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

Comparative Analysis Between Flaviviruses Reveals Specific Neural Stem Cell Tropism for Zika Virus in the Mouse Developing Neocortex

The recent Zika outbreak in South America and French Polynesia was associated with an epidemic of microcephaly, a disease characterized by a reduced size of the cerebral cortex. Other members of the Flavivirus genus, including West Nile virus (WNV), can cause encephalitis but were not demonstrated to cause microcephaly. It remains unclear whether Zika virus (ZIKV) and other flaviviruses may infect different cell populations in the developing neocortex and lead to distinct developmental defects. Here, we describe an assay to infect mouse E15 embryonic brain slices with ZIKV, WNV and dengue virus serotype 4 (DENV-4). We show that this tissue is able to support viral replication of ZIKV and WNV, but not DENV-4. Cell fate analysis reveals a remarkable tropism of ZIKV infection for neural stem cells. Closely related WNV displays a very different tropism of infection, with a bias towards neurons. We further show that ZIKV infection, but not WNV infection, impairs cell cycle progression of neural stem cells. Both viruses inhibited apoptosis at early stages of infection. This work establishes a powerful comparative approach to identify ZIKV-specific alterations in the developing neocortex and reveals specific preferential infection of neural stem cells by ZIKV.

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Mouse embryonic brain slices sustain Zika and West Nile, but not Dengue-4, virus replication.

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Zika virus, but not West Nile virus, exhibits a selective tropism of infection for neural stem cells.

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Zika virus, but not West Nile virus, alters cell cycle progression of neural stem cells.

A Zika virus outbreak in South America is currently responsible for a large burst of microcephaly cases, a congenital brain malformation characterized by a reduced brain size. We describe here an assay to infect cultured mouse embryonic brain slices with Zika virus as well as other closely related flaviviruses not demonstrated to cause microcephaly. We show that Zika virus displays a specific pattern of infection in the developing brain, almost exclusively infecting neural stem cells. Zika virus impairs neural stem cell proliferation, an effect not seen for other flaviviruses and that may participate in the induction of microcephaly.

De Novo Mutations in DENR Disrupt Neuronal Development and Link Congenital Neurological Disorders to Faulty mRNA Translation Re-initiation

Disruptions to neuronal mRNA translation are hypothesized to underlie human neurodevelopmental syndromes. Notably, the mRNA translation re-initiation factor DENR is a regulator of eukaryotic translation and cell growth, but its mammalian functions are unknown. Here, we report that Denr influences the migration of murine cerebral cortical neurons in vivo with its binding partner Mcts1, whereas perturbations to Denr impair the long-term positioning, dendritic arborization, and dendritic spine characteristics of postnatal projection neurons. We characterized de novo missense mutations in DENR (p.C37Y and p.P121L) detected in two unrelated human subjects diagnosed with brain developmental disorder to find that each variant impairs the function of DENR in mRNA translation re-initiation and disrupts the migration and terminal branching of cortical neurons in different ways. Thus, our findings link human brain disorders to impaired mRNA translation re-initiation through perturbations in DENR (OMIM: 604550) function in neurons.

A restricted period for formation of outer subventricular zone defined by Cdh1 and Trnp1 levels

The outer subventricular zone (OSVZ) is a germinal layer playing key roles in the development of the neocortex, with particular relevance in gyrencephalic species such as human and ferret, where it contains abundant basal radial glia cells (bRGCs) that promote cortical expansion. Here we identify a brief period in ferret embryonic development when apical RGCs generate a burst of bRGCs that become founders of the OSVZ. After this period, bRGCs in the OSVZ proliferate and self-renew exclusively locally, thereby forming a self-sustained lineage independent from the other germinal layers. The time window for the brief period of OSVZ bRGC production is delineated by the coincident downregulation of Cdh1 and Trnp1, and their upregulation reduces bRGC production and prevents OSVZ seeding. This mechanism in cortical development may have key relevance in brain evolution and disease.

The outer subventricular zone (OSVZ) contains basal radial glial cells (bRGC) involved in cortical expansion in gyrencephalic mammals. Here the authors identify a developmental time window with marked production of bRGCs required to found the OSVZ that is dependent on coincident downregulation of Cdh1 and Trnp1.

Alterations in regional shape on ipsilateral and contralateral cortex contrast in children with unilateral cerebral palsy and are predictive of multiple outcomes

Congenital brain lesions result in a wide range of cerebral tissue alterations observed in children with cerebral palsy (CP) that are associated with a range of functional impairments. The relationship between injury severity and functional outcomes, however, remains poorly understood. This research investigates the differences in cortical shape between children with congenital brain lesions and typically developing children (TDC) and investigates the correlations between cortical shape and functional outcome in a large cohort of patients diagnosed with unilateral CP. Using 139 structural magnetic resonance images, including 95 patients with clinically diagnosed CP and 44 TDC, cortical segmentations were obtained using a modified expectation maximization algorithm. Three shape characteristics (cortical thickness, curvature, and sulcal depth) were computed within a number of cortical regions. Significant differences in these shape measures compared to the TDC were observed on both the injured hemisphere of children with CP (P < 0.004), as well as on the apparently uninjured hemisphere, illustrating potential compensatory mechanisms in these children. Furthermore, these shape measures were significantly correlated with several functional outcomes, including motor, cognition, vision, and communication (P < 0.012), with three out of these four models performing well on test set validation. This study highlights that cortical neuroplastic effects may be quantified using MR imaging, allowing morphological changes to be studied longitudinally, including any influence of treatment. Ultimately, such approaches could be used for the long term prediction of outcomes and the tailoring of treatment to individuals. Hum Brain Mapp 37:3588-3603, 2016. © 2016 Wiley Periodicals, Inc.

"Reverse Tigroid" Pattern in Pachygyria: A Novel Finding

Pachygyria is considered a subtype of lissencephaly which, in turn, is a spectrum of disorders caused by abnormal neuronal migration. Clinical presentation in this disorder may be varied including microcephaly, developmental delay, facial dysmorphism, seizures, and mental retardation. Magnetic resonance imaging (MRI) of brain identifies the exact nature and extent of the disease and helps in delineating further plan of management. A Tigroid pattern on axial MRI scan and leopard pattern on a sagittal plane has been classically reported in disorders of myelin formation such as metachromatic leukodystrophy and Pelizaeus–Merzbacher disease. We present here a case of pachygyria who presented to us with some atypical features including “tigroid-like stripes” and “leopard-like pattern” on MRI brain which has not been reported in the medical literature previously.

Cerebral cortex expansion and folding: what have we learned?

One of the most prominent features of the human brain is the fabulous size of the cerebral cortex and its intricate folding. Cortical folding takes place during embryonic development and is important to optimize the functional organization and wiring of the brain, as well as to allow fitting a large cortex in a limited cranial volume. Pathological alterations in size or folding of the human cortex lead to severe intellectual disability and intractable epilepsy. Hence, cortical expansion and folding are viewed as key processes in mammalian brain development and evolution, ultimately leading to increased intellectual performance and, eventually, to the emergence of human cognition. Here, we provide an overview and discuss some of the most significant advances in our understanding of cortical expansion and folding over the last decades. These include discoveries in multiple and diverse disciplines, from cellular and molecular mechanisms regulating cortical development and neurogenesis, genetic mechanisms defining the patterns of cortical folds, the biomechanics of cortical growth and buckling, lessons from human disease, and how genetic evolution steered cortical size and folding during mammalian evolution.

Expression Analysis Highlights AXL as a Candidate Zika Virus Entry Receptor in Neural Stem Cells

The recent outbreak of Zika virus (ZIKV) in Brazil has been linked to substantial increases in fetal abnormalities and microcephaly. However, information about the underlying molecular and cellular mechanisms connecting viral infection to these defects remains limited. In this study we have examined the expression of receptors implicated in cell entry of several enveloped viruses including ZIKV across diverse cell types in the developing brain. Using single-cell RNA-seq and immunohistochemistry, we found that the candidate viral entry receptor AXL is highly expressed by human radial glial cells, astrocytes, endothelial cells, and microglia in developing human cortex and by progenitor cells in developing retina. We also show that AXL expression in radial glia is conserved in developing mouse and ferret cortex and in human stem cell-derived cerebral organoids, highlighting multiple experimental systems that could be applied to study mechanisms of ZIKV infectivity and effects on brain development.

Prediction of microcephaly at birth using three reference ranges for fetal head circumference: can we improve prenatal diagnosis?

OBJECTIVE

To evaluate the prediction of microcephaly at birth (micB) using established and two new reference ranges for fetal head circumference (HC) and to assess whether integrating additional parameters can improve prediction.

METHODS

Microcephaly in utero was defined as a fetal HC 3SD below the mean for gestational age according to Jeanty et al.'s reference range. The records of cases with fetal microcephaly (Fmic) were evaluated for medical history, imaging findings, biometry and postnatal examination/autopsy findings. Microcephaly was confirmed at birth (micB) by an occipitofrontal circumference (OFC) or a brain weight at autopsy 2SD below the mean for gestational age. The new INTERGROWTH-21(st) Project and a recent Israeli reference for fetal growth were applied for evaluation of the Fmic positive predictive value (PPV) for diagnosis of micB cases. Optimal HC cut-offs were determined for each of the new references with the aim of detecting all micB cases whilst minimizing the number of false positives found to have a normal HC at birth. We also assessed the difference between the Z-scores of the prenatal HC and the corresponding OFC at birth, the frequency of small-for-gestational age (SGA), decreased HC/abdominal circumference (AC) and HC/femur length (FL) ratios, the prevalence of associated malformations and family history.

RESULTS

Forty-two fetuses were diagnosed as having Fmic according to the Jeanty reference, but micB was confirmed in only 24 (PPV, 57.1%). The optimal INTERGROWTH and Israeli reference HC cut-offs for micB diagnosis were mean - 3SD and mean - 2.3SD, resulting in a statistically non-significant improvement in PPV to 61.5% and 66.7%, respectively. The presence of a family history of microcephaly, SGA, associated malformations and application of stricter HC cut-offs resulted in a higher PPV of micB, although not statistically significant and with a concurrent increase in the number of false-negative results. The deviation of the HC from the mean, by all references, was significantly larger compared with the actual deviation of the OFC at birth, with mean differences between the corresponding Z-scores of -1.15, -1.95 and -0.74 for the Jeanty, INTERGROWTH and Israeli references, respectively.

CONCLUSIONS

The evaluated reference ranges all result in considerable over-diagnosis of fetal microcephaly. The use of the two new HC reference ranges did not significantly improve micB prediction compared with that of Jeanty et al., whilst use of additional characteristics and stricter HC cut-offs could improve the PPV with an increase in false negatives. The postnatal OFC deviates significantly less from the mean compared with the prenatal HC, and we propose that adjustment for this would enable better prediction of the actual OFC deviation at birth. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Copy number variations in children with brain malformations and refractory epilepsy

Brain malformations are a major cause of therapy-refractory epilepsy as well as neurological and developmental disabilities in children. This study examined the frequency and the nature of copy number variations among children with structural brain malformations and refractory epilepsy. The medical records of all children born between 1990 and 2009 in the epilepsy registry at the Astrid Lindgren's Children's Hospital were reviewed and 86 patients with refractory epilepsy and various brain malformations were identified. Array-CGH analysis was performed in 76 of the patients. Pathogenic copy number variations were detected in seven children (9.2%). In addition, rearrangements of unclear significance, but possibly pathogenic, were detected in 11 (14.5%) individuals. In 37 (48.7%) patients likely benign, but previously unreported, copy number variants were detected. Thus, a large proportion of our patients had at least one rare copy number variant. Our results suggest that array-CGH should be considered as a first line genetic test for children with cerebral malformations and refractory epilepsy unless there is a strong evidence for a specific monogenic syndrome.

Genes with high penetrance for syndromic and non-syndromic autism typically function within the nucleus and regulate gene expression

BACKGROUND

Intellectual disability (ID), autism, and epilepsy share frequent yet variable comorbidities with one another. In order to better understand potential genetic divergence underlying this variable risk, we studied genes responsible for monogenic IDs, grouped according to their autism and epilepsy comorbidities.

METHODS

Utilizing 465 different forms of ID with known molecular origins, we accessed available genetic databases in conjunction with gene ontology (GO) to determine whether the genetics underlying ID diverge according to its comorbidities with autism and epilepsy and if genes highly penetrant for autism or epilepsy share distinctive features that set them apart from genes that confer comparatively variable or no apparent risk.

RESULTS

The genetics of ID with autism are relatively enriched in terms associated with nervous system-specific processes and structural morphogenesis. In contrast, we find that ID with highly comorbid epilepsy (HCE) is modestly associated with lipid metabolic processes while ID without autism or epilepsy comorbidity (ID only) is enriched at the Golgi membrane. Highly comorbid autism (HCA) genes, on the other hand, are strongly enriched within the nucleus, are typically involved in regulation of gene expression, and, along with IDs with more variable autism, share strong ties with a core protein-protein interaction (PPI) network integral to basic patterning of the CNS.

CONCLUSIONS

According to GO terminology, autism-related gene products are integral to neural development. While it is difficult to draw firm conclusions regarding IDs unassociated with autism, it is clear that the majority of HCA genes are tightly linked with general dysregulation of gene expression, suggesting that disturbances to the chronology of neural maturation and patterning may be key in conferring susceptibility to autism spectrum conditions.

Important Roles of Ring Finger Protein 112 in Embryonic Vascular Development and Brain Functions

Rnf112 is a member of the RING finger protein family. The expression of Rnf112 is abundant in the brain and is regulated during brain development. Our previous study has revealed that Rnf112 can promote neuronal differentiation by inhibiting the progression of the cell cycle in cell models. In this study, we further revealed the important functions of Rnf112 in embryo development and in adult brain. Our data showed that most of the Rnf112 ^-/- embryos exhibited blood vascular defects and died in utero. Upon further investigation, we found that the survival rate of homozygous Rnf112 knockout mice in 129/sv and C57BL/6 mixed genetic background was increased. The survived newborns of Rnf112 ^-/- mice manifested growth retardation as indicated by smaller size and a reduced weight. Although the overall organization of the brain did not appear to be severely affected in Rnf112 ^-/- mice, using in vivo 3D MRI imaging, we found that when compared to wild-type littermates, brains of Rnf112 ^-/- mice were smaller. In addition, Rnf112 ^-/- mice displayed impairment of brain functions including motor balance, and spatial learning and memory. Our results provide important aspects for the study of Rnf112 gene functions.

Computational analysis in epilepsy neuroimaging: A survey of features and methods

Epilepsy affects 65 million people worldwide, a third of whom have seizures that are resistant to anti-epileptic medications. Some of these patients may be amenable to surgical therapy or treatment with implantable devices, but this usually requires delineation of discrete structural or functional lesion(s), which is challenging in a large percentage of these patients.

Advances in neuroimaging and machine learning allow semi-automated detection of malformations of cortical development (MCDs), a common cause of drug resistant epilepsy. A frequently asked question in the field is what techniques currently exist to assist radiologists in identifying these lesions, especially subtle forms of MCDs such as focal cortical dysplasia (FCD) Type I and low grade glial tumors. Below we introduce some of the common lesions encountered in patients with epilepsy and the common imaging findings that radiologists look for in these patients. We then review and discuss the computational techniques introduced over the past 10 years for quantifying and automatically detecting these imaging findings. Due to large variations in the accuracy and implementation of these studies, specific techniques are traditionally used at individual centers, often guided by local expertise, as well as selection bias introduced by the varying prevalence of specific patient populations in different epilepsy centers. We discuss the need for a multi-institutional study that combines features from different imaging modalities as well as computational techniques to definitively assess the utility of specific automated approaches to epilepsy imaging. We conclude that sharing and comparing these different computational techniques through a common data platform provides an opportunity to rigorously test and compare the accuracy of these tools across different patient populations and geographical locations. We propose that these kinds of tools, quantitative imaging analysis methods and open data platforms for aggregating and sharing data and algorithms, can play a vital role in reducing the cost of care, the risks of invasive treatments, and improve overall outcomes for patients with epilepsy.

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We introduce common epileptogenic lesions encountered in patients with drug resistant epilepsy.

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We discuss state of the art computational techniques used to detect lesions.

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There is a need for multi-institutional studies that combine these techniques.

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Clinically validated pipelines alongside the advances in imaging and electrophysiology will improve outcomes.

Mild Malformation of Cortical Development with Oligodendroglial Hyperplasia in Frontal Lobe Epilepsy: A New Clinico-Pathological Entity

The histopathological spectrum of human epileptogenic brain lesions is widespread including common and rare variants of cortical malformations. However, 2-26% of epilepsy surgery specimens are histopathologically classified as nonlesional. We hypothesized that these specimens include also new diagnostic entities, in particular when presurgical magnetic resonance imaging (MRI) can identify abnormal signal intensities within the anatomical region of seizure onset. In our series of 1381 en bloc resected epilepsy surgery brain specimens, 52 cases could not be histopathologically classified and were considered nonlesional (3.7%). An increase of Olig2-, and PDGFR-alpha-immunoreactive oligodendroglia was observed in white matter and deep cortical layers in 22 of these patients (42%). Increased proliferation activity as well as heterotopic neurons in white matter were additional histopathological hallmarks. All patients suffered from frontal lobe epilepsy (FLE) with a median age of epilepsy onset at 4 years and 16 years at epilepsy surgery. Presurgical MRI suggested focal cortical dysplasia (FCD) in all patients. We suggest to classify this characteristic histopathology pattern as "mild malformation of cortical development with oligodendroglial hyperplasia (MOGHE)." Further insights into pathomechanisms of MOGHE may help to bridge the diagnostic gap in children and young adults with difficult-to-treat FLE.

Genes that Affect Brain Structure and Function Identified by Rare Variant Analyses of Mendelian Neurologic Disease

Development of the human nervous system involves complex interactions among fundamental cellular processes and requires a multitude of genes, many of which remain to be associated with human disease. We applied whole exome sequencing to 128 mostly consanguineous families with neurogenetic disorders that often included brain malformations. Rare variant analyses for both single nucleotide variant (SNV) and copy number variant (CNV) alleles allowed for identification of 45 novel variants in 43 known disease genes, 41 candidate genes, and CNVs in 10 families, with an overall potential molecular cause identified in >85% of families studied. Among the candidate genes identified, we found PRUNE, VARS, and DHX37 in multiple families and homozygous loss-of-function variants in AGBL2, SLC18A2, SMARCA1, UBQLN1, and CPLX1. Neuroimaging and in silico analysis of functional and expression proximity between candidate and known disease genes allowed for further understanding of genetic networks underlying specific types of brain malformations.

Whole-exome sequencing is a powerful approach for establishing the etiological diagnosis in patients with intellectual disability and microcephaly

Background

Clinical and genetic heterogeneity in monogenetic disorders represents a major diagnostic challenge. Although the presence of particular clinical features may aid in identifying a specific cause in some cases, the majority of patients remain undiagnosed.

Here, we investigated the utility of whole-exome sequencing as a diagnostic approach for establishing a molecular diagnosis in a highly heterogeneous group of patients with varied intellectual disability and microcephaly.

Methods

Whole-exome sequencing was performed in 38 patients, including three sib-pairs, in addition to or in parallel with genetic analyses that were performed during the diagnostic work-up of the study participants.

Results

In ten out of these 35 families (29 %), we found mutations in genes already known to be related to a disorder in which microcephaly is a main feature. Two unrelated patients had mutations in the ASPM gene. In seven other patients we found mutations in RAB3GAP1, RNASEH2B, KIF11, ERCC8, CASK, DYRK1A and BRCA2. In one of the sib-pairs, mutations were found in the RTTN gene. Mutations were present in seven out of our ten families with an established etiological diagnosis with recessive inheritance.

Conclusions

We demonstrate that whole-exome sequencing is a powerful tool for the diagnostic evaluation of patients with highly heterogeneous neurodevelopmental disorders such as intellectual disability with microcephaly. Our results confirm that autosomal recessive disorders are highly prevalent among patients with microcephaly.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-016-0167-8) contains supplementary material, which is available to authorized users.

Optimization of MRI-based scoring scales of brain injury severity in children with unilateral cerebral palsy

BACKGROUND

Several scoring systems for measuring brain injury severity have been developed to standardize the classification of MRI results, which allows for the prediction of functional outcomes to help plan effective interventions for children with cerebral palsy.

OBJECTIVE

The aim of this study is to use statistical techniques to optimize the clinical utility of a recently proposed template-based scoring method by weighting individual anatomical scores of injury, while maintaining its simplicity by retaining only a subset of scored anatomical regions.

MATERIALS AND METHODS

Seventy-six children with unilateral cerebral palsy were evaluated in terms of upper limb motor function using the Assisting Hand Assessment measure and injuries visible on MRI using a semiquantitative approach. This cohort included 52 children with periventricular white matter injury and 24 with cortical and deep gray matter injuries. A subset of the template-derived cerebral regions was selected using a data-driven region selection algorithm. Linear regression was performed using this subset, with interaction effects excluded.

RESULTS

Linear regression improved multiple correlations between MRI-based and Assisting Hand Assessment scores for both periventricular white matter (R squared increased to 0.45 from 0, P < 0.0001) and cortical and deep gray matter (0.84 from 0.44, P < 0.0001) cohorts. In both cohorts, the data-driven approach retained fewer than 8 of the 40 template-derived anatomical regions.

CONCLUSION

The equal or better prediction of the clinically meaningful Assisting Hand Assessment measure using fewer anatomical regions highlights the potential of these developments to enable enhanced quantification of injury and prediction of patient motor outcome, while maintaining the clinical expediency of the scoring approach.

Whole-brain MRI phenotyping in dysplasia-related frontal lobe epilepsy

OBJECTIVE

To perform whole-brain morphometry in patients with frontal lobe epilepsy and evaluate the utility of group-level patterns for individualized diagnosis and prognosis.

METHODS

We compared MRI-based cortical thickness and folding complexity between 2 frontal lobe epilepsy cohorts with histologically verified focal cortical dysplasia (FCD) (13 type I; 28 type II) and 41 closely matched controls. Pattern learning algorithms evaluated the utility of group-level findings to predict histologic FCD subtype, the side of the seizure focus, and postsurgical seizure outcome in single individuals.

RESULTS

Relative to controls, FCD type I displayed multilobar cortical thinning that was most marked in ipsilateral frontal cortices. Conversely, type II showed thickening in temporal and postcentral cortices. Cortical folding also diverged, with increased complexity in prefrontal cortices in type I and decreases in type II. Group-level findings successfully guided automated FCD subtype classification (type I: 100%; type II: 96%), seizure focus lateralization (type I: 92%; type II: 86%), and outcome prediction (type I: 92%; type II: 82%).

CONCLUSION

FCD subtypes relate to diverse whole-brain structural phenotypes. While cortical thickening in type II may indicate delayed pruning, a thin cortex in type I likely results from combined effects of seizure excitotoxicity and the primary malformation. Group-level patterns have a high translational value in guiding individualized diagnostics.

Clinical Profile of Pediatric Neurological Disorders: Outpatient Department, Khartoum, Sudan

BACKGROUND

There is no available data from Sudan reflecting the magnitude of the neurological disorders and disabilities in the pediatric age-group. This study aims to evaluate the pattern of neurological disorders among Sudanese children.

PATIENTS AND METHODS

This is a retrospective survey of children with epilepsy and other neurodisability disorders seen at pediatric neurology outpatient clinic, during the period from January 2007 to August 2013. The data of 9600 patients were analyzed.

RESULTS

A total of 6019 patients were included in the study. The majority of the patients had epilepsy that amounted to 52.8%, followed by cerebral palsy (19.1%), congenital anomalies of the central nervous system (6.2%), neuromuscular disorders (3.2%), stroke (2.4%), ataxia and movement disorders (1.9%), assumed genetic syndromes (1.2%), and others.

CONCLUSION

Neurological disorders constitute a major cause of chronic morbidity in pediatric age-group.

Neuroimaging of epilepsy

Imaging is pivotal in the evaluation and management of patients with seizure disorders. Elegant structural neuroimaging with magnetic resonance imaging (MRI) may assist in determining the etiology of focal epilepsy and demonstrating the anatomical changes associated with seizure activity. The high diagnostic yield of MRI to identify the common pathological findings in individuals with focal seizures including mesial temporal sclerosis, vascular anomalies, low-grade glial neoplasms and malformations of cortical development has been demonstrated. Positron emission tomography (PET) is the most commonly performed interictal functional neuroimaging technique that may reveal a focal hypometabolic region concordant with seizure onset. Single photon emission computed tomography (SPECT) studies may assist performance of ictal neuroimaging in patients with pharmacoresistant focal epilepsy being considered for neurosurgical treatment. This chapter highlights neuroimaging developments and innovations, and provides a comprehensive overview of the imaging strategies used to improve the care and management of people with epilepsy.

Neuroepidemiology of Porencephaly, Schizencephaly, and Hydranencephaly in Miyagi Prefecture, Japan

BACKGROUND

No population-based surveys of porencephaly, schizencephaly, and hydranencephaly have been conducted in Japan or other Asian countries. We performed a neuroepidemiologic analysis to elucidate the incidence of porencephaly, schizencephaly, and hydranencephaly in Miyagi prefecture, Japan, during 2007-2011.

METHODS

We sent inquiry forms in February 2012 to three neonatal intensive care units, 25 divisions of orthopedic surgery in municipal hospitals, 33 divisions of pediatrics including one university hospital, municipal hospitals, pediatric practitioners, and institutions for physically handicapped children located in Miyagi prefecture. These covered all clinics related to pediatric neurology and orthopedic surgery in Miyagi prefecture. In the inquiry, diagnostic criteria for porencephaly, schizencephaly, and hydranencephaly were described and representative images of magnetic resonance imaging were shown. We obtained an 82% (27 of 33) response rate from the divisions of pediatrics, a 100% (3 of 3) response rate from the neonatal intensive care units, and a 68% (17 of 25) response rate from orthopedic surgery clinics. The magnetic resonance imaging scans of each patient were retrieved and inspected.

RESULTS

Five, one, and two individuals developed porencephaly, schizencephaly, and hydranencephaly, respectively. The estimated incidence rates of porencephaly, schizencephaly, and hydranencephaly were 5.2 (95% confidence interval [CI], 0.6-9.8), 1.0 (95% CI, 0.0-3.1), and 2.1 (95% CI, 0.0-5.0) per 100,000 live births, respectively.

CONCLUSIONS

The prevalence rates of porencephaly, schizencephaly, and hydranencephaly at birth reported herein are compatible with results reported previously in the United States and European countries. The overall prevalence rate of these three diseases was 8.3 (95% CI, 2.6-14.1) per 100,000 live births.

Normal development

Numerous events are involved in brain development, some of which are detected by neuroimaging. Major changes in brain morphology are depicted by brain imaging during the fetal period while changes in brain composition can be demonstrated in both pre- and postnatal periods. Although ultrasonography and computed tomography can show changes in brain morphology, these techniques are insensitive to myelination that is one of the most important events occurring during brain maturation. Magnetic resonance imaging (MRI) is therefore the method of choice to evaluate brain maturation. MRI also gives insight into the microstructure of brain tissue through diffusion-weighted imaging and diffusion tensor imaging. Metabolic changes are also part of brain maturation and are assessed by proton magnetic resonance spectroscopy. Understanding and knowledge of the different steps in brain development are required to be able to detect morphologic and structural changes on neuroimaging. Consequently alterations in normal development can be depicted.

Validation of In utero Tractography of Human Fetal Commissural and Internal Capsule Fibers with Histological Structure Tensor Analysis

Diffusion tensor imaging (DTI) and tractography offer the unique possibility to visualize the developing white matter macroanatomy of the human fetal brain in vivo and in utero and are currently under investigation for their potential use in the diagnosis of developmental pathologies of the human central nervous system. However, in order to establish in utero DTI as a clinical imaging tool, an independent comparison between macroscopic imaging and microscopic histology data in the same subject is needed. The present study aimed to cross-validate normal as well as abnormal in utero tractography results of commissural and internal capsule fibers in human fetal brains using postmortem histological structure tensor (ST) analysis. In utero tractography findings from two structurally unremarkable and five abnormal fetal brains were compared to the results of postmortem ST analysis applied to digitalized whole hemisphere sections of the same subjects. An approach to perform ST-based deterministic tractography in histological sections was implemented to overcome limitations in correlating in utero tractography to postmortem histology data. ST analysis and histology-based tractography of fetal brain sections enabled the direct assessment of the anisotropic organization and main fiber orientation of fetal telencephalic layers on a micro- and macroscopic scale, and validated in utero tractography results of corpus callosum and internal capsule fiber tracts. Cross-validation of abnormal in utero tractography results could be achieved in four subjects with agenesis of the corpus callosum (ACC) and in two cases with malformations of internal capsule fibers. In addition, potential limitations of current DTI-based in utero tractography could be demonstrated in several brain regions. Combining the three-dimensional nature of DTI-based in utero tractography with the microscopic resolution provided by histological ST analysis may ultimately facilitate a more complete morphologic characterization of axon guidance disorders at prenatal stages of human brain development.

Pränataldiagnostik bei fetaler Mikrozephalie

Diese Übersichtsarbeit behandelt die Mikrozephalie (MZ) aus der Perspektive der pränatalen Diagnostik. Eine MZ wird bei einem Kopfumfang unter der dritten Standardabweichung für das Gestationsalter vermutet. Diese Verdachtsdiagnose kann aus einem falschen Gestationsalter oder einer falsche Messung resultieren oder infolge einer Reihe häufiger Ätiologien wie offene Spina bifida, Enzephalozele, Holoprosenzephalie, Infektion, Aneuploidie, seltener auch Ursachen wie einer primären oder syndromalen MZ entstehen. Typische Ultraschallzeichen einer fetalen MZ sind die flache Stirn, der kleine Frontallappen, das reduzierte Gyrierungsmuster mit einem kurzen Balken, eine Pseudo-Kraniosynostose, ein dilatierter Subarachnoidalraum und oft eine Diskrepanz zwischen Kopf- und Bauchumfang. Mitunter kann eine schwere MZ schon in der Mitte der Schwangerschaft entdeckt werden, aber die meisten Formen fallen erst im III. Trimenon bzw. nach der Geburt auf. Die diagnostische Abklärung sollte auch das Angebot genetischer Untersuchungen einschließen, um monogen vererbte Formen mit hohem Wiederholungsrisiko z. B. bei autosomal-rezessiver Vererbung zu identifizieren. Die Arbeit diskutiert pränatalmedizinische und genetisch-diagnostische Abklärungsschritte bei fetaler MZ, die in Kombination mit den neuen genetischen Untersuchungstechniken hoffentlich in Zukunft zu einer höheren Aufklärungsrate führen werden.

Immunity and Inflammation in Epilepsy

This review reports the available evidence on the activation of the innate and adaptive branches of the immune system and the related inflammatory processes in epileptic disorders and the putative pathogenic role of inflammatory processes developing in the brain, as indicated by evidence from experimental and clinical research. Indeed, there is increasing knowledge supporting a role of specific inflammatory mediators and immune cells in the generation and recurrence of epileptic seizures, as well as in the associated neuropathology and comorbidities. Major challenges in this field remain: a better understanding of the key inflammatory pathogenic pathways activated in chronic epilepsy and during epileptogenesis, and how to counteract them efficiently without altering the homeostatic tissue repair function of inflammation. The relevance of this information for developing novel therapies will be highlighted.

Strukturelle Hirnfehlbildungen mit Mikrozephalie

Hirnfehlbildungen sind ein häufiger Befund bei Mikrozephalien, ihr Nachweis erhöht die Wahrscheinlichkeit einer genetisch bedingten Grunderkrankung. Werden weitere Zusatzsymptome wie Entwicklungsverzögerung oder Epilepsie beobachtet, sollte frühzeitig eine zerebrale Bildgebung möglichst mittels MRT und neuroradiologischer Beurteilung veranlasst werden. Insbesondere Hinweise auf eine Holoprosenzephalie oder neuronale Migrationsstörungen können die Einleitung zielführender genetischer Untersuchungen bahnen. In diesem Artikel sollen für häufigere Formen syndromaler und nicht-syndromaler Mikrozephalien mit wichtigen neuroradiologischen Leitbefunden wie periventrikulären Heterotopien, Lissenzephalie, Double Cortex, Holoprosenzephalie, pontozerebelläre Hypoplasien und Agenesie oder Hypoplasie des Corpus callosum differenzialdiagnostische Überlegungen und diagnostische Algorithmen vorgestellt werden.

"Who is talking to me?" - Self-other attribution of auditory hallucinations and sulcation of the right temporoparietal junction

Brain imaging research in schizophrenia has provided a better understanding of the neural basis of auditory hallucinations (AH). Recently, renewed interest in the phenomenology of AH raised questions related to their neural substrates. Hence, the neural basis of AH self/other attribution have yet to be investigated as beliefs regarding the origin of the voices is a cardinal feature of AH phenomenology. As the right temporoparietal junction (TPJ) and the inferior parietal lobule (IPL) play a key role in disentangling the origin of sensory events and in self/other distinction, we tested the hypothesis that the morphology of the IPL/TPJ area may be involved in AH self/other attribution. Magnetic resonance images of 39 right-handed patients with persistent auditory hallucinations and 19 healthy subjects were analyzed with sulcus-based morphometry. AH self-other attribution were found to be associated with the sulcal pattern of the posterior part of the Sylvian fissure, encompassing the IPL/TPJ area. The preference for the attribution of AH to self or to others could be associated with early neurodevelopmental events as the sulcal pattern is determined during fetal life and is stable after birth. Our study also raises basic cognitive questions regarding self-consciousness and suggest that impairments at a pre-reflexive level, leading to hearing his/her thoughts as voices ('I' level or feeling of agency), and a reflexive level leading to attribution belief ('Me' level or judgment of agency) are likely involved in AH.

Genes and brain malformations associated with abnormal neuron positioning

Neuronal positioning is a fundamental process during brain development. Abnormalities in this process cause several types of brain malformations and are linked to neurodevelopmental disorders such as autism, intellectual disability, epilepsy, and schizophrenia. Little is known about the pathogenesis of developmental brain malformations associated with abnormal neuron positioning, which has hindered research into potential treatments. However, recent advances in neurogenetics provide clues to the pathogenesis of aberrant neuronal positioning by identifying causative genes. This may help us form a foundation upon which therapeutic tools can be developed. In this review, we first provide a brief overview of neural development and migration, as they relate to defects in neuronal positioning. We then discuss recent progress in identifying genes and brain malformations associated with aberrant neuronal positioning during human brain development.

Anterior and posterior complexes: a step towards improving neurosonographic screening of midline and cortical anomalies

OBJECTIVE

To describe the anatomical structures that form the anterior (AC) and posterior (PC) complexes of the fetal brain and to categorize their anomalies in fetuses with cerebral abnormalities.

METHODS

We analyzed retrospectively volume datasets from 100 normal fetuses between 20 and 30 weeks' gestation. On the axial transventricular plane, our analysis of the AC included the interhemispheric fissure (IHF), the callosal sulcus (CS), the genu of the corpus callosum (CC), the cavum septi pellucidi (CSP) and the anterior horns (AH) of the lateral ventricles. The PC included the splenium of the CC, the medial wall of the lateral ventricles, the CS and the parieto-occipital fissure (POF). We then categorized AC/PC findings in 32 fetuses with agenesis of the septi pellucidi, schizencephaly, callosal dysgenesis, cortical malformation and hypoxic-ischemic brain injury.

RESULTS

The structures forming the AC and PC were visible in 100% and 92%, respectively, of normal cases. In the AC, the CSP was square-shaped in 73% of cases and it was triangular in 27%; the AH was comma-shaped in 92% of cases and triangular in the remainder. In the PC, the splenium of the CC interrupted and bridged the midline and was delimited posteriorly by the CS and the IHF. The POF was visible posteriorly. We categorized AC and PC abnormalities according to the main deviation from normality in their anatomical structures. The AC was abnormal in 30/32 cases and the PC was abnormal in 16/32 cases. In the two cases with normal AC, the PC was abnormal.

CONCLUSION

Normal appearance of AC and PC seems to be a strong indicator of fetal central nervous system normality. Morphological abnormalities in both complexes are robust markers of midline defects, but not exclusively so. The majority of fetuses with cortical malformations showed a defect in the AC.

Apical versus Basal Neurogenesis Directs Cortical Interneuron Subclass Fate

Fate determination in the mammalian telencephalon, with its diversity of neuronal subtypes and relevance to neuropsychiatric disease, remains a critical area of study in neuroscience. Most studies investigating this topic focus on the diversity of neural progenitors within spatial and temporal domains along the lateral ventricles. Often overlooked is whether the location of neurogenesis within a fate-restricted domain is associated with, or instructive for, distinct neuronal fates. Here, we use in vivo fate mapping and the manipulation of neurogenic location to demonstrate that apical versus basal neurogenesis influences the fate determination of major subgroups of cortical interneurons derived from the subcortical telencephalon. Somatostatin-expressing interneurons arise mainly from apical divisions along the ventricular surface, whereas parvalbumin-expressing interneurons originate predominantly from basal divisions in the subventricular zone. As manipulations that shift neurogenic location alter interneuron subclass fate, these results add an additional dimension to the spatial-temporal determinants of neuronal fate determination.

Malformations of cortical development: 3T magnetic resonance imaging features

Malformation of cortical development (MCD) is a term representing an inhomogeneous group of central nervous system abnormalities, referring particularly to embriyological aspect as a consequence of any of the three developmental stages, i.e., cell proliferation, cell migration and cortical organization. These include cotical dysgenesis, microcephaly, polymicrogyria, schizencephaly, lissencephaly, hemimegalencephaly, heterotopia and focal cortical dysplasia. Since magnetic resonance imaging is the modality of choice that best identifies the structural anomalies of the brain cortex, we aimed to provide a mini review of MCD by using 3T magnetic resonance scanner images.

Ezh2 is involved in radial neuronal migration through regulating Reelin expression in cerebral cortex

Radial migration of pyramidal neurons is an important event during the development of cerebral cortex. Neurons experience series of morphological and directional transitions to get to their final laminar positions. Here we report that the histone methyltransferase enhancer of zest homolog 2 (Ezh2) is involved in the regulation of cortical radial migration. We show that Ezh2 knockdown leads to disturbed neuronal orientation, which results in the impairment of radial migration. Further results reveal that this migration deficiency may be due to the derepression of Reelin transcription in the migrating neurons. Our study provides evidence that epigenetic regulation of Reelin by Ezh2 maintains appropriate Reelin expression pattern to fulfill proper orientation of migrating neurons.

TUBA1A mutation can cause a hydranencephaly-like severe form of cortical dysgenesis

TUBA1A mutations cause a wide spectrum of lissencephaly and brain malformations. Here, we report two patients with severe cortical dysgeneses, one with an extremely thin cerebral parenchyma apparently looking like hydranencephaly and the other with lissencephaly accompanied by marked hydrocephalus, both harbouring novel de novo missense mutations of TUBA1A. To elucidate how the various TUBA1A mutations affect the severity of the phenotype, we examined the capacity of the mutant protein to incorporate into the endogenous microtubule network in transfected COS7 cells by measuring line density using line extraction in an immunofluorescence study. The mutants responsible for severe phenotypes were found to incorporate extensively into the network. To determine how each mutant alters the microtubule stability, we examined cold-induced microtubule depolymerisation in fibroblasts. The depolymerisation of patients’ fibroblasts occurred earlier than that of control fibroblasts, suggesting that microtubules bearing mutated tubulins are unstable. Both mutations are predicted to participate in lateral interactions of microtubules. Our data suggest that the TUBA1A mutations disrupting lateral interactions have pronounced dominant-negative effects on microtubule dynamics that are associated with the severe end of the lissencephaly spectrum.

Pathophysiological analyses of cortical malformation using gyrencephalic mammals

One of the most prominent features of the cerebral cortex of higher mammals is the presence of gyri. Because malformations of the cortical gyri are associated with severe disability in brain function, the mechanisms underlying malformations of the cortical gyri have been of great interest. Combining gyrencephalic carnivore ferrets and genetic manipulations using in utero electroporation, here we successfully recapitulated the cortical phenotypes of thanatophoric dysplasia (TD) by expressing fibroblast growth factor 8 in the ferret cerebral cortex. Strikingly, in contrast to TD mice, our TD ferret model showed not only megalencephaly but also polymicrogyria. We further uncovered that outer radial glial cells (oRGs) and intermediate progenitor cells (IPs) were markedly increased. Because it has been proposed that increased oRGs and/or IPs resulted in the appearance of cortical gyri during evolution, it seemed possible that increased oRGs and IPs underlie the pathogenesis of polymicrogyria. Our findings should help shed light on the molecular mechanisms underlying the formation and malformation of cortical gyri in higher mammals.

47 patients with FLNA associated periventricular nodular heterotopia

Background

Heterozygous loss of function mutations within the Filamin A gene in Xq28 are the most frequent cause of bilateral neuronal periventricular nodular heterotopia (PVNH). Most affected females are reported to initially present with difficult to treat seizures at variable age of onset. Psychomotor development and cognition may be normal or mildly to moderately impaired. Distinct associated extracerebral findings have been observed and may help to establish the diagnosis including patent ductus arteriosus Botalli, progressive dystrophic cardiac valve disease and aortic dissection, chronic obstructive lung disease or chronic constipation. Genotype-phenotype correlations could not yet be established.

Methods

Sanger sequencing and MLPA was performed for a large cohort of 47 patients with Filamin A associated PVNH (age range 1 to 65 years). For 34 patients more detailed clinical information was available from a structured questionnaire and medical charts on family history, development, epileptologic findings, neurological examination, cognition and associated clinical findings. Available detailed cerebral MR imaging was assessed for 20 patients.

Results

Thirty-nine different FLNA mutations were observed, they are mainly truncating (37/39) and distributed throughout the entire coding region. No obvious correlation between the number and extend of PVNH and the severity of the individual clinical manifestation was observed. 10 of the mutation carriers so far are without seizures at a median age of 19.7 years. 22 of 24 patients with available educational data were able to attend regular school and obtain professional education according to age.

Conclusions

We report the clinical and mutation spectrum as well as MR imaging for a large cohort of 47 patients with Filamin A associated PVNH including two adult males. Our data are reassuring in regard to psychomotor and cognitive development, which is within normal range for the majority of patients. However, a concerning median diagnostic latency of 17 to 20 years was noted between seizure onset and the genetic diagnosis, intensely delaying appropriate medical surveillance for potentially life threatening cardiovascular complications as well as genetic risk assessment and counseling prior to family planning for this X-linked dominant inherited disorder with high perinatal lethality in hemizygous males.

Malformations of cortical development and epilepsy: A cohort of 150 patients in western China

PURPOSE

Malformations of cortical development (MCDs) are abnormalities of the cerebral cortex that arise from abnormal formation of the cortical plate, and have become increasingly identified as an important etiology for refractory epilepsy. Little is known about the spectrum, distribution and clinical features of MCDs, especially in resource-limited regions. This study investigates the distribution of MCDs and compares the clinical features and long-term prognosis between the two forms of MCDs: Simple and Multiple.

METHOD

One hundred and fifty epilepsy patients (138 adults, 12 pediatric patients) with radiologically diagnosed MCDs were identified at a tertiary epilepsy center in western China. Patients were divided into three subtypes according to the Barkovich classification. They were further divided into either Simple or Multiple MCD forms based on whether they had a single type of MCDs or other co-existing developmental brain abnormalities.

RESULTS

The most common type of MCD is focal cortical dysplasia. We found perinatal insults more common in group III patients. Multiple MCD was identified in 36 of 150 patients, and was associated with higher rates of delayed milestones (p=0.005), cognitive impairment (p=0.023) and neurological deficits (p=0.002) compared to Simple MCD. Extra-temporal epilepsy was more commonly seen among individuals with Multiple MCD (p=0.017). Participants with Multiple MCD were younger at time of seizure onset (p=0.003) and at assessment (p=0.002), had a lower seizure-free rate (p=0.033) and had worse outcomes overall. Patients with heterotopias were more commonly associated with other abnormalities.

CONCLUSION

MCDs are a critical cause of epilepsy and pose a big challenge for resource-limited countries. Imaging techniques are crucial in diagnosing and classifying cortical deformities. Multiple malformations lead to more severe clinical features and worse prognosis. Identifying and classifying MCDs can help physicians to better estimate patient prognosis and seek the best, individualized therapeutic options.

Fetal MRI detects early alterations of brain development in Tetralogy of Fallot

OBJECTIVE

Prenatal imaging has identified alterations of brain growth in fetuses with congenital heart disease. However, little is known about the timing of altered brain development and its occurrence in specific congenital heart disease subgroups. This magnetic resonance imaging study aimed to identify early (median, 25 gestational weeks [GW]) changes in fetal total brain (TBV), gray matter (GMV), and subcortical brain (SBV) volumes in Tetralogy of Fallot (TOF) cases in utero.

STUDY DESIGN

Fetal magnetic resonance imaging (1.5 Tesla) was performed in 24 fetuses who were diagnosed with TOF and 24 normal age-matched control fetuses (20-34 GW). TBV, GMV, SBV, intracranial cavity, cerebellar, ventricular, and external cerebrospinal fluid volumes were quantified by manual segmentation based on coronal T2-weighted sequences. Mixed model analyses of variance and t-tests were conducted to compare cases and control fetuses.

RESULTS

TBV was significantly lower (P < .001) in early (<25 GW) and late TOF cases. Both GMV (P = .003) and SBV (P = .001) were affected. The GMV-to-SBV ratio declined in fetuses with TOF (P = .026). Compared with normal fetuses, ventricular volume was increased (P = .0048). External cerebrospinal fluid was enlarged in relation to head size (P < .001). Intracranial cavity volume (P = .314) and cerebellar volume (P = .074) were not significantly reduced in fetuses with TOF.

CONCLUSION

TOF is associated with smaller volumes of gray and white matter and enlarged cerebrospinal fluid spaces. These changes are present at ≤25 GW and indicate altered fetal brain growth in this pathophysiologic entity during early stages of human brain development.

Language comprehension in nonspeaking children with severe cerebral palsy: Neuroanatomical substrate?

BACKGROUND AND AIMS

To identify relations between brain abnormalities and spoken language comprehension, MRI characteristics of 80 nonspeaking children with severe CP were examined.

METHODS

MRI scans were analysed for patterns of brain abnormalities and scored for specific MRI measures: white matter (WM) areas; size of lateral ventricles, WM abnormality/reduction, cysts, subarachnoid space, corpus callosum thinning and grey matter (GM) areas; cortical GM abnormalities, thalamus, putamen, globus pallidus and nucleus caudatus and cerebellar abnormalities. Language comprehension was assessed with a new validated instrument (C-BiLLT).

RESULTS

MRI scans of 35 children were classified as a basal ganglia necrosis (BGN) pattern, with damage to central GM areas; in 60% of these children damage to WM areas was also found. MRI scans of 13 children were classified as periventricular leukomalacia (PVL) with little concomitant damage to central GM areas, 13 as malformations and 19 as miscellaneous. Language comprehension was best in children with BGN, followed by malformations and miscellaneous, and was poorest in PVL. Linear regression modelling per pattern group (malformations excluded), with MRI measures as independent variables, revealed that corpus callosum thinning in BGN and parieto-occipital WM reduction in PVL were the most important explanatory factors for poor language comprehension. No MRI measures explained outcomes in language comprehension in the miscellaneous group.

CONCLUSIONS

Comprehension of spoken language differs between MRI patterns of severe CP. In children with BGN and PVL differences in language comprehension performance is attributed to damage in the WM areas. Language comprehension was most affected in children with WM lesions in the subcortical and then periventricular areas, most characteristic for children with PVL.

Epilepsy: A Spectrum Disorder

Epilepsy, a disorder of unprovoked seizures is a multifaceted disease affecting individuals of all ages with a particular predilection for the very young and old. In addition to seizures, many patients often report cognitive and psychiatric problems associated with both the seizures themselves and its therapy. Epilepsy has numerous etiologies both idiopathic and acquired with a wide range of therapeutic responses. Despite numerous treatments available to control repetitive seizures including medications, diets, immunotherapy, surgery, and neuromodulatory devices, a large percentage of patients continue to suffer the consequences of uncontrolled seizures, which include psychosocial stigma and death.

Extracellular and Intracellular Signaling for Neuronal Polarity

Neurons are one of the highly polarized cells in the body. One of the fundamental issues in neuroscience is how neurons establish their polarity; therefore, this issue fascinates many scientists. Cultured neurons are useful tools for analyzing the mechanisms of neuronal polarization, and indeed, most of the molecules important in their polarization were identified using culture systems. However, we now know that the process of neuronal polarization in vivo differs in some respects from that in cultured neurons. One of the major differences is their surrounding microenvironment; neurons in vivo can be influenced by extrinsic factors from the microenvironment. Therefore, a major question remains: How are neurons polarized in vivo? Here, we begin by reviewing the process of neuronal polarization in culture conditions and in vivo. We also survey the molecular mechanisms underlying neuronal polarization. Finally, we introduce the theoretical basis of neuronal polarization and the possible involvement of neuronal polarity in disease and traumatic brain injury.

Neuronal migration disorders: Focus on the cytoskeleton and epilepsy

A wide spectrum of focal, regional, or diffuse structural brain abnormalities, collectively known as malformations of cortical development (MCDs), frequently manifest with intellectual disability (ID), epilepsy, and/or autistic spectrum disorder (ASD). As the acronym suggests, MCDs are perturbations of the normal architecture of the cerebral cortex and hippocampus. The pathogenesis of these disorders remains incompletely understood; however, one area that has provided important insights has been the study of neuronal migration. The amalgamation of human genetics and experimental studies in animal models has led to the recognition that common genetic causes of neurodevelopmental disorders, including many severe epilepsy syndromes, are due to mutations in genes regulating the migration of newly born post-mitotic neurons. Neuronal migration genes often, though not exclusively, code for proteins involved in the function of the cytoskeleton. Other cellular processes, such as cell division and axon/dendrite formation, which similarly depend on cytoskeletal functions, may also be affected. We focus here on how the susceptibility of the highly organized neocortex and hippocampus may be due to their laminar organization, which involves the tight regulation, both temporally and spatially, of gene expression, specialized progenitor cells, the migration of neurons over large distances and a birthdate-specific layering of neurons. Perturbations in neuronal migration result in abnormal lamination, neuronal differentiation defects, abnormal cellular morphology and circuit formation. Ultimately this results in disorganized excitatory and inhibitory activity leading to the symptoms observed in individuals with these disorders.

Brain imaging and genetic risk in the pediatric population, part 1: inherited metabolic diseases

In this article, the genotype-MR phenotype correlation of the most common or clinically important inherited metabolic diseases (IMD) in the pediatric population is reviewed. A nonsystematic search of the PubMed/Medline database of relevant studies about "genotype-phenotype correlation" in IMD was performed. Some MR phenotypes related to specific gene mutations were found, such as bilateral hypertrophy of inferior olives in patients harboring POLG and SURF1 mutations, and central lesions in the cervical spinal cord in patients with nonketotic hyperglycinemia harboring GLRX5 gene mutation.