Lissencephaly: Expanded imaging and clinical classification

1q21.1 distal copy number variants are associated with cerebral and cognitive alterations in humans

Low-frequency 1q21.1 distal deletion and duplication copy number variant (CNV) carriers are predisposed to multiple neurodevelopmental disorders, including schizophrenia, autism and intellectual disability. Human carriers display a high prevalence of micro- and macrocephaly in deletion and duplication carriers, respectively. The underlying brain structural diversity remains largely unknown. We systematically called CNVs in 38 cohorts from the large-scale ENIGMA-CNV collaboration and the UK Biobank and identified 28 1q21.1 distal deletion and 22 duplication carriers and 37,088 non-carriers (48% male) derived from 15 distinct magnetic resonance imaging scanner sites. With standardized methods, we compared subcortical and cortical brain measures (all) and cognitive performance (UK Biobank only) between carrier groups also testing for mediation of brain structure on cognition. We identified positive dosage effects of copy number on intracranial volume (ICV) and total cortical surface area, with the largest effects in frontal and cingulate cortices, and negative dosage effects on caudate and hippocampal volumes. The carriers displayed distinct cognitive deficit profiles in cognitive tasks from the UK Biobank with intermediate decreases in duplication carriers and somewhat larger in deletion carriers-the latter potentially mediated by ICV or cortical surface area. These results shed light on pathobiological mechanisms of neurodevelopmental disorders, by demonstrating gene dose effect on specific brain structures and effect on cognitive function.

Fundamental functional differences between gyri and sulci: implications for brain function, cognition, and behavior

Folding of the cerebral cortex is a prominent characteristic of mammalian brains. Alterations or deficits in cortical folding are strongly correlated with abnormal brain function, cognition, and behavior. Therefore, a precise mapping between the anatomy and function of the brain is critical to our understanding of the mechanisms of brain structural architecture in both health and diseases. Gyri and sulci, the standard nomenclature for cortical anatomy, serve as building blocks to make up complex folding patterns, providing a window to decipher cortical anatomy and its relation with brain functions. Huge efforts have been devoted to this research topic from a variety of disciplines including genetics, cell biology, anatomy, neuroimaging, and neurology, as well as involving computational approaches based on machine learning and artificial intelligence algorithms. However, despite increasing progress, our understanding of the functional anatomy of gyro-sulcal patterns is still in its infancy. In this review, we present the current state of this field and provide our perspectives of the methodologies and conclusions concerning functional differentiation between gyri and sulci, as well as the supporting information from genetic, cell biology, and brain structure research. In particular, we will further present a proposed framework for attempting to interpret the dynamic mechanisms of the functional interplay between gyri and sulci. Hopefully, this review will provide a comprehensive summary of anatomo-functional relationships in the cortical gyro-sulcal system together with a consideration of how these contribute to brain function, cognition, and behavior, as well as to mental disorders.

A novel TUBG1 mutation with neurodevelopmental disorder caused by malformations of cortical development

Neurodevelopmental disorder caused by malformations of cortical development is a rare neurological disease. Heterozygous missense variants in the TUBG1 gene lead to malformations of human cortical development, which further result in intellectual disability, developmental retardation, and epilepsy. To the best of our knowledge, only thirteen patients and a total of nine pathogenic TUBG1 variants have been described in the published literature. This study reports the case details and genetic data analysis of a girl (aged 8 years, 9 months) with developmental delay, psychomotor regression, epilepsy, and left external ear deformity. A novel TUBG1 mutation was identified by whole-exome sequencing and Sanger sequencing, confirming that this mutation may be the cause of the neurodevelopmental disorders. This case report characterizes the phenotypic spectrum, molecular genetic findings, and functional consequences of novel pathogenic TUBG1 variants in neurodevelopmental disorders caused by cortical development malformations.

Definitions and classification of malformations of cortical development: practical guidelines

Malformations of cortical development are a group of rare disorders commonly manifesting with developmental delay, cerebral palsy or seizures. The neurological outcome is extremely variable depending on the type, extent and severity of the malformation and the involved genetic pathways of brain development. Neuroimaging plays an essential role in the diagnosis of these malformations, but several issues regarding malformations of cortical development definitions and classification remain unclear. The purpose of this consensus statement is to provide standardized malformations of cortical development terminology and classification for neuroradiological pattern interpretation. A committee of international experts in paediatric neuroradiology prepared systematic literature reviews and formulated neuroimaging recommendations in collaboration with geneticists, paediatric neurologists and pathologists during consensus meetings in the context of the European Network Neuro-MIG initiative on Brain Malformations (https://www.neuro-mig.org/). Malformations of cortical development neuroimaging features and practical recommendations are provided to aid both expert and non-expert radiologists and neurologists who may encounter patients with malformations of cortical development in their practice, with the aim of improving malformations of cortical development diagnosis and imaging interpretation worldwide.

Variants in KIF2A cause broad clinical presentation; the computational structural analysis of a novel variant in a patient with a cortical dysplasia, complex, with other brain malformations 3

Cortical dysplasia, complex, with other brain malformations 3 (CDCBM3) is a rare autosomal dominant syndrome caused by Kinesin family Member 2A (KIF2A) gene mutation. Patients with CDCBM3 exhibit posterior dominant agyria/pachygyria with severe motor dysfunction. Here, we report an 8-year-old boy with CDCBM3 showing a typical, but relatively mild, clinical presentation of CDCBM3 features. Whole-exome sequencing identified a heterozygous mutation of NM_001098511.2:c.1298C>A [p.(Ser433Tyr)]. To our knowledge, the mutation has never been reported previously. The variant was located distal to the nucleotide binding domain (NBD), in which previously-reported variants in CDCBM3 patients have been located. The computational structural analysis showed the p.433 forms the pocket with NBD. Variants in KIF2A have been reported in the NBD for CDCBM3, in the kinesin motor 3 domain, but not in the NBD in epilepsy, and outside of the kinesin motor domain in autism spectrum syndrome, respectively. Our patient has a variant, that is not in the NBD but at the pocket with the NBD, resulting in a clinical features of CDCBM3 with mild symptoms. The clinical findings of patients with KIF2A variants appear restricted to the central nervous system and facial anomalies. We can call this spectrum "KIF2A syndrome" with variable severity.

Lissencephaly in an epilepsy cohort: Molecular, radiological and clinical aspects

INTRODUCTION

Lissencephaly is a rare malformation of cortical development due to abnormal transmantle migration resulting in absent or reduced gyration. The lissencephaly spectrum consists of agyria, pachygyria and subcortical band heterotopia. In this study we compared genetic aetiology, neuroradiology, clinical phenotype and response to antiepileptic drugs in patients with epilepsy and lissencephaly spectrum malformations.

METHODS

The study group consisted of 20 patients - 13 males and 7 females, aged 18 months to 21 years at the time of data collection. Genetic testing was performed by oligonucleotide array comparative genomic hybridization (microarray), multiplex ligation-dependent probe amplification (MLPA), targeted gene panels and whole exome/genome sequencing. All neuroradiological investigations were re-evaluated and the malformations were classified by the same neuroradiologist. Clinical features and response to anti-epileptic drugs (AEDs) were evaluated by retrospective review of medical records.

RESULTS

In eleven patients (55%) mutations in PAFAH1B1 (LIS1) or variable microdeletions of 17p13.3 including the PAFAH1B1 gene were detected. Four patients (20%) had tubulin encoding gene mutations (TUBA1A, TUBG1 and TUBGCP6). Mutations in DCX, DYNC1H1, ADGRG1 and WDR62 were identified in single patients. In one patient, a possibly pathogenic intragenic deletion in TRIO was detected. A clear radiologic distinction could be made between tubulinopathies and PAFAH1B1 related lissencephaly. The majority of the patients had therapy resistant epilepsy and epileptic spasms was the most prominent seizure type. The best therapeutic response to seizure control in our cohort was obtained by the ketogenic diet, vigabatrin, clobazam, phenobarbital and valproate.

CONCLUSION

The most common genetic aetiologies in our cohort of 20 individuals with epilepsy and lissencephaly spectrum were intragenic deletions or single nucleotide mutations in PAFAH1B1 or larger deletions in 17p13.3, encompassing PAFAH1B1, followed by mutations in tubulin encoding genes. Radiological findings could reliably predict molecular results only in agyria with a posterior to anterior gradient. Radiological and molecular findings did not correlate consistently with severity of clinical outcome or therapeutic response.

Emergence of non-canonical parvalbumin-containing interneurons in hippocampus of a murine model of type I lissencephaly

Type I lissencephaly is a neuronal migration disorder caused by haploinsuffiency of the PAFAH1B1 (mouse: Pafah1b1) gene and is characterized by brain malformation, developmental delays, and epilepsy. Here, we investigate the impact of Pafah1b1 mutation on the cellular migration, morphophysiology, microcircuitry, and transcriptomics of mouse hippocampal CA1 parvalbumin-containing inhibitory interneurons (PV+INTs). We find that WT PV+INTs consist of two physiological subtypes (80% fast-spiking (FS), 20% non-fast-spiking (NFS)) and four morphological subtypes. We find that cell-autonomous mutations within interneurons disrupts morphophysiological development of PV+INTs and results in the emergence of a non-canonical 'intermediate spiking (IS)' subset of PV+INTs. We also find that now dominant IS/NFS cells are prone to entering depolarization block, causing them to temporarily lose the ability to initiate action potentials and control network excitation, potentially promoting seizures. Finally, single-cell nuclear RNAsequencing of PV+INTs revealed several misregulated genes related to morphogenesis, cellular excitability, and synapse formation.

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.

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.

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.

Aberrant sorting of hippocampal complex pyramidal cells in type I lissencephaly alters topological innervation

Layering has been a long-appreciated feature of higher order mammalian brain structures but the extent to which it plays an instructive role in synaptic specification remains unknown. Here we examine the formation of synaptic circuitry under cellular heterotopia in hippocampal CA1, using a mouse model of the human neurodevelopmental disorder Type I Lissencephaly. We identify calbindin-expressing principal cells which are mispositioned under cellular heterotopia. Ectopic calbindin-expressing principal cells develop relatively normal morphological features and stunted intrinsic physiological features. Regarding network development, a connectivity preference for cholecystokinin-expressing interneurons to target calbindin-expressing principal cells is diminished. Moreover, in vitro gamma oscillatory activity is less synchronous across heterotopic bands and mutants are less responsive to pharmacological inhibition of cholecystokinin-containing interneurons. This study will aid not only in our understanding of how cellular networks form but highlight vulnerable cellular circuit motifs that might be generalized across disease states.

Autosomal dominant TUBB3-related syndrome: Fetal, radiologic, clinical and morphological features

OBJECTIVE

To describe fetal, clinical, radiological, morphological features of TUBB3 related syndrome.

METHODS

We report two families each of two generations harboring a novel and a previously described heterozygous TUBB3 pathogenic variants. We compared these patients with other published TUBB3-related cases. We describe the pathological features of dysgyria in the two aborted fetuses.

RESULTS

The mother and son from family 1 had a history of mild developmental delay in motor and language skills and demonstrated mild cerebellar signs and mirror movements. Neuroimaging findings included: hypoplastic corpus callosum (CC), asymmetric ventriculomegaly and cerebellar vermis hypoplasia in all patients and frontal dysgyria in three. Autopsy of the fetal brain showed an unusual shape and orientation of the frontal sulci and gyri with normal cortical layering and no abnormal cell types. The mother of family 2 had congenital strabismus, mild muscle weakness on the right and a past history of developmental delay. Fetal brain MRI showed abnormal cerebral sulcation, hemispheric asymmetry, asymmetric ventriculomegaly, dysmorphic short CC and frontal cortical interdigitation. Autopsy demonstrated fronto-parietal predominant dysgyria, bilateral ventriculomegaly, hippocampal and CC hypoplasia, abnormal Sylvian fissure. Lamination and neuron morphology in the areas of dysgyria were normal.

CONCLUSIONS

TUBB3 related cortical malformations can be mild, consistent with dysgyria rather than typical pachygyria or polymicrogyria. The autopsy findings in fetal TUBB3 related dysgyria are abnormal orientation of sulci and gyri, but normal neuron morphology and layering. We suggest that TUBB3 - associated brain malformations can be suspected in-utero which in turn can aid in prognostic counselling and interpretation of genetic testing.

Pathogenic Variants in CEP85L Cause Sporadic and Familial Posterior Predominant Lissencephaly

Lissencephaly (LIS), denoting a "smooth brain," is characterized by the absence of normal cerebral convolutions with abnormalities of cortical thickness. Pathogenic variants in over 20 genes are associated with LIS. The majority of posterior predominant LIS is caused by pathogenic variants in LIS1 (also known as PAFAH1B1), although a significant fraction remains without a known genetic etiology. We now implicate CEP85L as an important cause of posterior predominant LIS, identifying 13 individuals with rare, heterozygous CEP85L variants, including 2 families with autosomal dominant inheritance. We show that CEP85L is a centrosome protein localizing to the pericentriolar material, and knockdown of Cep85l causes a neuronal migration defect in mice. LIS1 also localizes to the centrosome, suggesting that this organelle is key to the mechanism of posterior predominant LIS.

Posterior Neocortex-Specific Regulation of Neuronal Migration by CEP85L Identifies Maternal Centriole-Dependent Activation of CDK5

Genes mutated in human neuronal migration disorders encode tubulin proteins and a variety of tubulin-binding and -regulating proteins, but it is very poorly understood how these proteins function together to coordinate migration. Additionally, the way in which regional differences in neocortical migration are controlled is completely unknown. Here we describe a new syndrome with remarkably region-specific effects on neuronal migration in the posterior cortex, reflecting de novo variants in CEP85L. We show that CEP85L is required cell autonomously in vivo and in vitro for migration, that it localizes to the maternal centriole, and that it forms a complex with many other proteins required for migration, including CDK5, LIS1, NDE1, KIF2A, and DYNC1H1. Loss of CEP85L disrupts CDK5 localization and activation, leading to centrosome disorganization and disrupted microtubule cytoskeleton organization. Together, our findings suggest that CEP85L highlights a complex that controls CDK5 activity to promote neuronal migration.

Fetal Neuroimaging Update

OBJECTIVES

To review the current imaging techniques available for the evaluation of the fetal brain.

FINDINGS

Ultrasound remains the initial screening modality with routine scanning typically performed at 18-20 weeks gestation. When a central nervous system (CNS) abnormality is noted by ultrasound, MRI is increasingly being used to further clarify findings. Fetal MRI has the unique ability to provide high detailed anatomical information of the entire human fetus with high contrast resolution. This technique has grown due to the development of rapid single shot image acquisition sequences, improvement of motion correction strategies and optimizing shimming techniques.

CONCLUSIONS

The assessment of fetal CNS anomalies continues to improve. Advanced MRI techniques have allowed for further delineation of CNS anomalies and have become a cornerstone in the assessment of fetal brain well-being. Those interpreting fetal studies need to be familiar with the strengths and limitations of each exam and be sensitive to the impact discussing findings can have regarding perinatal care and delivery planning. Collaboration with neurologists, neurosurgeons, geneticists, counselors, and maternal fetal specialists are key in providing the best care to the families we treat.

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.

Exploring classification of birth defects severity in national hospital discharge databases compared to an active surveillance program

OBJECTIVE

To explore the extent to which the severity of birth defects could be differentiated using severity of illness (SOI) and risk of mortality (ROM) measures available in national discharge databases.

METHODS

Data from the 2012-14 National Inpatient Sample (NIS) was used to identify hospitalizations with one or more major birth defects reported annually to the National Birth Defects Prevention Network using the International Classification of Diseases, Ninth Edition, Clinical Modification (ICD-9-CM) diagnosis codes. Each hospitalization also contained a 4-level SOI and 4-level ROM classification measure. For each birth defect and for each individual birth defect-related ICD-9-CM code, we calculated mean and median SOI and ROM, the proportion of hospitalizations in each level of SOI and ROM, the inpatient mortality rate, and level of agreement between various existing or derived severity proxies in the NIS and the Texas Birth Defects Registry (TBDR).

RESULTS

Mean SOI ranged from 1.5 (cleft lip alone) to 3.7 (single ventricle), and mean ROM ranged from 1.1 (cleft lip alone) to 3.9 (anencephaly). As a group, critical congenital heart defects had the highest average number of co-occurring defects, mean SOI, and ROM, whereas orofacial and genitourinary defects had the lowest SOI and ROM. We found strong levels of agreement between TBDR severity classifications and NIS severity classifications defined using Level 3 or 4 SOI or ROM Level 3 or 4.

CONCLUSIONS

This preliminary investigation demonstrated how severity indices of birth defects could be differentiated and compared to a severity algorithm of an existing surveillance program.

Differential distributions of parvalbumin-positive interneurons in the sulci and gyri of the adult ferret cerebral cortex

Although accumulating evidence suggests that there are significant anatomical and histological differences between the sulci and gyri of the cerebral cortex, whether there is a difference in the distribution of interneurons between the two cortical regions remains largely unknown. In this study, we systematically compared the distributions of parvalbumin-positive interneurons among three neighboring gyrus and sulcus pairs-coronal gyrus and cruciate sulcus, anterior ectosylvian gyrus and rostral suprasylvian sulcus, and posterior ectosylvian gyrus and pseudosylvian sulcus-in the adult ferret cerebral cortex. We proposed a method to partition sulci and gyri into several specific subregions through the deepest points of the sulci and the highest points of gyri in the inner and outer cortical contours of coronal sections. We found that the density of parvalbumin-positive interneurons in the gyri was significantly higher than that in the sulci. Further study revealed that the density of PV interneurons in superficial cortical layers (layers 2/3 and layer 4) was comparable among the three pairs of sulci and gyri. However, the density of parvalbumin-positive interneurons in cortical layers 5/6 was significantly higher in gyri than in sulci. These results indicate that parvalbumin-positive interneurons are differently distributed in infragranular layers of cortical sulci and gyri.

Subcortical heterotopic gray matter brain malformations: Classification study of 107 individuals

OBJECTIVE

To better evaluate the imaging spectrum of subcortical heterotopic gray matter brain malformations (subcortical heterotopia [SUBH]), we systematically reviewed neuroimaging and clinical data of 107 affected individuals.

METHODS

SUBH is defined as heterotopic gray matter, located within the white matter between the cortex and lateral ventricles. Four large brain malformation databases were searched for individuals with these malformations; data on imaging, clinical outcomes, and results of molecular testing were systematically reviewed and integrated with all previously published subtypes to create a single classification system.

RESULTS

Review of the databases revealed 107 patients with SUBH, the large majority scanned during childhood (84%), including more than half before 4 years (59%). Although most individuals had cognitive or motor disability, 19% had normal development. Epilepsy was documented in 69%. Additional brain malformations were common and included abnormalities of the corpus callosum (65/102 [64%]), and, often, brainstem or cerebellum (47/106 [44%]). Extent of the heterotopic gray matter brain malformations (unilateral or bilateral) did not influence the presence or age at onset of seizures. Although genetic testing was not systematically performed in this group, the sporadic occurrence and frequent asymmetry suggests either postzygotic mutations or prenatal disruptive events. Several rare, bilateral forms are caused by mutations in genes associated with cell proliferation and polarity (EML1, TUBB, KATNB1, CENPJ, GPSM2).

CONCLUSION

This study reveals a broad clinical and imaging spectrum of heterotopic malformations and provides a framework for their classification.

Structural and Diffusion MRI Analyses With Histological Observations in Patients With Lissencephaly

The development of cortical convolutions, gyri and sulci, is a complex process that takes place during prenatal development. Lissencephaly, a rare genetic condition characterized by the lack of cortical convolutions, offers a model to look into biological processes that lead to the development of convolutions. Retrospective, qualitative, and quantitative analyses of structural magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) were performed in patients with lissencephaly (N = 10) and age-/sex-matched controls (N = 10). In order to identify microstructural correlates of structural MRI and DTI findings, postmortem brains of patients with lissencephaly (N = 4) and age-matched controls (N = 4) were also examined with histology. Patients with lissencephaly had significantly smaller gyrification index and volumes of hemispheric white and gray matter, compared to the age-/sex-matched control group. However, there was no significant difference between groups in the subcortical gray matter volumes. Although the majority of patients with lissencephaly had a preserved normal-like appearance of major fissures and primary sulci, the spatial distribution of agyric cortical regions was different in patients with lissencephaly-1 (LIS1) and doublecortin (DCX) mutations. Lastly, in patients with lissencephaly, the spatiotemporal distribution of projection pathways was preserved while short- to medium-range cortico-cortical pathways were absent or fewer in number. Our results indicate that in the patients with lissencephaly cortical system is affected more than the subcortical one.

Phenotypic spectrum associated with a CRADD founder variant underlying frontotemporal predominant pachygyria in the Finnish population

Intellectual disability (ID), megalencephaly, frontal predominant pachygyria, and seizures, previously called "thin" lissencephaly, are reported to be caused by recessive variants in CRADD. Among five families of different ethnicities identified, one homozygous missense variant, c.509G>A p.(Arg170His), was of Finnish ancestry. Here we report on the phenotypic variability associated for this potential CRADD founder variant in 22 Finnish individuals. Exome sequencing was used to identify candidate genes in Finnish patients presenting with ID. Targeted Sanger sequencing and restriction enzyme analysis were applied to screen for the c.509G>A CRADD variant in cohorts from Finland. Detailed phenotyping and genealogical studies were performed. Twenty two patients were identified with the c.509G>A p.(Arg170His) homozygous variant in CRADD. The majority of the ancestors originated from Northeastern Finland indicating a founder effect. The hallmark of the disease is frontotemporal predominant pachygyria with mild cortical thickening. All patients show ID of variable severity. Aggressive behavior was found in nearly half of the patients, EEG abnormalities in five patients and megalencephaly in three patients. This study provides detailed data about the phenotypic spectrum of patients with lissencephaly due to a CRADD variant that affects function. High inter- and intrafamilial phenotypic heterogeneity was identified in patients with pachygyria caused by the homozygous CRADD founder variant. The phenotype variability suggests that additional genetic and/or environmental factors play a role in the clinical presentation. Since frontotemporal pachygyria is the hallmark of the disease, brain imaging studies are essential to support the molecular diagnosis for individuals with ID and a CRADD variant.

Tubulinopathies

Mutations causing dysfunction of the tubulins and microtubule-associated proteins, otherwise known as tubulinopathies, are a group of recently described entities, that lead to complex brain malformations. An understanding of the fundamental principles of operation of the cytoskeleton and compounds in particular microtubules, actin, and microtubule-associated proteins, can assist in the interpretation of the imaging findings of tubulinopathies. Somewhat consistent morphological imaging patterns have been described in tubulinopathies such as dysmorphic basal ganglia-the hallmark (found in 75% of cases), callosal dysgenesis, cerebellar hypoplasia/dysplasia, and cortical malformations, most notably lissencephaly. Recognizing the common imaging phenotypes present in tubulinopathies can prove invaluable in directing the genetic workup for a patient with brain malformations.

Malformations of Cerebral Cortex Development: Molecules and Mechanisms

Malformations of cortical development encompass heterogeneous groups of structural brain anomalies associated with complex neurodevelopmental disorders and diverse genetic and nongenetic etiologies. Recent progress in understanding the genetic basis of brain malformations has been driven by extraordinary advances in DNA sequencing technologies. For example, somatic mosaic mutations that activate mammalian target of rapamycin signaling in cortical progenitor cells during development are now recognized as the cause of hemimegalencephaly and some types of focal cortical dysplasia. In addition, research on brain development has begun to reveal the cellular and molecular bases of cortical gyrification and axon pathway formation, providing better understanding of disorders involving these processes. New neuroimaging techniques with improved resolution have enhanced our ability to characterize subtle malformations, such as those associated with intellectual disability and autism. In this review, we broadly discuss cortical malformations and focus on several for which genetic etiologies have elucidated pathogenesis.

Fetal neurology: Principles and practice with a life-course perspective

Clinical service, educational, and research components of a fetal/neonatal neurology program are anchored by the disciplines of developmental origins of health and disease and life-course science as programmatic principles. Prenatal participation provides perspectives on maternal, fetal, and placental contributions to health or disease for fetal and subsequent neonatal neurology consultations. This program also provides an early-life diagnostic perspective for neurologic specialties concerned with brain health and disease throughout childhood and adulthood. Animal models and birth cohort studies have demonstrated how the science of epigenetics helps to understand gene-environment interactions to better predict brain health or disease. Fetal neurology consultations provide important diagnostic contributions during critical or sensitive periods of brain development when future neurotherapeutic interventions will maximize adaptive neuroplasticity. Age-specific normative neuroinformatics databases that employ computer-based strategies to integrate clinical/demographic, neuroimaging, neurophysiologic, and genetic datasets will more accurately identify either symptomatic patients or those at risk for brain disorders who would benefit from preventive, rescue, or reparative treatment choices throughout the life span.

Fetal and neonatal neurogenetics

Disorders of the developing nervous system may be of genetic origin, comprising congenital malformations of spine and brain as well as metabolic or vascular disorders that affect normal brain development. Acquired causes include congenital infections, hypoxic-ischemic or traumatic brain injury, and a number of rare neoplasms. This chapter focuses on the clinical presentation and workup of neurogenetic disorders presenting in the fetal or neonatal period. After a summary of the most frequent clinical presentations, clues from history taking and clinical examination are illustrated with short case reports. This is followed by a discussion of the different tools available for the workup of neurogenetic disorders, including the various genetic techniques with their advantages and disadvantages. The implications of a molecular genetic diagnosis for the patient and family are addressed in the section on counseling. The chapter concludes with a proposed workflow that may help the clinician when confronted with a potential neurogenetic disorder in the fetal or neonatal period.

MACF1 Mutations Encoding Highly Conserved Zinc-Binding Residues of the GAR Domain Cause Defects in Neuronal Migration and Axon Guidance

To date, mutations in 15 actin- or microtubule-associated genes have been associated with the cortical malformation lissencephaly and variable brainstem hypoplasia. During a multicenter review, we recognized a rare lissencephaly variant with a complex brainstem malformation in three unrelated children. We searched our large brain-malformation databases and found another five children with this malformation (as well as one with a less severe variant), analyzed available whole-exome or -genome sequencing data, and tested ciliogenesis in two affected individuals. The brain malformation comprised posterior predominant lissencephaly and midline crossing defects consisting of absent anterior commissure and a striking W-shaped brainstem malformation caused by small or absent pontine crossing fibers. We discovered heterozygous de novo missense variants or an in-frame deletion involving highly conserved zinc-binding residues within the GAR domain of MACF1 in the first eight subjects. We studied cilium formation and found a higher proportion of mutant cells with short cilia than of control cells with short cilia. A ninth child had similar lissencephaly but only subtle brainstem dysplasia associated with a heterozygous de novo missense variant in the spectrin repeat domain of MACF1. Thus, we report variants of the microtubule-binding GAR domain of MACF1 as the cause of a distinctive and most likely pathognomonic brain malformation. A gain-of-function or dominant-negative mechanism appears likely given that many heterozygous mutations leading to protein truncation are included in the ExAC Browser. However, three de novo variants in MACF1 have been observed in large schizophrenia cohorts.

Analysis of 17 genes detects mutations in 81% of 811 patients with lissencephaly

PURPOSE

To estimate diagnostic yield and genotype-phenotype correlations in a cohort of 811 patients with lissencephaly or subcortical band heterotopia.

METHODS

We collected DNA from 756 children with lissencephaly over 30 years. Many were tested for deletion 17p13.3 and mutations of LIS1, DCX, and ARX, but few other genes. Among those tested, 216 remained unsolved and were tested by a targeted panel of 17 genes (ACTB, ACTG1, ARX, CRADD, DCX, LIS1, TUBA1A, TUBA8, TUBB2B, TUBB, TUBB3, TUBG1, KIF2A, KIF5C, DYNC1H1, RELN, and VLDLR) or by whole-exome sequencing. Fifty-five patients studied at another institution were added as a validation cohort.

RESULTS

The overall mutation frequency in the entire cohort was 81%. LIS1 accounted for 40% of patients, followed by DCX (23%), TUBA1A (5%), and DYNC1H1 (3%). Other genes accounted for 1% or less of patients. Nineteen percent remained unsolved, which suggests that several additional genes remain to be discovered. The majority of unsolved patients had posterior pachygyria, subcortical band heterotopia, or mild frontal pachygyria.

CONCLUSION

The brain-imaging pattern correlates with mutations in single lissencephaly-associated genes, as well as in biological pathways. We propose the first LIS classification system based on the underlying molecular mechanisms.

Expanding the Distinctive Neuroimaging Phenotype of ACTA2 Mutations

BACKGROUND AND PURPOSE

Arg179His mutations in ACTA2 are associated with a distinctive neurovascular phenotype characterized by a straight course of intracranial arteries, absent basal Moyamoya collaterals, dilation of the proximal internal carotid arteries, and occlusive disease of the terminal internal carotid arteries. We now add to the distinctive neuroimaging features in these patients by describing their unique constellation of brain malformative findings that could flag the diagnosis in cases in which targeted cerebrovascular imaging has not been performed.

MATERIALS AND METHODS

Neuroimaging studies from 13 patients with heterozygous Arg179His mutations in ACTA2 and 1 patient with pathognomonic clinicoradiologic findings for ACTA2 mutation were retrospectively reviewed. The presence and localization of brain malformations and other abnormal brain MR imaging findings are reported.

RESULTS

Characteristics bending and hypoplasia of the anterior corpus callosum, apparent absence of the anterior gyrus cinguli, and radial frontal gyration were present in 100% of the patients; flattening of the pons on the midline and multiple indentations in the lateral surface of the pons were demonstrated in 93% of the patients; and apparent "squeezing" of the cerebral peduncles in 85% of the patients.

CONCLUSIONS

Because α-actin is not expressed in the brain parenchyma, only in vascular tissue, we speculate that rather than a true malformative process, these findings represent a deformation of the brain during development related to the mechanical interaction with rigid arteries during the embryogenesis.

Diagnostic value of partial exome sequencing in developmental disorders

Although intellectual disability is one of the major indications for genetic counselling, there are no homogenous diagnostic algorithms for molecular testing. While whole exome sequencing is increasingly applied, we questioned whether analyzing a partial exome, enriched for genes associated with Mendelian disorders, might be a valid alternative approach that yields similar detection rates but requires less sequencing capacities. Within this context 106 patients with different intellectual disability forms were analyzed for mutations in 4.813 genes after pre-exclusion of copy number variations by array-CGH. Subsequent variant interpretation was performed in accordance with the ACMG guidelines. By this, a molecular diagnosis was established in 34% of cases and candidate mutations were identified in additional 24% of patients. Detection rates of causative mutations were above 30%, regardless of further symptoms, except for patients with seizures (23%). We did not detect an advantage from partial exome sequencing for patients with severe intellectual disability (36%) as compared to those with mild intellectual disability (44%). Specific clinical diagnoses pre-existed for 20 patients. Of these, 5 could be confirmed and an additional 6 cases could be solved, but showed mutations in other genes than initially suspected. In conclusion partial exome sequencing solved >30% of intellectual disability cases, which is similar to published rates obtained by whole exome sequencing. The approach therefore proved to be a valid alternative to whole exome sequencing for molecular diagnostics in this cohort. The method proved equally suitable for both syndromic and non-syndromic intellectual disability forms of all severity grades.

Comprehensive genotype-phenotype correlation in lissencephaly

Malformations of cortical development (MCD) are a heterogenous group of disorders with diverse genotypic and phenotypic variations. Lissencephaly is a subtype of MCD caused by defect in neuronal migration, which occurs between 12 and 24 weeks of gestation. The continuous advancement in the field of molecular genetics in the last decade has led to identification of at least 19 lissencephaly-related genes, most of which are related to microtubule structural proteins (tubulin) or microtubule-associated proteins (MAPs). The aim of this review article is to bring together current knowledge of gene mutations associated with lissencephaly and to provide a comprehensive genotype-phenotype correlation. Illustrative cases will be presented to facilitate the understanding of the described genotype-phenotype correlation.

Case Report of Proliferative Peripheral Retinopathy in Two Familial Lissencephaly Infants with Miller-Dieker Syndrome

A complete ophthalmic examination is not routinely performed on infants with Miller-Dieker syndrome (MDS, chromosome 17p13.3 microdeletion). The authors present the cases of four cousins with MDS who also carried a 16p13.3 microduplication (not associated with Rubinstein-Taybi syndrome). Retinopathy of prematurity-like proliferative peripheral retinopathy (PPR) was detected in two male first cousins, but was not detected in the female half-cousins. PPR in the first infant resolved by 4 months, but the second infant's PPR progressed, requiring photocoagulation followed by lens-sparing vitrectomy. While ocular abnormalities are more prevalent and severe in other lissencephalopathies, the PPR in these MDS infants underscores the sight-saving potential of performing an ophthalmologic exam with early molecular testing for all lissencephaly infants.

Tubulinopathies continued: refining the phenotypic spectrum associated with variants in TUBG1

Tubulinopathies are a heterogeneous group of conditions with a wide spectrum of clinical severity resulting from variants in genes of the tubulin superfamily. Variants in TUBG1 have been described in three patients with posterior predominant pachygyria and microcephaly. We here report eight additional patients with four novel heterozygous variants in TUBG1 identified by next-generation sequencing (NGS) analysis. All had severe motor and cognitive impairment and all except one developed seizures in early life. The core imaging features included a pachygyric cortex with posterior to anterior gradient, enlarged lateral ventricles most pronounced over the posterior horns, and variable degrees of reduced white matter volume. Basal ganglia, corpus callosum, brainstem, and cerebellum were often normal, in contrast to patients with variants in other tubulin genes where these structures are frequently malformed. The imaging phenotype associated with variants in TUBG1 is therefore more in line with the phenotype resulting from variants in LIS1 (a.k.a. PAFAH1B1). This difference may, at least in part, be explained by gamma-tubulin’s physiological function in microtubule nucleation, which differs from that of alpha and beta-tubulin.

Genetik der kortikalen Fehlbildungen

Kortikale Malformationen sind vielfältig und stellen eine wichtige Ursache der geistigen Entwicklungsstörung und der Epilepsie dar. Die Ätiologie der kortikalen Fehlbildungen ist sehr heterogen und beinhaltet sowohl rein exogene Ursachen als auch chromosomale und monogene Erkrankungen. Eine effiziente genetische Diagnostik bedarf der akkuraten Interpretation des Magnetresonanztomographie(MRT)-Musters. Bei einigen klinischen Formen kann eine zielgerichtete Einzelgendiagnostik erfolgen, die anderen klinischen Entitäten erfordern dagegen eine komplexe Stufendiagnostik und können nur mittels Hochdurchsatzsequenzierung aufgeklärt werden. In diesem Beitrag werden die 4 häufigsten kortikalen Fehlbildungen im Hinblick auf die typischen klinischen Symptome, MRT-Merkmale und den Algorithmus der genetischen Abklärung vorgestellt.

Electroclinical Pattern and Epilepsy Evolution in an Infant with Miller-Dieker Syndrome

Aim of the study:

To evaluate the electroclinical course and the correlation Electroencephalographic (EEG) pattern and epileptic seizures in an infant with Miller Dieker Syndrome (MDS) during the first year of life.

Materials and Methods:

MDS was diagnosed in the infant soon after birth and followed up from six months of life to one year, at the Department of Pediatrics, General Pediatric Operative Unit, Policlinico Vittorio Emanuele, University Hospital, XCatania, Italy, with clinical and serial EEG recording.

Results:

Aside from severe delay in the developmental milestone, the onset of the seizures was first noticed by the parents at the age of 4 months as brief slow tonic movements; at 6 months as tonic movements of the upper limbs with a slow rotations of the trunk, i.e. “subtle spams”; and at 7 months as typical “infantile spams” and tonic seizures. The EEG recording registered pattern of modified hypsarrhythmia (MH) correlated with “subtle spams” at the age of 6 months and at the age of 7 months the same EEG recording of MH associated to clinical expression of classical Infantile Spams (IS).

Conclusions:

In this infant, the EEG pattern and epileptic seizures were widely variable ranging clinically from brief anomalous movements to “subtle spams” and to typical infantile spams. At the same time, the EEG recording manifested first with MH and one month later with classical hypsarrhythmia. The EEG recording MH correlated first with clinical expression of subtle spams and the EEG remaining unchanged with the classical clinical expression of infantile spams.