Genetic disorders associated with postnatal microcephaly

A new type of blood-brain barrier aminoacidopathy underlies metabolic microcephaly associated with SLC1A4 mutations

Mutations in the SLC1A4 transporter lead to neurodevelopmental impairments, spastic tetraplegia, thin corpus callosum and microcephaly in children. SLC1A4 catalyses obligatory amino acid exchange between neutral amino acids, but the physiopathology of SLC1A4 disease mutations and progressive microcephaly remain unclear. Here, we examined the phenotype and metabolic profile of three Slc1a4 mouse models: a constitutive Slc1a4-knockout mouse; a knock-in mouse with the major human Slc1a4 mutation (Slc1a4-K256E); and a selective knockout of Slc1a4 in brain endothelial cells (Slc1a4tie2-cre). We show that Slc1a4 is a bona fideL-serine transporter at the blood-brain barrier (BBB) and that acute inhibition or deletion of Slc1a4 leads to a decrease in serine influx into the brain. This results in microcephaly associated with decreased L-serine content in the brain, accumulation of atypical and cytotoxic 1-deoxysphingolipids, neurodegeneration, synaptic and mitochondrial abnormalities and behavioural impairments. Prenatal and early postnatal oral administration of L-serine at levels that replenish the serine pool in the brain rescued the observed biochemical and behavioural changes. Administration of L-serine until the second postnatal week also normalized brain weight in Slc1a4-E256K mice. Our observations suggest that the transport of 'non-essential' amino acids from the blood through the BBB is at least as important as that of essential amino acids for brain metabolism and development. We propose that SLC1A4 mutations cause a BBB aminoacidopathy with deficits in serine import across the BBB, required for optimal brain growth, leading to a metabolic microcephaly, which may be amenable to treatment with L-serine.

Clinical use of ACQUIRE Therapy for Children Diagnosed With CASK-Gene Related Disabilities

Objective

To report practice based evidence built on clinical findings where an intensive therapeutic approach called ACQUIRE Therapy was used as a rehabilitation/habilitation tool for children diagnosed with CASK mutations. ACQUIRE Therapy delivery is based on principles of learning and guided by a therapeutic framework often used in the delivery of intensive therapy.

Design

Clinical Cohort.

Setting

Natural environments (eg, home-like environment).

Participants

A total of 20 females, 12 to 128 months, mean age = 44.75 (SD = 31.64).

Intervention

Trained Occupational therapists delivered high-dosage rehabilitation for an average of 64.06 hours (SD = 12.91) across 4 weeks. ACQUIRE Therapy targeted cross-domain intervention targets often associated with executive control and praxis.

Main outcome measures

Clinical data was examined from the following sources; therapist daily treatment documentation (eg, therapy goals, video recordings, daily therapy logs, and discharge documentation).

Results

Receptive communication improved in all children. The most common motor skill improvements occurred in trunk control occurring in 33% of children; followed by, gross reaching abilities in 21% of children; fine-motor skills in 19%; head control in 15%; and mobility in 12%. Documentation of cognitive-motor pairing of skills was documented in all children.

Conclusions

Diagnosis specific intervention targets (eg, attention and cognitive-pairing skills) need to be considered when providing therapeutic services to children with CASK-gene mutations and other forms of Global Developmental Delay.Clinicaltrials.gov registration number is NCT03325946. Date of registration: 1 May 2013. Trial Dates: December 2014 and October 2023. https://clinicaltrials.gov/study/NCT03325946?locStr=Roanoke,%20VA&country=United%20States&state=Virginia&city=Roanoke&cond=Cerebral%20Palsy&intr=Intensive%20therapy&rank=2.

Whole-Exome and Transcriptome Sequencing Expands the Genotype of Majewski Osteodysplastic Primordial Dwarfism Type II

Microcephalic Osteodysplastic Primordial Dwarfism type II (MOPDII) represents the most common form of primordial dwarfism. MOPD clinical features include severe prenatal and postnatal growth retardation, postnatal severe microcephaly, hypotonia, and an increased risk for cerebrovascular disease and insulin resistance. Autosomal recessive biallelic loss-of-function genomic variants in the centrosomal pericentrin (PCNT) gene on chromosome 21q22 cause MOPDII. Over the past decade, exome sequencing (ES) and massive RNA sequencing have been effectively employed for both the discovery of novel disease genes and to expand the genotypes of well-known diseases. In this paper we report the results both the RNA sequencing and ES of three patients affected by MOPDII with the aim of exploring whether differentially expressed genes and previously uncharacterized gene variants, in addition to PCNT pathogenic variants, could be associated with the complex phenotype of this disease. We discovered a downregulation of key factors involved in growth, such as IGF1R, IGF2R, and RAF1, in all three investigated patients. Moreover, ES identified a shortlist of genes associated with deleterious, rare variants in MOPDII patients. Our results suggest that Next Generation Sequencing (NGS) technologies can be successfully applied for the molecular characterization of the complex genotypic background of MOPDII.

Diagnostic yield and novel candidate genes for neurodevelopmental disorders by exome sequencing in an unselected cohort with microcephaly

OBJECTIVES

Microcephaly is caused by reduced brain volume and most usually associated with a variety of neurodevelopmental disorders (NDDs). To provide an overview of the diagnostic yield of whole exome sequencing (WES) and promote novel candidates in genetically unsolved families, we studied the clinical and genetic landscape of an unselected Chinese cohort of patients with microcephaly.

METHODS

We performed WES in an unselected cohort of 103 NDDs patients with microcephaly as one of the features. Full evaluation of potential novel candidate genes was applied in genetically undiagnosed families. Functional validations of selected variants were conducted in cultured cells. To augment the discovery of novel candidates, we queried our genomic sequencing data repository for additional likely disease-causing variants in the identified candidate genes.

RESULTS

In 65 families (63.1%), causative sequence variants (SVs) and clinically relevant copy number variants (CNVs) with a pathogenic or likely pathogenic (P/LP) level were identified. By incorporating coverage analysis to WES, a pathogenic or likely pathogenic CNV was detected in 15 families (16/103, 15.5%). In another eight families (8/103, 7.8%), we identified variants in newly reported gene (CCND2) and potential novel neurodevelopmental disorders /microcephaly candidate genes, which involved in cell cycle and division (PWP2, CCND2), CDC42/RAC signaling related actin cytoskeletal organization (DOCK9, RHOF), neurogenesis (ELAVL3, PPP1R9B, KCNH3) and transcription regulation (IRF2BP1). By looking into our data repository of 5066 families with NDDs, we identified additional two cases with variants in DOCK9 and PPP1R9B, respectively.

CONCLUSION

Our results expand the morbid genome of monogenic neurodevelopmental disorders and support the adoption of WES as a first-tier test for individuals with microcephaly.

The role of histone methyltransferases in neurocognitive disorders associated with brain size abnormalities

Brain size is controlled by several factors during neuronal development, including neural progenitor proliferation, neuronal arborization, gliogenesis, cell death, and synaptogenesis. Multiple neurodevelopmental disorders have co-morbid brain size abnormalities, such as microcephaly and macrocephaly. Mutations in histone methyltransferases that modify histone H3 on Lysine 36 and Lysine 4 (H3K36 and H3K4) have been identified in neurodevelopmental disorders involving both microcephaly and macrocephaly. H3K36 and H3K4 methylation are both associated with transcriptional activation and are proposed to sterically hinder the repressive activity of the Polycomb Repressor Complex 2 (PRC2). During neuronal development, tri-methylation of H3K27 (H3K27me3) by PRC2 leads to genome wide transcriptional repression of genes that regulate cell fate transitions and neuronal arborization. Here we provide a review of neurodevelopmental processes and disorders associated with H3K36 and H3K4 histone methyltransferases, with emphasis on processes that contribute to brain size abnormalities. Additionally, we discuss how the counteracting activities of H3K36 and H3K4 modifying enzymes vs. PRC2 could contribute to brain size abnormalities which is an underexplored mechanism in relation to brain size control.

Clinical Reasoning: A Teenage Girl With Progressive Hyperkinetic Movements, Seizures, and Encephalopathy

The "epilepsy-dyskinesia" spectrum is increasingly recognized in neurogenetic and neurometabolic conditions. It can be challenging to diagnose because of clinical and genetic heterogeneity, atypical or nonspecific presentations, and the rarity of each diagnostic entity. This is further complicated by the lack of sensitive or specific biomarkers for most nonenzymatic neurometabolic conditions. Nevertheless, clinical awareness and timely diagnosis are paramount to facilitate appropriate prognostication, counseling, and management.This report describes a case of a teenage girl who had presented at 14 months with a protracted illness manifesting as gastrointestinal upset and associated motor and cognitive regression. A choreoathetoid movement disorder, truncal ataxia, and microcephaly evolved after the acute phase. Neurometabolic and inflammatory investigations, EEG, brain MRI, muscle biopsy (including respiratory chain enzyme studies), and targeted genetic testing were unremarkable. A second distinct regression phase ensued at 14 years consisting of encephalopathy, multifocal motor seizures, absent deep tendon reflexes and worsening movements, gut dysmotility, and dysphagia. Video EEGs showed an evolving developmental and epileptic encephalopathy with multifocal seizures and nonepileptic movements. MRI of the brain revealed evolving and fluctuating patchy bihemispheric cortical changes, cerebellar atrophy with signal change, mild generalized brain volume loss, and abnormal lactate on MR spectroscopy. The article discusses the differential diagnostic approach and management options for patients presenting with neurologic regression, encephalopathy, seizures, and hyperkinetic movements. It also emphasizes the utility of next-generation sequencing in providing a rapid, efficient, cost-effective way of determining the underlying etiology of complex neurologic presentations.

Drugs to limit Zika virus infection and implication for maternal-fetal health

Although the placenta has robust defense mechanisms that protect the fetus from a viral infection, some viruses can manipulate or evade these mechanisms and disrupt physiology or cross the placental barrier. It is well established that the Zika virus is capable of vertical transmission from mother to fetus and can cause malformation of the fetal central nervous system (i.e., microcephaly), as well as Guillain-Barre syndrome in adults. This review seeks to gather and assess the contributions of translational research associated with Zika virus infection, including maternal-fetal vertical transmission of the virus. Nearly 200 inhibitors that have been evaluated in vivo and/or in vitro for their therapeutic properties against the Zika virus are summarized in this review. We also review the status of current vaccine candidates. Our main objective is to provide clinically relevant information that can guide future research directions and strategies for optimized treatment and preventive care of infections caused by Zika virus or similar pathogens.

Pitt-Hopkins syndrome accompanying hypoxic ischemic encephalopathy in a newborn

Hypoxic-ischemic encephalopathy (HIE) is one of the substantial causes of developmental-cognitive disability in neonates. In this early period, it is difficult to diagnose accompanying or predisposing genetic diseases in HIE patients. Herein, we present a patient with HIE who was diagnosed with Pitt-Hopkins syndrome in the newborn period.

Counteracting epigenetic mechanisms regulate the structural development of neuronal circuitry in human neurons

Autism spectrum disorders (ASD) are associated with defects in neuronal connectivity and are highly heritable. Genetic findings suggest that there is an overrepresentation of chromatin regulatory genes among the genes associated with ASD. ASH1 like histone lysine methyltransferase (ASH1L) was identified as a major risk factor for ASD. ASH1L methylates Histone H3 on Lysine 36, which is proposed to result primarily in transcriptional activation. However, how mutations in ASH1L lead to deficits in neuronal connectivity associated with ASD pathogenesis is not known. We report that ASH1L regulates neuronal morphogenesis by counteracting the catalytic activity of Polycomb Repressive complex 2 group (PRC2) in stem cell-derived human neurons. Depletion of ASH1L decreases neurite outgrowth and decreases expression of the gene encoding the neurotrophin receptor TrkB whose signaling pathway is linked to neuronal morphogenesis. The neuronal morphogenesis defect is overcome by inhibition of PRC2 activity, indicating that a balance between the Trithorax group protein ASH1L and PRC2 activity determines neuronal morphology. Thus, our work suggests that ASH1L may epigenetically regulate neuronal morphogenesis by modulating pathways like the BDNF-TrkB signaling pathway. Defects in neuronal morphogenesis could potentially impair the establishment of neuronal connections which could contribute to the neurodevelopmental pathogenesis associated with ASD in patients with ASH1L mutations.

Complete loss of the X-linked gene CASK causes severe cerebellar degeneration

BACKGROUND

Heterozygous loss of X-linked genes like CASK and MeCP2 (Rett syndrome) causes developmental delay in girls, while in boys, loss of the only allele of these genes leads to epileptic encephalopathy. The mechanism for these disorders remains unknown. CASK-linked cerebellar hypoplasia is presumed to result from defects in Tbr1-reelin-mediated neuronal migration.

METHOD

Here we report clinical and histopathological analyses of a deceased 2-month-old boy with a CASK-null mutation. We next generated a mouse line where CASK is completely deleted (hemizygous and homozygous) from postmigratory neurons in the cerebellum.

RESULT

The CASK-null human brain was smaller in size but exhibited normal lamination without defective neuronal differentiation, migration or axonal guidance. The hypoplastic cerebellum instead displayed astrogliosis and microgliosis, which are markers for neuronal loss. We therefore hypothesise that CASK loss-induced cerebellar hypoplasia is the result of early neurodegeneration. Data from the murine model confirmed that in CASK loss, a small cerebellum results from postdevelopmental degeneration of cerebellar granule neurons. Furthermore, at least in the cerebellum, functional loss from CASK deletion is secondary to degeneration of granule cells and not due to an acute molecular functional loss of CASK. Intriguingly, female mice with heterozygous deletion of CASK in the cerebellum do not display neurodegeneration.

CONCLUSION

We suggest that X-linked neurodevelopmental disorders like CASK mutation and Rett syndrome are pathologically neurodegenerative; random X-chromosome inactivation in heterozygous mutant girls, however, results in 50% of cells expressing the functional gene, resulting in a non-progressive pathology, whereas complete loss of the only allele in boys leads to unconstrained degeneration and encephalopathy.

Case Report: Novel SLC9A6 Splicing Variant in a Chinese Boy With Christianson Syndrome With Electrical Status Epilepticus During Sleep

We investigated the existence and potential pathogenicity of a SLC9A6 splicing variant in a Chinese boy with Christianson Syndrome (CS), which was reported for the first time in China. Trio whole-exome sequencing (WES) was performed in the proband and his parents. Multiple computer prediction tools were used to evaluate the pathogenicity of the variant, and reverse transcription-polymerase chain reaction (RT-PCR) analysis and cDNA sequencing were performed to verify the RNA splicing results. The patient presented with characteristic features of CS: global developmental delay, seizures, absent speech, truncal ataxia, microcephaly, ophthalmoplegia, smiling face and hyperkinesis with electrical status epilepticus during sleep (ESES) detected in an electroencephalogram (EEG). A SLC9A6 splicing variant was identified by WES and complete skipping of exon 10 was confirmed by RT-PCR. This resulted in altered gene function and was predicted to be pathogenic. ESES observed early in the disease course is considered to be a significant feature of CS with the SLC9A6 variant. Combined genetic analysis at both the DNA and RNA levels is necessary to confirm the pathogenicity of this variant and its role in the clinical diagnosis of CS.

Exome Sequencing Reveals Novel Variants and Expands the Genetic Landscape for Congenital Microcephaly

Congenital microcephaly causes smaller than average head circumference relative to age, sex and ethnicity and is most usually associated with a variety of neurodevelopmental disorders. The underlying etiology is highly heterogeneous and can be either environmental or genetic. Disruption of any one of multiple biological processes, such as those underlying neurogenesis, cell cycle and division, DNA repair or transcription regulation, can result in microcephaly. This etiological heterogeneity manifests in a clinical variability and presents a major diagnostic and therapeutic challenge, leaving an unacceptably large proportion of over half of microcephaly patients without molecular diagnosis. To elucidate the clinical and genetic landscapes of congenital microcephaly, we sequenced the exomes of 191 clinically diagnosed patients with microcephaly as one of the features. We established a molecular basis for microcephaly in 71 patients (37%), and detected novel variants in five high confidence candidate genes previously unassociated with this condition. We report a large number of patients with mutations in tubulin-related genes in our cohort as well as higher incidence of pathogenic mutations in MCPH genes. Our study expands the phenotypic and genetic landscape of microcephaly, facilitating differential clinical diagnoses for disorders associated with most commonly disrupted genes in our cohort.

MRI of Malformations of Cortical Development- A Comprehensive Review

MCDs (malformations of cortical development) are structural anomalies that disrupt the normal process of the cortical development. These include microcephaly with simplified gyral pattern/microlissencephaly, hemimegalencephaly, focal cortical dysplasia, lissencephaly, heterotopia, polymicrogyria and schizencephaly. They can present with intractable epilepsy, developmental delay, neurological deficits or cognitive impairment. Though the definitive diagnosis of MCD depends on histopathology, the pathological tissue is rarely available hence diagnosis begins with neuroimaging. This article shall briefly review the embryology followed by specific MRI imaging features of MCD in an attempt to simplify the process of diagnosing these disorders with clinical and genetic correlation.A table has been included to highlight the embryological, clinical and genetic findings associated with various MCDs.

FOXR1 regulates stress response pathways and is necessary for proper brain development

The forkhead box (Fox) family of transcription factors are highly conserved and play essential roles in a wide range of cellular and developmental processes. We report an individual with severe neurological symptoms including postnatal microcephaly, progressive brain atrophy and global developmental delay associated with a de novo missense variant (M280L) in the FOXR1 gene. At the protein level, M280L impaired FOXR1 expression and induced a nuclear aggregate phenotype due to protein misfolding and proteolysis. RNAseq and pathway analysis showed that FOXR1 acts as a transcriptional activator and repressor with central roles in heat shock response, chaperone cofactor-dependent protein refolding and cellular response to stress pathways. Indeed, FOXR1 expression is increased in response to cellular stress, a process in which it directly controls HSPA6, HSPA1A and DHRS2 transcripts. The M280L mutant compromises FOXR1's ability to respond to stress, in part due to impaired regulation of downstream target genes that are involved in the stress response pathway. Quantitative PCR of mouse embryo tissues show Foxr1 expression in the embryonic brain. Using CRISPR/Cas9 gene editing, we found that deletion of mouse Foxr1 leads to a severe survival deficit while surviving newborn Foxr1 knockout mice have reduced body weight. Further examination of newborn Foxr1 knockout brains revealed a decrease in cortical thickness and enlarged ventricles compared to littermate wild-type mice, suggesting that loss of Foxr1 leads to atypical brain development. Combined, these results suggest FOXR1 plays a role in cellular stress response pathways and is necessary for normal brain development.

Biallelic truncating variants in ATP9A cause a novel neurodevelopmental disorder involving postnatal microcephaly and failure to thrive

Background

Genes implicated in the Golgi and endosomal trafficking machinery are crucial for brain development, and mutations in them are particularly associated with postnatal microcephaly (POM).

Methods

Exome sequencing was performed in three affected individuals from two unrelated consanguineous families presenting with delayed neurodevelopment, intellectual disability of variable degree, POM and failure to thrive. Patient-derived fibroblasts were tested for functional effects of the variants.

Results

We detected homozygous truncating variants in ATP9A. While the variant in family A is predicted to result in an early premature termination codon, the variant in family B affects a canonical splice site. Both variants lead to a substantial reduction of ATP9A mRNA expression. It has been shown previously that ATP9A localises to early and recycling endosomes, whereas its depletion leads to altered gene expression of components from this compartment. Consistent with previous findings, we also observed overexpression of ARPC3 and SNX3, genes strongly interacting with ATP9A.

Conclusion

In aggregate, our findings show that pathogenic variants in ATP9A cause a novel autosomal recessive neurodevelopmental disorder with POM. While the physiological function of endogenous ATP9A is still largely elusive, our results underline a crucial role of this gene in endosomal transport in brain tissue.

Human-Specific Genes, Cortical Progenitor Cells, and Microcephaly

Over the past few years, human-specific genes have received increasing attention as potential major contributors responsible for the 3-fold difference in brain size between human and chimpanzee. Accordingly, mutations affecting these genes may lead to a reduction in human brain size and therefore, may cause or contribute to microcephaly. In this review, we will concentrate, within the brain, on the cerebral cortex, the seat of our higher cognitive abilities, and focus on the human-specific gene ARHGAP11B and on the gene family comprising the three human-specific genes NOTCH2NLA, -B, and -C. These genes are thought to have significantly contributed to the expansion of the cerebral cortex during human evolution. We will summarize the evolution of these genes, as well as their expression and functional role during human cortical development, and discuss their potential relevance for microcephaly. Furthermore, we will give an overview of other human-specific genes that are expressed during fetal human cortical development. We will discuss the potential involvement of these genes in microcephaly and how these genes could be studied functionally to identify a possible role in microcephaly.

Engineered microRNA-based regulatory element permits safe high-dose miniMECP2 gene therapy in Rett mice

MECP2 gene transfer has been shown to extend the survival of Mecp2-/y knockout (KO) mice modeling Rett syndrome (RTT), an X-linked neurodevelopmental disorder. However, controlling deleterious overexpression of MeCP2 remains the critical unmet obstacle towards a safe and effective gene therapy approach for RTT. A recently developed truncated miniMECP2 gene has also been shown to be therapeutic after AAV9-mediated gene transfer in KO neonates. We show that AAV9/miniMECP2 has a similar dose-dependent toxicity profile to that of a published second-generation AAV9/MECP2 vector after treatment in adolescent mice. To overcome that toxicity, we developed a risk-driven viral genome design strategy rooted in high-throughput profiling and genome mining to rationally develop a compact, synthetic miRNA target panel (miR-Responsive Auto-Regulatory Element, "miRARE") to minimize the possibility of miniMECP2 transgene overexpression in the context of RTT gene therapy. The goal of miRARE is to have a built-in inhibitory element responsive to MeCP2 overexpression. The data provided herein show that insertion of miRARE into the miniMECP2 gene expression cassette greatly improved the safety of miniMECP2 gene transfer without compromising efficacy. Importantly, this built-in regulation system does not require any additional exogenous drug application, and no miRNAs are expressed from the transgene cassette. Although broad applications of miRARE have yet to be determined, the design of miRARE suggests a potential use in gene therapy approaches for other dose-sensitive genes.

The eldest case of MICPCH with CASK mutation exhibiting gross motor regression

BACKGROUND

MICPCH is manifested as microcephaly associated with pontocerebellar hypoplasia and global developmental delay but developmental regression has never been reported. We describe the detailed clinical history of a woman with intellectual disability and microcephaly with pontine and cerebellar hypoplasia (MICPCH) with a CASK mutation who exhibited gross motor regression after adolescence.

CASE

The patient experienced severe motor and intellectual developmental delay with microcephaly from infancy. The initial diagnosis was Rett syndrome based on her clinical features, including hand stereotypes and the absence of structural abnormality on magnetic resonance imaging (MRI) performed at the age of 5 years. Although gross motor abilities developed slowly and she could walk independently, she never acquired speech or understanding of languages. After adolescence, her motor ability gradually regressed so that she was unable to stand without support and moved with a wheelchair. At the age of 31 years, because of her atypical clinical course for Rett syndrome, whole exome sequencing was performed, which revealed a de novo heterozygous c.2068 + 1G > A mutation in the CASK gene (NM_001126055). Brain MRI revealed mild pontocerebellar hypoplasia compatible with the clinical phenotype of MICPCH.

DISCUSSION

This case suggests that MICPCH with a CASK mutation might cause developmental regression after adolescence and might be regarded as a neurodegenerative disorder.

Microcephaly, disproportionate pontine, and cerebellar hypoplasia syndrome: Two novel mutations in the CASK gene were discovered in Chinese females

Microcephaly, disproportionate pontine and cerebellar hypoplasia (MICPCH) syndrome is a rare and genetic disorder, which is mainly caused by mutations in the CASK gene. We described four variations in the CASK gene in Chinese female patients with MICPCH, who presented with microcephaly, developmental delay, and motor disorder. The CASK mutations were identified using NGS (the next-generation sequencing), copy number variation sequencing. Two novel variations in the CASK gene were revealed including a frameshift mutation c.1000_1001insG (p.Asp334GlyfsTer32) and a nonsense mutation c.2110A > T (p.Lys704Ter). Two other aberrations were c.316C > T (p.Arg106Ter) and Xp11.4-p11.3 (41,700,001-44,660,000) × 1 loss. We provided clinical manifestations and neuroimaging findings of the four patients. The genetic variation spectrum of MICPCH caused by CASK was updated. Furthermore, we expounded on the molecular mechanism of the disease and noticed that it was not possible to relate the magnitude of the genetic alteration to a particular phenotype.

Association of term isolated microcephaly with mode of delivery and perinatal outcome - a retrospective case-control analysis

Background

We aimed to evaluate the association of isolated fetal microcephaly measured by ultrasound prior to delivery at term with mode of delivery and perinatal outcome.

Methods

A single-center retrospective study was conducted in 2012–2016. Fetal microcephaly was defined as head circumference > 2 standard deviations of the mean for gestational age and sex. We compared the obstetric, delivery, and outcome parameters of women in whom ultrasound performed up to 10 days prior to term delivery showed isolated fetal microcephaly (study group) or normal head circumference (reference group). Exclusion criteria were intrauterine fetal death, birthweight below the 10th percentile, and antepartum cesarean delivery for any indication.

Results

Of 3677 women included in the study, 26 (0.7%) had a late ultrasound finding of isolated fetal microcephaly. Baseline characteristics were similar in the two groups except for estimated fetal weight based on abdominal circumference and biparietal diameter, which was lower in the microcephaly group (3209.8 ± 557.6 vs. 2685.8 ± 420.8 g, p < .001). There was no significant between-group difference in rate of vaginal operative deliveries (11.7% vs 14.8%, respectively, p = 0.372). The study group had no intrapartum cesarean deliveries compared to 6.3% of the reference group (NS). Compared to controls, neonates in the study group were smaller (3323.2 ± 432.2 vs. 2957.0 ± 330.4 g, p < .001), with lower birthweight percentile (60.5 ± 26.5 vs. 33.6 ± 21.5%, p < .001) and were more often males (48.2 vs. 90.0%, p < .001). No significant differences were noted in perinatal outcomes between the groups, including admission to neonatal intensive care unit, intraventricular hemorrhage, 5-min Apgar score < 7, asphyxia, seizures, and sepsis.

Conclusions

Isolated microcephaly in term fetuses is not advantageous for a vaginal delivery, nor does it does not pose a greater than normal risk of adverse perinatal outcome.

Gene of the month: TLE 1

TLE 1 is the human homologue belonging to a family of four genes and is located on chromosome 9q21. It consists of 19 exons. Although it does not bind directly to DNA, it acts as a repressor of several signalling pathways via transcription factors. TLE1 protein has several physiological roles in embryogenesis, haematopoiesis, general differentiation, and both neuronal and eye development. Much attention was focused on its expression in the tumour cell nuclei of synovial sarcoma (SS). However, several other soft tissue tumours that do and do not share morphological similarity with SS also display nuclear immunoreactivity for TLE1; hence, caution in interpretation is advocated.

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.

The expanding spectrum of movement disorders in genetic epilepsies

An ever-increasing number of neurogenetic conditions presenting with both epilepsy and atypical movements are now recognized. These disorders within the 'genetic epilepsy-dyskinesia' spectrum are clinically and genetically heterogeneous. Increased clinical awareness is therefore necessary for a rational diagnostic approach. Furthermore, careful interpretation of genetic results is key to establishing the correct diagnosis and initiating disease-specific management strategies in a timely fashion. In this review we describe the spectrum of movement disorders associated with genetically determined epilepsies. We also propose diagnostic strategies and putative pathogenic mechanisms causing these complex syndromes associated with both seizures and atypical motor control. WHAT THIS PAPER ADDS: Implicated genes encode proteins with very diverse functions. Pathophysiological mechanisms by which epilepsy and movement disorder phenotypes manifest are often not clear. Early diagnosis of treatable disorders is essential and next generation sequencing may be required.

High-mobility group nucleosomal binding domain 2 protects against microcephaly by maintaining global chromatin accessibility during corticogenesis

The surface area of the human cerebral cortex undergoes dramatic expansion during late fetal development, leading to cortical folding, an evolutionary feature not present in rodents. Microcephaly is a neurodevelopmental disorder defined by an abnormally small brain, and many gene mutations have been found to be associated with primary microcephaly. However, mouse models generated by ablating primary microcephaly-associated genes often fail to recapitulate the severe loss of cortical surface area observed in individuals with this pathology. Here, we show that a mouse model with deficient expression of high-mobility group nucleosomal binding domain 2 (HMGN2) manifests microcephaly with reduced cortical surface area and almost normal radial corticogenesis, with a pattern of incomplete penetrance. We revealed that altered cleavage plane and mitotic delay of ventricular radial glia may explain the rising ratio of intermediate progenitor cells to radial glia and the displacement of neural progenitor cells in microcephalic mutant mice. These led to decreased self-renewal of the radial glia and reduction in lateral expansion. Furthermore, we found that HMGN2 protected corticogenesis by maintaining global chromatin accessibility mainly at promoter regions, thereby ensuring the correct regulation of the transcriptome. Our findings underscore the importance of the regulation of chromatin structure in cortical development and highlight a mouse model with critical insights into the etiology of microcephaly.

Finding Diagnostically Useful Patterns in Quantitative Phenotypic Data

Trio-based whole-exome sequence (WES) data have established confident genetic diagnoses in ∼40% of previously undiagnosed individuals recruited to the Deciphering Developmental Disorders (DDD) study. Here we aim to use the breadth of phenotypic information recorded in DDD to augment diagnosis and disease variant discovery in probands. Median Euclidean distances (mEuD) were employed as a simple measure of similarity of quantitative phenotypic data within sets of ≥10 individuals with plausibly causative de novo mutations (DNM) in 28 different developmental disorder genes. 13/28 (46.4%) showed significant similarity for growth or developmental milestone metrics, 10/28 (35.7%) showed similarity in HPO term usage, and 12/28 (43%) showed no phenotypic similarity. Pairwise comparisons of individuals with high-impact inherited variants to the 32 individuals with causative DNM in ANKRD11 using only growth z-scores highlighted 5 likely causative inherited variants and two unrecognized DNM resulting in an 18% diagnostic uplift for this gene. Using an independent approach, naive Bayes classification of growth and developmental data produced reasonably discriminative models for the 24 DNM genes with sufficiently complete data. An unsupervised naive Bayes classification of 6,993 probands with WES data and sufficient phenotypic information defined 23 in silico syndromes (ISSs) and was used to test a “phenotype first” approach to the discovery of causative genotypes using WES variants strictly filtered on allele frequency, mutation consequence, and evidence of constraint in humans. This highlighted heterozygous de novo nonsynonymous variants in SPTBN2 as causative in three DDD probands.

Elucidation of the phenotypic spectrum and genetic landscape in primary and secondary microcephaly

PURPOSE

Microcephaly is a sign of many genetic conditions but has been rarely systematically evaluated. We therefore comprehensively studied the clinical and genetic landscape of an unselected cohort of patients with microcephaly.

METHODS

We performed clinical assessment, high-resolution chromosomal microarray analysis, exome sequencing, and functional studies in 62 patients (58% with primary microcephaly [PM], 27% with secondary microcephaly [SM], and 15% of unknown onset).

RESULTS

We found severity of developmental delay/intellectual disability correlating with severity of microcephaly in PM, but not SM. We detected causative variants in 48.4% of patients and found divergent inheritance and variant pattern for PM (mainly recessive and likely gene-disrupting [LGD]) versus SM (all dominant de novo and evenly LGD or missense). While centrosome-related pathways were solely identified in PM, transcriptional regulation was the most frequently affected pathway in both SM and PM. Unexpectedly, we found causative variants in different mitochondria-related genes accounting for ~5% of patients, which emphasizes their role even in syndromic PM. Additionally, we delineated novel candidate genes involved in centrosome-related pathway (SPAG5, TEDC1), Wnt signaling (VPS26A, ZNRF3), and RNA trafficking (DDX1).

CONCLUSION

Our findings enable improved evaluation and genetic counseling of PM and SM patients and further elucidate microcephaly pathways.

Mapping causal pathways from genetics to neuropsychiatric disorders using genome-wide imaging genetics: Current status and future directions

Imaging genetics aims to identify genetic variants associated with the structure and function of the human brain. Recently, collaborative consortia have been successful in this goal, identifying and replicating common genetic variants influencing gross human brain structure as measured through magnetic resonance imaging. In this review, we contextualize imaging genetic associations as one important link in understanding the causal chain from genetic variant to increased risk for neuropsychiatric disorders. We provide examples in other fields of how identifying genetic variant associations to disease and multiple phenotypes along the causal chain has revealed a mechanistic understanding of disease risk, with implications for how imaging genetics can be similarly applied. We discuss current findings in the imaging genetics research domain, including that common genetic variants can have a slightly larger effect on brain structure than on risk for disorders like schizophrenia, indicating a somewhat simpler genetic architecture. Also, gross brain structure measurements share a genetic basis with some, but not all, neuropsychiatric disorders, invalidating the previously held belief that they are broad endophenotypes, yet pinpointing brain regions likely involved in the pathology of specific disorders. Finally, we suggest that in order to build a more detailed mechanistic understanding of the effects of genetic variants on the brain, future directions in imaging genetics research will require observations of cellular and synaptic structure in specific brain regions beyond the resolution of magnetic resonance imaging. We expect that integrating genetic associations at biological levels from synapse to sulcus will reveal specific causal pathways impacting risk for neuropsychiatric disorders.

From microcephaly to megalencephaly: determinants of brain size

Expansion of the human brain, and specifically the neocortex, is among the most remarkable evolutionary processes that correlates with cognitive, emotional, and social abilities. Cortical expansion is determined through a tightly orchestrated process of neural stem cell proliferation, migration, and ongoing organization, synaptogenesis, and apoptosis. Perturbations of each of these intricate steps can lead to abnormalities of brain size in humans, whether small (microcephaly) or large (megalencephaly). Abnormalities of brain growth can be clinically isolated or occur as part of complex syndromes associated with other neurodevelopmental problems (eg, epilepsy, autism, intellectual disability), brain malformations, and body growth abnormalities. Thorough review of the genetic literature reveals that human microcephaly and megalencephaly are caused by mutations of a rapidly growing number of genes linked within critical cellular pathways that impact early brain development, with important pathomechanistic links to cancer, body growth, and epilepsy. Given the rapid rate of causal gene identification for microcephaly and megalencephaly understanding the roles and interplay of these important signaling pathways is crucial to further unravel the mechanisms underlying brain growth disorders and, more fundamentally, normal brain growth and development in humans. In this review, we will (a) overview the definitions of microcephaly and megalencephaly, highlighting their classifications in clinical practice; (b) overview the most common genes and pathways underlying microcephaly and megalencephaly based on the fundamental cellular processes that are perturbed during cortical development; and (c) outline general clinical molecular diagnostic workflows for children and adults presenting with microcephaly and megalencephaly.

Delineating FOXG1 syndrome: From congenital microcephaly to hyperkinetic encephalopathy

Objective

To provide new insights into the FOXG1-related clinical and imaging phenotypes and refine the phenotype-genotype correlation in FOXG1 syndrome.

Methods

We analyzed the clinical and imaging phenotypes of a cohort of 45 patients with a pathogenic or likely pathogenic FOXG1 variant and performed phenotype-genotype correlations.

Results

A total of 37 FOXG1 different heterozygous mutations were identified, of which 18 are novel. We described a broad spectrum of neurodevelopmental phenotypes, characterized by severe postnatal microcephaly and developmental delay accompanied by a hyperkinetic movement disorder, stereotypes and sleep disorders, and epileptic seizures. Our data highlighted 3 patterns of gyration, including frontal pachygyria in younger patients (26.7%), moderate simplified gyration (24.4%) and mildly simplified or normal gyration (48.9%), corpus callosum hypogenesis mostly in its frontal part, combined with moderate-to-severe myelination delay that improved and normalized with age. Frameshift and nonsense mutations in the N-terminus of FOXG1, which are the most common mutation types, show the most severe clinical features and MRI anomalies. However, patients with recurrent frameshift mutations c.460dupG and c.256dupC had variable clinical and imaging presentations.

Conclusions

These findings have implications for genetic counseling, providing evidence that N-terminal mutations and large deletions lead to more severe FOXG1 syndrome, although genotype-phenotype correlations are not necessarily straightforward in recurrent mutations. Together, these analyses support the view that FOXG1 syndrome is a specific disorder characterized by frontal pachygyria and delayed myelination in its most severe form and hypogenetic corpus callosum in its milder form.

Diagnostic approach to fetal microcephaly

Microcephaly in utero is conventionally defined as a fetal head circumference (HC) 3SD below the mean for gestational age according to Jeanty et al.'s reference range. Prediction of microcephaly at birth (micB) based on conventional prenatal biometry is associated with a high percentage of false positive diagnoses and as a result, in countries in which it is an option, termination of pregnancy may be offered in cases that would have culminated in birth of a normocephalic child. A false negative diagnosis is rarer, but may lead to the birth of a symptomatic microcephalic child. In this review we present the results of our recent studies aimed at improvement of accurate prenatal detection of microcephaly including: (1), application of two new reference ranges for fetal HC in cases with a prenatal diagnosis of microcephaly based on the conventional reference; (2) assessment whether integration of additional parameters (stricter fetal HC cut-offs, small-for-gestational age (SGA), decreased HC/abdominal circumference and HC/femur length ratios, presence of associated malformations and family history) can improve prediction; (3), estimation of the difference between Z-scores of prenatal HC and the corresponding occipitofrontal circumference (OFC) at birth in order to propose an adjustment for better prediction of the actual OFC deviation at birth; (4), assessment whether micB diagnosis can be improved by accurate detection of false positive Fmic cases whose small HC is due to an acrocephalic-like head deformation by applying a new reference range of a vertical measurement of the fetal head: foramen magnum-to-cranium distance (FCD). The conventional and new reference ranges for fetal HC, all result in considerable over-diagnosis of fetal microcephaly (ranging from 43% to 33%). The use of the new references does not significantly improve micB prediction compared with the conventional one, whilst integrating additional parameters results in a better positive predictive value (PPV), but an increase in false negatives. The degree of Fmic severity is significantly over-estimated compared to the corresponding micB. The difference between the postnatal OFC deviation from the mean and the prenatal HC ranges from -0.74 SD to -1.95 SD for various fetal HC references. Application of the reference range for vertical cranial dimensions enables exclusion of fetuses with a small HC associated with a vertical cranial deformity without missing those with actual micB. Combining the fetal HC with the developed FCD criteria raised the PPV of micB to 78%. CONCLUSIONS: Prediction of micB can be improved by integrating additional parameters and by application of the FCD criteria, however the correct diagnosis of Fmic remains challenging. An algorithm for evaluation of fetal microcephaly is provided.

Genetic Diagnostics for Neurologists

PURPOSE OF REVIEW

This article puts advances in the field of neurogenetics into context and provides a quick review of the broad concepts necessary for current practice in neurology.

RECENT FINDINGS

The exponential growth of genetic testing is due to its increased speed and decreasing cost, and it is now a routine part of the clinical care for a number of neurologic patients. In addition, phenotypic pleiotropy (mutations in the same gene causing very disparate phenotypes) and genetic heterogeneity (the same clinical phenotype resulting from mutations in different genes) are now known to exist in a number of conditions, adding an additional layer of complexity for genetic testing in these disorders.

SUMMARY

Although the growing complexity of technical knowledge in the ordering and interpretation of genetic tests makes it necessary for neurologists to consult medical geneticists, limitations in the availability of such professionals often means neurologists will be on the front line dealing with suspected or confirmed neurogenetic conditions. The growing availability of broad genetic testing through chromosomal microarray and next-generation sequencing and the expanded phenotypic spectrum of many conditions has implications for genetic counseling and medical management. This article discusses the various forms of genetic variability and how to test for each of them. It also provides an update on the most common forms of neurologic presentations of genetic disease and a review of testing strategies.

Counter-Balance Between Gli3 and miR-7 Is Required for Proper Morphogenesis and Size Control of the Mouse Brain

Brain morphogenesis requires precise regulation of multiple genes to control specification of distinct neural progenitors (NPs) and neuronal production. Dysregulation of these genes results in severe brain malformation such as macrocephaly and microcephaly. Despite studies of the effect of individual pathogenic genes, the counter-balance between multiple factors in controlling brain size remains unclear. Here we show that cortical deletion of Gli3 results in enlarged brain and folding structures in the cortical midline at the postnatal stage, which is mainly caused by the increased percentage of intermediate progenitors (IPs) and newborn neurons. In addition, dysregulation of neuronal migration also contributes to the folding defects in the cortical midline region. Knockdown of microRNA (miRNA) miR-7 can rescue abnormal brain morphology in Gli3 knockout mice by recovering progenitor specification, neuronal production and migration through a counter-balance of the Gli3 activity. Moreover, miR-7 likely exerts its function through silencing target gene Pax6. Our results indicate that proper brain morphogenesis is an outcome of interactive regulations of multiple molecules such as Gli3 and miR-7. Because miRNAs are easy to synthesize and deliver, miR-7 could be a potential therapeutic means to macrocephaly caused by Gli3-deficiency.

Pitt-Hopkins Syndrome: A Review of Current Literature, Clinical Approach, and 23-Patient Case Series

Pitt-Hopkins syndrome (PTHS) is a rare, genetic disorder caused by a molecular variant of TCF4 which is involved in embryologic neuronal differentiation. PTHS is characterized by syndromic facies, psychomotor delay, and intellectual disability. Other associated features include early-onset myopia, seizures, constipation, and hyperventilation-apneic spells. Many also meet criteria for autism spectrum disorder. Here the authors present a series of 23 PTHS patients with molecularly confirmed TCF4 variants and describe 3 unique individuals. The first carries a small deletion but does not exhibit the typical facial features nor the typical pattern of developmental delay. The second exhibits typical facial features, but has attained more advanced motor and verbal skills than other reported cases to date. The third displays typical features of PTHS, however inherited a large chromosomal duplication involving TCF4 from his unaffected father with somatic mosaicism. To the authors' knowledge, this is the first chromosomal duplication case reported to date.

Congenital microcephaly: A diagnostic challenge during Zika epidemics

The multiple, wide and diverse etiologies of congenital microcephaly are complex and multifactorial. Recent advances in genetic testing have improved understanding of novel genetic causes of congenital microcephaly. The recent Zika virus (ZIKV) epidemic in Latin America has highlighted the need for a better understanding of the underlying pathological mechanisms of microcephaly including both infectious and non-infectious causes. The diagnostic approach to microcephaly needs to include potential infectious and genetic etiologies, as well as environmental in-utero exposures such as alcohol, toxins, and medications. Emerging genetic alterations linked to microcephaly include abnormal mitotic microtubule spindle structure and abnormal function of centrosomes. We discuss the diagnostic challenge of congenital microcephaly in the context of understanding the links with ZIKV emergence as a new etiological factor involved in this birth defect.

Genetic control of postnatal human brain growth

PURPOSE OF REVIEW

Studies investigating postnatal brain growth disorders inform the biology underlying the development of human brain circuitry. This research is becoming increasingly important for the diagnosis and treatment of childhood neurodevelopmental disorders, including autism and related disorders. Here, we review recent research on typical and abnormal postnatal brain growth and examine potential biological mechanisms.

RECENT FINDINGS

Clinically, brain growth disorders are heralded by diverging head size for a given age and sex, but are more precisely characterized by brain imaging, post-mortem analysis, and animal model studies. Recent neuroimaging and molecular biological studies on postnatal brain growth disorders have broadened our view of both typical and pathological postnatal neurodevelopment. Correlating gene and protein function with brain growth trajectories uncovers postnatal biological mechanisms, including neuronal arborization, synaptogenesis and pruning, and gliogenesis and myelination. Recent investigations of childhood neurodevelopmental and neurodegenerative disorders highlight the underlying genetic programming and experience-dependent remodeling of neural circuitry.

SUMMARY

To understand typical and abnormal postnatal brain development, clinicians and researchers should characterize brain growth trajectories in the context of neurogenetic syndromes. Understanding mechanisms and trajectories of postnatal brain growth will aid in differentiating, diagnosing, and potentially treating neurodevelopmental disorders.

Prenatal imaging findings in fetal Zika virus infection

PURPOSE OF REVIEW

The aim of this review is to report the most recent observations concerning intrauterine Zika virus (ZIKV) infection and associated neuroimaging.

RECENT FINDINGS

ZIKV outbreak in Brazil in 2015 was associated with an impressive registration of cases of congenital microcephaly in women with symptoms suggestive of ZIKV infection. Clinical and laboratory testing for ZIKV and hypothetic etiopathogenetic mechanisms are described. Diagnostic tests on blood, urine and amniotic fluid should be performed in all mothers with symptoms suggestive of intrauterine ZIKV infection. ZIKV causes multiple teratogenic malformations, mainly affecting the developing brain.

SUMMARY

Neuroimaging investigation contributes to the prenatal detection of microcephaly and other brain abnormalities in cases of intrauterine ZIKV infection. Neuroimaging is based antenatally on two-dimensional and three-dimensional ultrasound and fetal MRI, whereas computed tomography scan is performed postnatally. Although neuropathology associated with intrauterine ZIKV infection is characterized by nonspecific findings of brain disorder, reduced cortical gyration and white-matter hypomyelination or dysmyelination and cerebellar hypoplasia have been consistently observed in the majority of fetuses and newborns. Prenatal or postnatal genetic workup should be carried out to exclude cases of primary microcephaly. Follow-up should rely upon MRI and computed tomography scan as well as neuropediatrician to better define developmental outcome in survivors.

A clinical series using intensive neurorehabilitation to promote functional motor and cognitive skills in three girls with CASK mutation

Objectives

Children with microcephaly face lifelong psychomotor, cognitive, and communications skills disabilities. Etiology of microcephaly is heterogeneous but presentation often includes seizures, hypotonia, ataxia, stereotypic movements, attention deficits, excitability, cognitive delays, and poor communication skills. Molecular diagnostics have outpaced available interventions and most children receive generic physical, speech, and occupational therapies with little attention to the efficacy of such treatments. Mutations in the X-linked intellectual disability gene (XLID) CASK is one etiology associated with microcephaly which produces mental retardation and microcephaly with pontine and cerebellar hypoplasia (MICPCH; OMIM# 300749). We pilot-tested an intensive therapy in three girls with heterozygous mutation in the gene CASK and MICPCH. Child A = 54 months; Child B = 89 months; and Child C = 24 months received a targeted treatment to improve gross/fine motor skills, visual-motor coordination, social interaction, and communication. Treatment was 4 h each weekday for 10 treatment days. Operant training promoted/refined goal-directed activities. The Peabody Developmental Motor Scales 2 was administered pre- and post-treatment.

Results

Child A gained 14 developmental months; Child B gained 20 developmental months; and Child C gained 39 developmental months. This case series suggests that children with MICPCH are responsive to intensive therapy aimed at increasing functional skills/independence.

Trial Registration ClinicalTrials.gov Registration Number: NCT03325946; Release Date: October 30, 2017

Haploinsufficiency of the Chromatin Remodeler BPTF Causes Syndromic Developmental and Speech Delay, Postnatal Microcephaly, and Dysmorphic Features

Bromodomain PHD finger transcription factor (BPTF) is the largest subunit of nucleosome remodeling factor (NURF), a member of the ISWI chromatin-remodeling complex. However, the clinical consequences of disruption of this complex remain largely uncharacterized. BPTF is required for anterior-posterior axis formation of the mouse embryo and was shown to promote posterior neuroectodermal fate by enhancing Smad2-activated wnt8 expression in zebrafish. Here, we report eight loss-of-function and two missense variants (eight de novo and two of unknown origin) in BPTF on 17q24.2. The BPTF variants were found in unrelated individuals aged between 2.1 and 13 years, who manifest variable degrees of developmental delay/intellectual disability (10/10), speech delay (10/10), postnatal microcephaly (7/9), and dysmorphic features (9/10). Using CRISPR-Cas9 genome editing of bptf in zebrafish to induce a loss of gene function, we observed a significant reduction in head size of F0 mutants compared to control larvae. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and phospho-histone H3 (PH3) staining to assess apoptosis and cell proliferation, respectively, showed a significant increase in cell death in F0 mutants compared to controls. Additionally, we observed a substantial increase of the ceratohyal angle of the craniofacial skeleton in bptf F0 mutants, indicating abnormal craniofacial patterning. Taken together, our data demonstrate the pathogenic role of BPTF haploinsufficiency in syndromic neurodevelopmental anomalies and extend the clinical spectrum of human disorders caused by ablation of chromatin remodeling complexes.

Application of high-resolution array comparative genomic hybridization in children with unknown syndromic microcephaly

BackroundMicrocephaly can either be isolated or it may coexist with other neurological entities and/or multiple congenital anomalies, known as syndromic microcephaly. Although many syndromic cases can be classified based on the characteristic phenotype, some others remain uncertain and require further investigation. The present study describes the application of array-comparative genomic hybridization (array-CGH) as a diagnostic tool for the study of patients with clinically unknown syndromic microcephaly.MethodsFrom a cohort of 210 unrelated patients referred with syndromic microcephaly, we applied array-CGH analysis in 53 undiagnosed cases. In all the 53 cases except one, previous standard karyotype was negative. High-resolution 4 × 180K and 1 × 244K Agilent arrays were used in this study.ResultsIn 25 out of the 53 patients with microcephaly among other phenotypic anomalies, array-CGH revealed copy number variations (CNVs) ranging in size between 15 kb and 31.6 Mb. The identified CNVs were definitely causal for microcephaly in 11/53, probably causal in 7/53, and not causal for microcephaly in 7/53 patients. Genes potentially contributing to brain deficit were revealed in 16/53 patients.ConclusionsArray-CGH contributes to the elucidation of undefined syndromic microcephalic cases by permitting the discovery of novel microdeletions and/or microduplications. It also allows a more precise genotype-phenotype correlation by the accurate definition of the breakpoints in the deleted/duplicated regions.

Microcephaly and Zika virus: Neuroradiological aspects, clinical findings and a proposed framework for early evaluation of child development

BACKGROUND AND AIMS

As the recent outbreak of microcephaly cases caused by Zika virus has been declared a global health emergency, providing assessment guidelines for multidisciplinary teams providing early developmental screening and stimulation to infants with microcephaly is much needed. Thus, the aim of this manuscript is to provide an overview on what is known about neuroradiological aspects and clinical findings in infants with microcephaly caused by Zika virus and to propose a framework for early evaluation of child development.

METHODS

The keywords "Zika virus" and "microcephaly" were searched in PubMed database for articles published from incept to May 2017. These texts were reviewed, and the ones addressing neuroradiological and clinical findings in infants were selected. Recommendations for early assessment were made based on the International Classification of Functionality Disability and Health (ICF) model.

OUTCOMES AND RESULTS

The database search yielded 599 publications and 36 were selected. The studies detected microcephaly with diffuse brain malformations and calcifications, ventriculomegaly, optic nerve hypoplasia, macular atrophy, cataracts, impaired visual and hearing function, arthrogryposis, spasticity, hyperreflexia, irritability, tremors, and seizures, but very little is known about early development. Early assessments were described based on the ICF domains (Body Function and Structures, Activities and Participation and Contextual factors).

CONCLUSION AND IMPLICATIONS

Studies published showed abnormal brain, optic, neurologic and orthopedic findings, but very little is known about other aspects of functioning in infants with microcephaly caused by Zika virus. The biopsychosocial model based on the ICF paradigm provides an adequate framework to describe the condition of the infant with microcephaly receiving rehabilitative efforts to minimize disability. Efforts towards early identification of developmental delays should be taken within the first six months of life.

Chromosomal contacts connect loci associated with autism, BMI and head circumference phenotypes

Copy number variants (CNVs) are major contributors to genomic imbalance disorders. Phenotyping of 137 unrelated deletion and reciprocal duplication carriers of the distal 16p11.2 220 kb BP2-BP3 interval showed that these rearrangements are associated with autism spectrum disorders and mirror phenotypes of obesity/underweight and macrocephaly/microcephaly. Such phenotypes were previously associated with rearrangements of the non-overlapping proximal 16p11.2 600 kb BP4-BP5 interval. These two CNV-prone regions at 16p11.2 are reciprocally engaged in complex chromatin looping, as successfully confirmed by 4C-seq, fluorescence in situ hybridization and Hi-C, as well as coordinated expression and regulation of encompassed genes. We observed that genes differentially expressed in 16p11.2 BP4-BP5 CNV carriers are concomitantly modified in their chromatin interactions, suggesting that disruption of chromatin interplays could participate in the observed phenotypes. We also identified cis- and trans-acting chromatin contacts to other genomic regions previously associated with analogous phenotypes. For example, we uncovered that individuals with reciprocal rearrangements of the trans-contacted 2p15 locus similarly display mirror phenotypes on head circumference and weight. Our results indicate that chromosomal contacts' maps could uncover functionally and clinically related genes.

Further Clinical Delineation of the MEF2C Haploinsufficiency Syndrome: Report on New Cases and Literature Review of Severe Neurodevelopmental Disorders Presenting with Seizures, Absent Speech, and Involuntary Movements

Mutations in the MEF2C ( myocyte enhancer factor 2 ) gene have been established as a cause for an intellectual disability syndrome presenting with seizures, absence of speech, stereotypic movements, hypotonia, and limited ambulation. Phenotypic overlap with Rett's and Angelman's syndromes has been noted. Following the first reports of 5q14.3q15 microdeletions encompassing the MEF2C gene, further cases with point mutations and partial gene deletions of the MEF2C gene have been described. We present the clinical phenotype of our cohort of six patients with MEF2C mutations and compare our findings with previously reported patients as well as with a growing number of genetic conditions presenting with a severe neurodevelopmental, Rett-like, phenotype. We aim to add to the current knowledge of the natural history of the "MEF2C haploinsufficiency syndrome" as well as of the differential diagnosis, clinical management, and genetic counseling in this diagnostically challenging group of patients.

Infantile neurodegenerative disorder associated with mutations in TBCD, an essential gene in the tubulin heterodimer assembly pathway

Mutation in a growing spectrum of genes is known to either cause or contribute to primary or secondary microcephaly. In primary microcephaly the genetic determinants frequently involve mutations that contribute to or modulate the microtubule cytoskeleton by causing perturbations of neuronal proliferation and migration. Here we describe four patients from two unrelated families each with an infantile neurodegenerative disorder characterized by loss of developmental milestones at 9–24 months of age followed by seizures, dystonia and acquired microcephaly. The patients harboured homozygous missense mutations (A475T and A586V) in TBCD, a gene encoding one of five tubulin-specific chaperones (termed TBCA-E) that function in concert as a nanomachine required for the de novo assembly of the α/β tubulin heterodimer. The latter is the subunit from which microtubule polymers are assembled. We found a reduced intracellular abundance of TBCD in patient fibroblasts to about 10% (in the case of A475T) or 40% (in the case of A586V) compared to age-matched wild type controls. Functional analyses of the mutant proteins revealed a partially compromised ability to participate in the heterodimer assembly pathway. We show via in utero shRNA-mediated suppression that a balanced supply of tbcd is critical for cortical cell proliferation and radial migration in the developing mouse brain. We conclude that TBCD is a novel functional contributor to the mammalian cerebral cortex development, and that the pathological mechanism resulting from the mutations we describe is likely to involve compromised interactions with one or more TBCD-interacting effectors that influence the dynamics and behaviour of the neuronal cytoskeleton.