements. For a simplified connectivity with strong local and weak long-range connections, our model predicts a transition from separate ganglia through smooth brain structures to heavily folded brains as the number of cortical columns increases. The model reproduces experimentally determined relationships between metrics of cortical folding and its pathological phenotypes in lissencephaly, polymicrogyria, microcephaly, autism, and schizophrenia. This suggests that mechanical forces that are known to lead to cortical folding may synergistically contribute to arrangements that reduce wiring. Our model provides a unified conceptual understanding of gyrification linking cellular connectivity and macroscopic structures in large-scale neural network models of the brain.

TMX2 Is a Crucial Regulator of Cellular Redox State, and Its Dysfunction Causes Severe Brain Developmental Abnormalities

The redox state of the neural progenitors regulates physiological processes such as neuronal differentiation and dendritic and axonal growth. The relevance of endoplasmic reticulum (ER)-associated oxidoreductases in these processes is largely unexplored. We describe a severe neurological disorder caused by bi-allelic loss-of-function variants in thioredoxin (TRX)-related transmembrane-2 (TMX2); these variants were detected by exome sequencing in 14 affected individuals from ten unrelated families presenting with congenital microcephaly, cortical polymicrogyria, and other migration disorders. TMX2 encodes one of the five TMX proteins of the protein disulfide isomerase family, hitherto not linked to human developmental brain disease. Our mechanistic studies on protein function show that TMX2 localizes to the ER mitochondria-associated membranes (MAMs), is involved in posttranslational modification and protein folding, and undergoes physical interaction with the MAM-associated and ER folding chaperone calnexin and ER calcium pump SERCA2. These interactions are functionally relevant because TMX2-deficient fibroblasts show decreased mitochondrial respiratory reserve capacity and compensatory increased glycolytic activity. Intriguingly, under basal conditions TMX2 occurs in both reduced and oxidized monomeric form, while it forms a stable dimer under treatment with hydrogen peroxide, recently recognized as a signaling molecule in neural morphogenesis and axonal pathfinding. Exogenous expression of the pathogenic TMX2 variants or of variants with an in vitro mutagenized TRX domain induces a constitutive TMX2 polymerization, mimicking an increased oxidative state. Altogether these data uncover TMX2 as a sensor in the MAM-regulated redox signaling pathway and identify it as a key adaptive regulator of neuronal proliferation, migration, and organization in the developing brain.

Regularized siamese neural network for unsupervised outlier detection on brain multiparametric magnetic resonance imaging: Application to epilepsy lesion screening

In this study, we propose a novel anomaly detection model targeting subtle brain lesions in multiparametric MRI. To compensate for the lack of annotated data adequately sampling the heterogeneity of such pathologies, we cast this problem as an outlier detection problem and introduce a novel configuration of unsupervised deep siamese networks to learn normal brain representations using a series of non-pathological brain scans. The proposed siamese network, composed of stacked convolutional autoencoders as subnetworks is designed to map patches extracted from healthy control scans only and centered at the same spatial localization to 'close' representations with respect to the chosen metric in a latent space. It is based on a novel loss function combining a similarity term and a regularization term compensating for the lack of dissimilar pairs. These latent representations are then fed into oc-SVM models at voxel-level to produce anomaly score maps. We evaluate the performance of our brain anomaly detection model to detect subtle epilepsy lesions in multiparametric (T1-weighted, FLAIR) MRI exams considered as normal (MRI-negative). Our detection model trained on 75 healthy subjects and validated on 21 epilepsy patients (with 18 MRI-negatives) achieves a maximum sensitivity of 61% on the MRI-negative lesions, identified among the 5 most suspicious detections on average. It is shown to outperform detection models based on the same architecture but with stacked convolutional or Wasserstein autoencoders as unsupervised feature extraction mechanisms.

Ultra-High-Field Targeted Imaging of Focal Cortical Dysplasia: The Intracortical Black Line Sign in Type IIb

BACKGROUND AND PURPOSE

Conventional MR imaging has limitations in detecting focal cortical dysplasia. We assessed the added value of 7T in patients with histologically proved focal cortical dysplasia to highlight correlations between neuropathology and ultra-high-field imaging.

MATERIALS AND METHODS

Between 2013 and 2019, we performed a standardized 7T MR imaging protocol in patients with drug-resistant focal epilepsy. We focused on 12 patients in whom postsurgical histopathology revealed focal cortical dysplasia and explored the diagnostic yield of preoperative 7T versus 1.5/3T MR imaging and the correlations of imaging findings with histopathology. We also assessed the relationship between epilepsy surgery outcome and the completeness of surgical removal of the MR imaging-visible structural abnormality.

RESULTS

We observed clear abnormalities in 10/12 patients using 7T versus 9/12 revealed by 1.5/3T MR imaging. In patients with focal cortical dysplasia I, 7T MR imaging did not disclose morphologic abnormalities (n = 0/2). In patients with focal cortical dysplasia II, 7T uncovered morphologic signs that were not visible on clinical imaging in 1 patient with focal cortical dysplasia IIa (n = 1/4) and in all those with focal cortical dysplasia IIb (n = 6/6). T2*WI provided the highest added value, disclosing a peculiar intracortical hypointense band (black line) in 5/6 patients with focal cortical dysplasia IIb. The complete removal of the black line was associated with good postsurgical outcome (n = 4/5), while its incomplete removal yielded unsatisfactory results (n = 1/5).

CONCLUSIONS

The high sensitivity of 7T T2*-weighted images provides an additional tool in defining potential morphologic markers of high epileptogenicity within the dysplastic tissue of focal cortical dysplasia IIb and will likely help to more precisely plan epilepsy surgery and explain surgical failures.

Disorganized Patterns of Sulcal Position in Fetal Brains with Agenesis of Corpus Callosum

Fetuses with isolated agenesis of the corpus callosum (ACC) are associated with a broad spectrum of neurodevelopmental disability that cannot be specifically predicted in prenatal neuroimaging. We hypothesized that ACC may be associated with aberrant cortical folding. In this study, we determined altered patterning of early primary sulci development in fetuses with isolated ACC using novel quantitative sulcal pattern analysis which measures deviations of regional sulcal features (position, depth, and area) and their intersulcal relationships in 7 fetuses with isolated ACC (27.1 ± 3.8 weeks of gestation, mean ± SD) and 17 typically developing (TD) fetuses (25.7 ± 2.0 weeks) from normal templates. Fetuses with ACC showed significant alterations in absolute sulcal positions and relative intersulcal positional relationship compared to TD fetuses, which were not detected by traditional gyrification index. Our results reveal altered sulcal positional development even in isolated ACC that is present as early as the second trimester and continues throughout the fetal period. It might originate from altered white matter connections and portend functional variances in later life.