Neuropathology of brain and spinal malformations in a case of monosomy 1p36

Development of prefrontal cortex

During evolution, the cerebral cortex advances by increasing in surface and the introduction of new cytoarchitectonic areas among which the prefrontal cortex (PFC) is considered to be the substrate of highest cognitive functions. Although neurons of the PFC are generated before birth, the differentiation of its neurons and development of synaptic connections in humans extend to the 3rd decade of life. During this period, synapses as well as neurotransmitter systems including their receptors and transporters, are initially overproduced followed by selective elimination. Advanced methods applied to human and animal models, enable investigation of the cellular mechanisms and role of specific genes, non-coding regulatory elements and signaling molecules in control of prefrontal neuronal production and phenotypic fate, as well as neuronal migration to establish layering of the PFC. Likewise, various genetic approaches in combination with functional assays and immunohistochemical and imaging methods reveal roles of neurotransmitter systems during maturation of the PFC. Disruption, or even a slight slowing of the rate of neuronal production, migration and synaptogenesis by genetic or environmental factors, can induce gross as well as subtle changes that eventually can lead to cognitive impairment. An understanding of the development and evolution of the PFC provide insight into the pathogenesis and treatment of congenital neuropsychiatric diseases as well as idiopathic developmental disorders that cause intellectual disabilities.

The Neuropathology of 1p36 Deletion Syndrome: An Autopsy Case Series

1p36 deletion syndrome is the most common terminal deletion syndrome, manifesting clinically as abnormal facies and developmental delay with frequent cardiac, skeletal, urogenital, and renal abnormalities. Limited autopsy case reports describe the neuropathology of 1p36 deletion syndrome. The most extensive single case report described a spectrum of abnormalities, mostly related to abnormal neuronal migration. We report the largest published series of 1p36 autopsy cases, with an emphasis on neuropathologic findings. Our series consists of 3 patients: 2 infants (5-hours old and 23-days old) and 1 older child (11 years). Our patients showed abnormal cortical gyration together with a spectrum of neuronal migration abnormalities, including heterotopias and hippocampal abnormalities, as well as cerebellar hypoplasia. Our findings thus support the role of neuronal migration defects in the pathogenesis of cognitive defects in 1p36 deletion syndrome and broaden the reported neuropathologic spectrum of this common syndrome.

1p36 deletion syndrome: first case report in Morocco detected by fluorescence in situ hybridization

The 1p36 deletion syndrome results from a heterozygous deletion of the terminal chromosomal band of the short arm of chromosome 1. Monosomy 1p36 is the most common terminal deletion observed in men (1 in 5000 newborns), characterized by distinctive dysmorphia, delayed growth, psychomotor retardation, intellectual deficit, epilepsy and heart defects. Fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH-array) are currently the two best diagnostic techniques. The objective of this work is to take stock of the first Moroccan case of 1p36 deletion and to illustrate the role of the geneticist in the diagnosis and management of this syndrome. There is currently no effective medical treatment for this disease.

An ancestral 10-bp repeat expansion in VWA1 causes recessive hereditary motor neuropathy

The extracellular matrix comprises a network of macromolecules such as collagens, proteoglycans and glycoproteins. VWA1 (von Willebrand factor A domain containing 1) encodes a component of the extracellular matrix that interacts with perlecan/collagen VI, appears to be involved in stabilizing extracellular matrix structures, and demonstrates high expression levels in tibial nerve. Vwa1-deficient mice manifest with abnormal peripheral nerve structure/function; however, VWA1 variants have not previously been associated with human disease. By interrogating the genome sequences of 74 180 individuals from the 100K Genomes Project in combination with international gene-matching efforts and targeted sequencing, we identified 17 individuals from 15 families with an autosomal-recessive, non-length dependent, hereditary motor neuropathy and rare biallelic variants in VWA1. A single disease-associated allele p.(G25Rfs*74), a 10-bp repeat expansion, was observed in 14/15 families and was homozygous in 10/15. Given an allele frequency in European populations approaching 1/1000, the seven unrelated homozygote individuals ascertained from the 100K Genomes Project represents a substantial enrichment above expected. Haplotype analysis identified a shared 220 kb region suggesting that this founder mutation arose >7000 years ago. A wide age-range of patients (6-83 years) helped delineate the clinical phenotype over time. The commonest disease presentation in the cohort was an early-onset (mean 2.0 ± 1.4 years) non-length-dependent axonal hereditary motor neuropathy, confirmed on electrophysiology, which will have to be differentiated from other predominantly or pure motor neuropathies and neuronopathies. Because of slow disease progression, ambulation was largely preserved. Neurophysiology, muscle histopathology, and muscle MRI findings typically revealed clear neurogenic changes with single isolated cases displaying additional myopathic process. We speculate that a few findings of myopathic changes might be secondary to chronic denervation rather than indicating an additional myopathic disease process. Duplex reverse transcription polymerase chain reaction and immunoblotting using patient fibroblasts revealed that the founder allele results in partial nonsense mediated decay and an absence of detectable protein. CRISPR and morpholino vwa1 modelling in zebrafish demonstrated reductions in motor neuron axonal growth, synaptic formation in the skeletal muscles and locomotive behaviour. In summary, we estimate that biallelic variants in VWA1 may be responsible for up to 1% of unexplained hereditary motor neuropathy cases in Europeans. The detailed clinical characterization provided here will facilitate targeted testing on suitable patient cohorts. This novel disease gene may have previously evaded detection because of high GC content, consequential low coverage and computational difficulties associated with robustly detecting repeat-expansions. Reviewing previously unsolved exomes using lower QC filters may generate further diagnoses.

Molecular characterization of a 1p36 chromosomal duplication and in utero interference define ENO1 as a candidate gene for polymicrogyria

While chromosome 1p36 deletion syndrome is one of the most common terminal subtelomeric microdeletion syndrome, 1p36 microduplications are rare events. Polymicrogyria (PMG) is a brain malformation phenotype frequently present in patients with 1p36 monosomy. The gene whose haploinsufficiency could cause this phenotype remains to be identified. We used high-resolution arrayCGH in patients with various forms of PMG in order to identify chromosomal variants associated to the malformation and characterized the genes included in these regions in vitro and in vivo. We identified the smallest case of 1p36 duplication reported to date in a patient presenting intellectual disability, microcephaly, epilepsy, and perisylvian polymicrogyria. The duplicated segment is intrachromosomal, duplicated in mirror and contains two genes: enolase 1 (ENO1) and RERE, both disrupted by the rearrangement. Gene expression analysis performed using the patient cells revealed a reduced expression, mimicking haploinsufficiency. We performed in situ hybridization to describe the developmental expression profile of the two genes in mouse development. In addition, we used in utero electroporation of shRNAs to show that Eno1 inactivation in the rat causes a brain development defect. These experiments allowed us to define the ENO1 gene as the most likely candidate to contribute to the brain malformation phenotype of the studied patient and consequently a candidate to contribute to the malformations of the cerebral cortex observed in patients with 1p36 monosomy.

Imprinted genes in clinical exome sequencing: Review of 538 cases and exploration of mouse-human conservation in the identification of novel human disease loci

Human imprinting disorders cause a range of dysmorphic and neurocognitive phenotypes, and they may elude traditional molecular diagnosis such exome sequencing. The discovery of novel disorders related to imprinted genes has lagged behind traditional Mendelian disorders because current diagnostic technology, especially unbiased testing, has limited utility in their discovery. To identify novel imprinting disorders, we reviewed data for every human gene hypothesized to be imprinted, identified each mouse ortholog, determined its imprinting status in the mouse, and analyzed its function in humans and mice. We identified 17 human genes that are imprinted in both humans and mice, and have functional data in mice or humans to suggest that dysregulated expression would lead to an abnormal phenotype in humans. These 17 genes, along with known imprinted genes, were preferentially flagged 538 clinical exome sequencing tests. The identified genes were: DIRAS3 [1p31.3], TP73 [1p36.32], SLC22A3 [6q25.3], GRB10 [7p12.1], DDC [7p12.2], MAGI2 [7q21.11], PEG10 [7q21.3], PPP1R9A [7q21.3], CALCR [7q21.3], DLGAP2 [8p23.3], GLIS3 [9p24.2], INPP5F [10q26.11], ANO1 [11q13.3], SLC38A4 [12q13.11], GATM [15q21.1], PEG3 [19q13.43], and NLRP2 [19q13.42]. In the 538 clinical cases, eight cases (1.7%) reported variants in a causative known imprinted gene. There were 367/758 variants (48.4%) in imprinted genes that were not known to cause disease, but none of those variants met the criteria for clinical reporting. Imprinted disorders play a significant role in human disease, and additional human imprinted disorders remain to be discovered. Therefore, evolutionary conservation is a potential tool to identify novel genes involved in human imprinting disorders and to identify them in clinical testing.

WARP: A Unique Extracellular Matrix Component of Cartilage, Muscle, and Endothelial Cell Basement Membranes

The von Willebrand factor A-domain-related protein (WARP) encoded by the VWA1 gene, is an orphan extracellular matrix protein that is expressed in a subset of ECM structures but whose function is poorly understood. Here, recent advances on understanding VWA1/WARP will be reviewed including analysis of VWA1 reporter and global knock-out mice, interaction studies, and recent transcriptome analyses. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc.

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.

Electroclinical features of epilepsy monosomy 1p36 syndrome and their implications

OBJECTIVIES

Monosomy 1p36 syndrome is a recognized syndrome with multiple congenital anomalies; medical problems of this syndrome include developmental delay, facial dysmorphisms, hearing loss, short stature, brain anomalies, congenital heart defects. Epilepsy can be another feature but there are few data about the types of seizures and long term prognosis. The aim of this work was to analyse the electroclinical phenotype and the long-term outcome in patients with monosomy 1p36 syndrome and epilepsy.

MATERIALS AND METHODS

Data of 22 patients with monosomy 1p36 syndrome and epilepsy were reconstructed by reviewing medical records. For each patient we analysed age at time of diagnosis, first signs of the syndrome, age at seizure onset, seizure type and its frequency, EEG and neuroimaging findings, the response to antiepileptic drugs treatment and clinical outcome up to the last follow-up assessment.

RESULTS

Infantile Spasm (IS) represents the most frequent type at epilepsy onset, which occurs in 36.4% of children, and a half of these were associated with hypsarrhythmic electroencephalogram. All patients with IS had persistence of seizures, unlike other patients with different seizures onset. Children with abnormal brain neuroimaging have a greater chance to develop pharmacoresistant epilepsy.

CONCLUSION

This syndrome represents a significant cause of IS: these patients, who develop IS, can suffer from pharmacoresistent epilepsy, that is more frequent in children with brain abnormalities.

Rer1-mediated quality control system is required for neural stem cell maintenance during cerebral cortex development

Rer1 is a retrieval receptor for endoplasmic reticulum (ER) retention of various ER membrane proteins and unassembled or immature components of membrane protein complexes. However, its physiological functions during mammalian development remain unclear. This study aimed to investigate the role of Rer1-mediated quality control system in mammalian development. We show that Rer1 is required for the sufficient cell surface expression and activity of γ-secretase complex, which modulates Notch signaling during mouse cerebral cortex development. When Rer1 was depleted in the mouse cerebral cortex, the number of neural stem cells decreased significantly, and malformation of the cerebral cortex was observed. Rer1 loss reduced γ-secretase activity and downregulated Notch signaling in the developing cerebral cortex. In Rer1-deficient cells, a subpopulation of γ-secretase complexes and components was transported to and degraded in lysosomes, thereby significantly reducing the amount of γ-secretase complex on the cell surface. These results suggest that Rer1 maintains Notch signaling by maintaining sufficient expression of the γ-secretase complex on the cell surface and regulating neural stem cell maintenance during cerebral cortex development.

We showed that Rer1 functions as an early-Golgi quality control pathway that maintains γ-secretase activity by maintaining sufficient cell surface expression of γ-secretase complex during cerebral cortex development, thereby modulating Notch signaling.

Electroclinical features of epilepsy associated with 1p36 deletion syndrome: A review

1p36 terminal deletion is a recently recognized syndrome with multiple congenital anomalies and intellectual disability. It occurs approximately in 1 out of 5000 to 10,000 live births and is the most common subtelomeric microdeletion observed in human. Medical problems commonly caused by terminal deletions of 1p36 include developmental delay, intellectual disability, seizures, vision problems, hearing loss, short stature, brain anomalies, congenital heart defects, cardiomyopathy, renal anomalies and distinctive facial features. Although the syndrome is considered clinically recognizable, there is significant phenotypic variation among affected individuals. Genotype-phenotype correlation in this syndrome is complicated, because of the similar clinical evidence seen in patients with different deletion sizes. We review 34 scientific articles from 1996 to 2016 that described 315 patients with 1p36 delection syndrome. The aim of this review is to find a correlation between size of the 1p36-deleted segments and the neurological clinical phenotypes with the analysis of electro-clinical patterns associated with chromosomal aberrations, that is a major tool in the identification of epilepsy susceptibility genes. Our finding suggest that developmental delay and early epilepsy are frequent findings in 1p36 deletion syndrome that can contribute to a poor clinical outcome for this reason this syndrome should be searched for in patients presenting with infantile spasms associated with a hypsarrhythmic EEG, particulary if they are combined with dismorphic features, severe hypotonia and developmental delay.

Genome-wide Analysis of the Role of Copy Number Variation in Schizophrenia Risk in Chinese

BACKGROUND

Compelling evidence suggested the role of copy number variations (CNVs) in schizophrenia susceptibility. Most of the evidence was from studies in populations with European ancestry. We tried to validate the associated CNV loci in a Han Chinese population and identify novel loci conferring risk of schizophrenia.

METHODS

We performed a genome-wide CNV analysis on 6588 patients with schizophrenia and 11,904 control subjects of Han Chinese ancestry.

RESULTS

Our data confirmed increased genome-wide CNV (>500 kb and <1%) burden in schizophrenia, and the increasing trend was more significant when only >1 Mb CNVs were considered. We also replicated several associated loci that were previously identified in European populations, including duplications at 16p11.2, 15q11.2-13.1, 7q11.23, and VIPR2 and deletions at 22q11.2, 1q21.1-q21.2, and NRXN1. In addition, we discovered three additional new potential loci (odds ratio >6, p < .05): duplications at 1p36.32, 10p12.1, and 13q13.3, involving many neurodevelopmental and synaptic related genes.

CONCLUSIONS

Our findings provide further support for the role of CNVs in the etiology of schizophrenia.

Malformations of cortical development and epilepsy

Malformations of cortical development (MCDs) are an important cause of epilepsy and an extremely interesting group of disorders from the perspective of brain development and its perturbations. Many new MCDs have been described in recent years as a result of improvements in imaging, genetic testing, and understanding of the effects of mutations on the ability of their protein products to correctly function within the molecular pathways by which the brain functions. In this review, most of the major MCDs are reviewed from a clinical, embryological, and genetic perspective. The most recent literature regarding clinical diagnosis, mechanisms of development, and future paths of research are discussed.

Polymicrogyria: pathology, fetal origins and mechanisms

Polymicrogyria (PMG) is a complex cortical malformation which has so far defied any mechanistic or genetic explanation. Adopting a broad definition of an abnormally folded or festooned cerebral cortical neuronal ribbon, this review addresses the literature on PMG and the mechanisms of its development, as derived from the neuropathological study of many cases of human PMG, a large proportion in fetal life. This reveals the several processes which appear to be involved in the early stages of formation of polymicrogyric cortex. The most consistent feature of developing PMG is disruption of the brain surface with pial defects, over-migration of cells, thickening and reduplication of the pial collagen layers and increased leptomeningeal vascularity. Evidence from animal models is consistent with our observations and supports the notion that disturbance in the formation of the leptomeninges or loss of their normal signalling functions are potent contributors to cortical malformation. Other mechanisms which may lead to PMG include premature folding of the neuronal band, abnormal fusion of adjacent gyri and laminar necrosis of the developing cortex. The observation of PMG in association with other and better understood forms of brain malformation, such as cobblestone cortex, suggests mechanistic pathways for some forms of PMG. The role of altered physical properties of the thickened leptomeninges in exerting mechanical constraints on the developing cortex is also considered.

Growth and folding of the mammalian cerebral cortex: from molecules to malformations

The size and extent of folding of the mammalian cerebral cortex are important factors that influence a species' cognitive abilities and sensorimotor skills. Studies in various animal models and in humans have provided insight into the mechanisms that regulate cortical growth and folding. Both protein-coding genes and microRNAs control cortical size, and recent progress in characterizing basal progenitor cells and the genes that regulate their proliferation has contributed to our understanding of cortical folding. Neurological disorders linked to disruptions in cortical growth and folding have been associated with novel neurogenetic mechanisms and aberrant signalling pathways, and these findings have changed concepts of brain evolution and may lead to new medical treatments for certain disorders.