Folic acid and autism: updated evidences.

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition that impairs communication, socialization, and behavior. The association of ASD with folic acid has been investigated due to the importance of this vitamin for neurological health. This study is an update of the publication 'Folic acid and autism: What do we know?' and aims to systematically review studies examining the relationship between folic acid and ASD. The search resulted in 2,389 studies on folic acid and ASD, which were selected by two reviewers based on their titles and abstracts. Studies meeting the inclusion criteria were fully read. The 52 included studies involved 10,429 individuals diagnosed with ASD and assessed the intake of vitamin B6, folic acid, and vitamin B12; serum levels of these vitamins, homocysteine, and methionine; therapeutic interventions using folic acid; and the association between maternal exposure to this vitamin and the risk of ASD. The evidence of insufficient folic acid intake in most individuals with ASD remains consistent in this update. No association was found between maternal exposure to folic acid and the risk of ASD in their children. Despite observed improvements in communication, socialization, and behavior in individuals with ASD following folic acid interventions, it is crucial to consider the individuality and complexity of ASD. Given the relevance of the topic, there remains a need for more high-quality research and clinical trials characterized by rigorous methodological designs.

Association of germinal matrix hemorrhage volume with neurodevelopment and hydrocephalus.

OBJECTIVE: The objective of this study was to evaluate whether volumetric measurements on early cranial ultrasound (CUS) in high-grade germinal matrix hemorrhage-intraventricular hemorrhage (GMH-IVH) are associated with hydrocephalus and neurodevelopmental metrics. METHODS: A retrospective case series analysis of infants with high-grade GMH-IVH admitted to the St. Louis Children's Hospital neonatal intensive care unit between 2007 and 2015 who underwent neurodevelopmental testing using the Bayley Scales of Infant and Toddler Development, 3rd Edition (Bayley-III) at 2 years of corrected age was performed. GMH volume, periventricular hemorrhagic infarction volume, and frontotemporal horn ratio were obtained from direct review of neonatal CUS studies. Univariate and multivariable regression models were used to evaluate the association between hemorrhage volumes and hydrocephalus requiring permanent CSF diversion with ventricular shunt or endoscopic third ventriculostomy with or without choroid plexus cauterization and composite Bayley-III cognitive, language, and motor scores. RESULTS: Forty-three infants (29 males, mean gestational age 25 weeks) met the inclusion criteria. The mean age at time of the CUS with the largest hemorrhage volume or first diagnosis of highest grade was 6.2 days. Nineteen patients underwent treatment for hydrocephalus with permanent CSF diversion. In multivariable analyses, larger GMH volume was associated with worse estimated Bayley-III cognitive (left-sided GMH volume: p = 0.048, total GMH volume: p = 0.023) and motor (left-sided GMH volume: p = 0.010; total GMH volume: p = 0.014) scores. Larger periventricular hemorrhagic infarction volume was associated with worse estimated Bayley-III motor scores (each side p < 0.04). Larger left-sided (OR 2.55, 95% CI 1.10-5.88; p = 0.028) and total (OR 1.35, 95% CI 1.01-1.79; p = 0.041) GMH volumes correlated with hydrocephalus. There was no relationship between early ventricular volume and hydrocephalus or neurodevelopmental outcomes. CONCLUSIONS: Location-specific hemorrhage volume on early CUS may be prognostic for neurodevelopmental and hydrocephalus outcomes in high-grade GMH-IVH.

Sensitivity and specificity of the Neonatal Visual Assessment to predict motor and cognitive outcomes in infants born very preterm.

BACKGROUND: Very preterm infants are at increased risk of neurodevelopmental impairments. The Neonatal Visual Assessment (NVA) assesses visual function and outcomes and has been used to assess early neurodevelopmental outcomes. This study aimed to compare NVA results of very preterm and term-born infants and to calculate the sensitivity and specificity of the NVA at term equivalent age (TEA) and three months corrected age (CA) to predict motor and cognitive outcomes at 12 months CA in very preterm infants. METHODS: This prospective observational cohort study recruited infants born before 31 weeks gestation and a healthy term-born control group. The NVA was assessed at TEA and three months CA, and neurodevelopmental outcomes (Bayley Scales of Infant and Toddler Development, Third Edition; Neurosensory Motor Developmental Assessment; Alberta Infant Motor Scale) were performed at 12 months CA. The sensitivity and specificity of the NVA to predict outcomes were calculated based on a previously published optimality score. RESULTS: 248 preterm (54 % male) and 46 term-born infants (48 % male) were analysed. The mean NVA scores of preterm and term-born infants were significantly different at TEA (preterm 3.1±2.1; term-born 1.2±1.7, p < 0.001). The NVA had moderate sensitivity (59-78 %) and low specificity (25-27 %) at TEA, and low sensitivity (21-28 %) and high specificity (86-87 %) at three months CA for the prediction of preterm infants' outcomes at 12 months CA. CONCLUSION: The NVA at TEA and three months CA was not a strong predictor of motor and cognitive impairments in this contemporary cohort of very preterm infants.

Perinatal influences on academic achievement and the developing brain: a scoping systematic review.

Introduction and methods: In this PRISMA-compliant systematic review, we identify and synthesize the findings of research in which neuroimaging and assessments of achievement have been used to examine the relationships among aspects of developmental programming, neurodevelopment, and achievement in reading and mathematics. Results: Forty-seven studies met inclusion criteria. The majority examined the impact of prematurity (n = 32) and prenatal alcohol exposure (n = 13). Several prematurity studies reported a positive correlation between white-matter integrity of callosal fibers and executive functioning and/or achievement, and white matter properties were consistently associated with cognitive and academic performance in preterm and full-term children. Volumetric studies reported positive associations between academic and cognitive abilities and white and gray matter volume in regions such as the insula, putamen, and prefrontal lobes. Functional MRI studies demonstrated increased right-hemispheric language processing among preterm children. Altered activation of the frontoparietal network related to numerical abilities was also reported. Prenatal alcohol exposure studies reported alterations in white matter microstructure linked to deficits in cognitive functioning and academic achievement, including mathematics, reading, and vocabulary skills. Volumetric studies reported reductions in cerebral, cerebellar, and subcortical gray matter volumes associated with decreased scores on measures of executive functioning, attention, working memory, and academic performance. Functional MRI studies demonstrated broad, diffuse activation, reduced activation in canonical regions, and increased activation in non-canonical regions during numeric tasks. Discussion: A preponderance of studies linked prematurity and prenatal alcohol exposure to altered neurodevelopmental processes and suboptimal academic achievement. Limitations and recommendations for future research are discussed. Systematic review registration: Identifier: DOI 10.17605/OSF.IO/ZAN67.

Green spaces and respiratory, cardiometabolic, and neurodevelopmental outcomes: An individual-participant data meta-analysis of >35.000 European children.

Studies evaluating the benefits and risks of green spaces on children's health are scarce. The present study aimed to examine the associations between exposure to green spaces during pregnancy and early childhood with respiratory, cardiometabolic, and neurodevelopmental outcomes in school-age children. We performed an Individual-Participant Data (IPD) meta-analysis involving 35,000 children from ten European birth cohorts across eight countries. For each participant, we calculated residential Normalized Difference Vegetation Index (NDVI) within a 300 m buffer and the linear distance to green spaces (meters) during prenatal life and childhood. Multiple harmonized health outcomes were selected: asthma and wheezing, lung function, body mass index, diastolic and systolic blood pressure, non-verbal intelligence, internalizing and externalizing problems, and ADHD symptoms. We conducted a two-stage IPD meta-analysis and evaluated effect modification by socioeconomic status (SES) and sex. Between-study heterogeneity was assessed via random-effects meta-regression. Residential surrounding green spaces in childhood, not pregnancy, was associated with improved lung function, particularly higher FEV1 (ß = 0.06; 95 %CI: 0.03, 0.09 I2 = 4.03 %, p < 0.001) and FVC (ß = 0.07; 95 %CI: 0.04, 0.09 I2 = 0 %, p < 0.001) with a stronger association observed in females (p < 0.001). This association remained robust after multiple testing correction and did not change notably after adjusting for ambient air pollution. Increased distance to green spaces showed an association with lower FVC (ß = -0.04; 95 %CI: -0.07, -0.02, I2 = 4.8, p = 0.001), with a stronger effect in children from higher SES backgrounds (p < 0.001). No consistent associations were found between green spaces and asthma, wheezing, cardiometabolic, or neurodevelopmental outcomes, with direction of effect varying across cohorts. Wheezing and neurodevelopmental outcomes showed high between-study heterogeneity, and the age at outcome assessment was only associated with heterogeneity in internalizing problems.. This large European meta-analysis suggests that childhood exposure to green spaces may lead to better lung function. Associations with other respiratory outcomes and selected cardiometabolic and neurodevelopmental outcomes remain inconclusive.

The influence of maternal and paternal parenting on adolescent brain structure.

BACKGROUND: Adolescents raised in families with different maternal and paternal parenting combinations exhibit variations in neurocognition and psychopathology; however, whether neural differences exist remains unexplored. This study used a longitudinal twin sample to delineate how different parenting combinations influence adolescent brain structure and to elucidate the genetic contribution. METHODS: A cohort of 216 twins participated in parenting assessments during early adolescence and underwent MRI scanning during middle adolescence. We utilized latent profile analysis to distinguish between various maternal and paternal parenting profiles and subsequently investigated their influences on brain anatomy. Biometric analysis was applied to assess the genetic influences on brain structure, and associations with internalizing symptoms were explored. RESULTS: In early adolescence, four parenting profiles emerged characterized by levels of harshness and hostility in one or both parents. Compared to adolescents in "catparent" families (low harshness/hostility in both parents), those raised in "tigermom" families (harsh/hostile mother only) exhibited smaller nucleus accumbens volume and larger temporal cortex surface area; those in "tigerdad" families demonstrated larger thalamus volumes; those in "tigerparent" families displayed smaller volumes in the mid-anterior corpus callosum. Genetic risk factors contributed significantly to the observed brain structural heterogeneity and internalizing symptoms. However, the influences of parenting profiles and brain structure on internalizing symptoms were not significant. CONCLUSIONS: The findings underscore distinct brain structural features linked to maternal and paternal parenting combinations, particularly in terms of subcortical volume and cortical surface area. This study suggests an interdependent role of maternal and paternal parenting in shaping adolescent neurodevelopment.

Face-brain correlates as potential sex-specific biomarkers for schizophrenia and bipolar disorder.

Given the shared ectodermal origin and integrated development of the face and the brain, facial biomarkers emerge as potential candidates to assess vulnerability for disorders in which neurodevelopment is compromised, such as schizophrenia (SZ) and bipolar disorder (BD). The sample comprised 188 individuals (67 SZ patients, 46 BD patients and 75 healthy controls (HC)). Using a landmark-based approach on 3D facial reconstructions, we quantified global and local facial shape differences between SZ/BD patients and HC using geometric morphometrics. We also assessed correlations between facial and brain cortical measures. All analyses were performed separately by sex. Diagnosis explained 4.1 % - 5.9 % of global facial shape variance in males and females with SZ, and 4.5 % - 4.1 % in BD. Regarding local facial shape, we detected 43.2 % of significantly different distances in males and 47.4 % in females with SZ as compared to HC, whereas in BD the percentages decreased to 35.8 % and 26.8 %, respectively. We detected that brain area and volume significantly explained 2.2 % and 2 % of facial shape variance in the male SZ - HC sample. Our results support facial shape as a neurodevelopmental marker for SZ and BD and reveal sex-specific pathophysiological mechanisms modulating the interplay between the brain and the face.

Analyzing the Psychometric Properties of Infant (0-24 Months) Developmental Assessments: A Scoping Review.

PURPOSE: To assess the psychometric properties of available developmental assessments for infants, aged 0-24 months. METHODS: A scoping review was conducted using the PRISMA Extension for Scoping Reviews as a guideline. The following four databases: Medline, CINAHL, Embase, and Web of Science were used to retrieve articles. Assessments were analyzed for psychometric properties of reliability and validity. Results: Fifteen developmental assessments were identified and evaluated based on their psychometric properties from 20 number of articles. RESULTS: Three assessments including Bayley Scales of Infant and Toddler Development 3rd Edition (BSID-III), Caregiver Reported Early Development Instruments (CREDI), and Ages and Stages Questionnaire 3rd Edition (ASQ-3), were identified to have the most supporting evidence. CONCLUSION: This study provided clinicians with an updated list of all-encompassing infant developmental assessments. Certain assessments require additional evidence regarding their psychometric properties to substantiate their clinical utility.

Emergence of the ZNF675 Gene During Primate Evolution-Influenced Human Neurodevelopment Through Changing HES1 Autoregulation.

In this study, we investigated recurrent copy number variations (CNVs) in the 19p12 locus, which are associated with neurodevelopmental disorders. The two genes in this locus, ZNF675 and ZNF681, arose via gene duplication in primates, and their presence in several pathological CNVs in the human population suggests that either or both of these genes are required for normal human brain development. ZNF675 and ZNF681 are members of the Krüppel-associated box zinc finger (KZNF) protein family, a class of transcriptional repressors important for epigenetic silencing of specific genomic regions. About 170 primate-specific KZNFs are present in the human genome. Although KZNFs are primarily associated with repressing retrotransposon-derived DNA, evidence is emerging that they can be co-opted for other gene regulatory processes. We show that genetic deletion of ZNF675 causes developmental defects in cortical organoids, and our data suggest that part of the observed neurodevelopmental phenotype is mediated by a gene regulatory role of ZNF675 on the promoter of the neurodevelopmental gene Hes family BHLH transcription factor 1 (HES1). We also find evidence for the recently evolved regulation of genes involved in neurological disorders, microcephalin 1 and sestrin 3. We show that ZNF675 interferes with HES1 auto-inhibition, a process essential for the maintenance of neural progenitors. As a striking example of how some KZNFs have integrated into preexisting gene expression networks, these findings suggest the emergence of ZNF675 has caused a change in the balance of HES1 autoregulation. The association of ZNF675 CNV with human developmental disorders and ZNF675-mediated regulation of neurodevelopmental genes suggests that it evolved into an important factor for human brain development.

DDX3X syndrome: From clinical phenotypes to biological insights.

DDX3X syndrome is a neurodevelopmental disorder accounting for up to 3% of cases of intellectual disability (ID) and affecting primarily females. Individuals diagnosed with DDX3X syndrome can also present with behavioral challenges, motor delays and movement disorders, epilepsy, and congenital malformations. DDX3X syndrome is caused by mutations in the X-linked gene DDX3X, which encodes a DEAD-box RNA helicase with critical roles in RNA metabolism, including mRNA translation. Emerging discoveries from animal models are unveiling a fundamental role of DDX3X in neuronal differentiation and development, especially in the neocortex. Here, we review the current knowledge of genetic and neurobiological mechanisms underlying DDX3X syndrome and their relationship with clinical phenotypes.

Paediatric Magnetoencephalography and its Role in Neurodevelopmental Disorders.

Magnetoencephalography (MEG) is a non-invasive neuroimaging technique that assesses neurophysiology, through detection of the magnetic fields generated by neural currents. In this way, it is sensitive to brain activity, both in individual regions and brain-wide networks. Conventional MEG systems employ an array of sensors that must be cryogenically cooled to low temperature, in a rigid one-size-fits-all helmet. Systems are typically designed to fit adults and are therefore challenging to use for paediatric measurements. Despite this, MEG has been employed successfully in research to investigate neurodevelopmental disorders, and clinically for presurgical planning for paediatric epilepsy. Here, we review the applications of MEG in children, specifically focussing on autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD). Our review demonstrates the significance of MEG in furthering our understanding of these neurodevelopmental disorders, whilst also highlighting the limitations of current instrumentation. We also consider the future of paediatric MEG, with a focus on newly developed instrumentation based on optically pumped magnetometers (OPM-MEG). We provide a brief overview of the development of OPM-MEG systems, and how this new technology might enable investigation of brain function in very young children and infants.

Sex-Differential Gene Expression in Developing Human Cortex and Its Intersection With Autism Risk Pathways.

Background: Sex-differential biology may contribute to the consistently male-biased prevalence of autism spectrum disorder (ASD). Gene expression differences between males and females in the brain can indicate possible molecular and cellular mechanisms involved, although transcriptomic sex differences during human prenatal cortical development have been incompletely characterized, primarily due to small sample sizes. Methods: We performed a meta-analysis of sex-differential expression and co-expression network analysis in 2 independent bulk RNA sequencing datasets generated from cortex of 273 prenatal donors without known neuropsychiatric disorders. To assess the intersection between neurotypical sex differences and neuropsychiatric disorder biology, we tested for enrichment of ASD-associated risk genes and expression changes, neuropsychiatric disorder risk genes, and cell type markers within identified sex-differentially expressed genes (sex-DEGs) and sex-differential co-expression modules. Results: We identified 101 significant sex-DEGs, including Y-chromosome genes, genes impacted by X-chromosome inactivation, and autosomal genes. Known ASD risk genes, implicated by either common or rare variants, did not preferentially overlap with sex-DEGs. We identified 1 male-specific co-expression module enriched for immune signaling that is unique to 1 input dataset. Conclusions: Sex-differential gene expression is limited in prenatal human cortex tissue, although meta-analysis of large datasets allows for the identification of sex-DEGs, including autosomal genes that encode proteins involved in neural development. Lack of sex-DEG overlap with ASD risk genes in the prenatal cortex suggests that sex-differential modulation of ASD symptoms may occur in other brain regions, at other developmental stages, or in specific cell types, or may involve mechanisms that act downstream from mutation-carrying genes.

Males are more commonly diagnosed with autism spectrum disorder than females, and sex differences in brain development may contribute to this difference. Here, we define differences in gene expression patterns between males and females in human prenatal brain tissue from 273 donors to identify 101 genes that are expressed at different levels in males and females and gene sets that show sex-specific expression correlations. Genes with autism-associated DNA variants and genes with altered expression in autism do not preferentially overlap with sex-differential genes, suggesting that sex-differential biology may influence autism risk mechanisms in other brain regions, at other developmental stages, or in specific cell types.

Generating Neuroimmune Assembloids Using Human Induced Pluripotent Stem Cell (iPSC)-Derived Cortical Organoids and Microglia.

The emergence of brain organoids has revolutionized our understanding of neurodevelopment and neurological diseases by providing an in vitro model system that recapitulates key aspects of human brain development. However, conventional organoid protocols often overlook the role of microglia, the resident immune cells of the central nervous system. Microglia dysfunction is implicated in various neurological disorders, highlighting the need for their inclusion in organoid models. Here, we present a novel method for generating neuroimmune assembloids using human-induced pluripotent stem cell (iPSC)-derived cortical organoids and microglia. Building upon our previous work generating myelinating cortical organoids, we extend our methodology to include the integration of microglia, ensuring their long-term survival and maturation within the organoids. We describe two integration methods: one involving direct addition of microglia progenitors to the organoids and an alternative approach where microglia and dissociated neuronal progenitors are aggregated together in a defined ratio. To facilitate downstream analysis, we also describe a dissociation protocol for single-cell RNA sequencing (scRNA-seq) and provide guidance on fixation, cryosectioning, and immunostaining of assembloid structures. Overall, our protocol provides a comprehensive framework for generating neuroimmune assembloids, offering researchers a valuable tool for studying the interactions between neural cell types and immune cells in the context of neurological diseases.

SETDB1 regulates short interspersed nuclear elements and chromatin loop organization in mouse neural precursor cells.

BACKGROUND: Transposable elements play a critical role in maintaining genome architecture during neurodevelopment. Short Interspersed Nuclear Elements (SINEs), a major subtype of transposable elements, are known to harbor binding sites for the CCCTC-binding factor (CTCF) and pivotal in orchestrating chromatin organization. However, the regulatory mechanisms controlling the activity of SINEs in the developing brain remains elusive. RESULTS: In our study, we conduct a comprehensive genome-wide epigenetic analysis in mouse neural precursor cells using ATAC-seq, ChIP-seq, whole genome bisulfite sequencing, in situ Hi-C, and RNA-seq. Our findings reveal that the SET domain bifurcated histone lysine methyltransferase 1 (SETDB1)-mediated H3K9me3, in conjunction with DNA methylation, restricts chromatin accessibility on a selective subset of SINEs in neural precursor cells. Mechanistically, loss of Setdb1 increases CTCF access to these SINE elements and contributes to chromatin loop reorganization. Moreover, de novo loop formation contributes to differential gene expression, including the dysregulation of genes enriched in mitotic pathways. This leads to the disruptions of cell proliferation in the embryonic brain after genetic ablation of Setdb1 both in vitro and in vivo. CONCLUSIONS: In summary, our study sheds light on the epigenetic regulation of SINEs in mouse neural precursor cells, suggesting their role in maintaining chromatin organization and cell proliferation during neurodevelopment.

Early Morbidities of Hypoxia-Ischemic Encephalopathy in Term Neonates With a Resistive Index as a Prognostic Indicator.

Background Acidosis, hypoxemia, and hypercarbia are symptoms of a syndrome known as perinatal asphyxia that occurs during the first and second stages of labor and shortly after delivery due to poor gas exchange. The Doppler technique is a non-invasive way to assess the risk of neurodevelopment damage in hypoxic-ischemic encephalopathy (HIE) that may be done at the patient's bedside without disturbing them. The study aims to evaluate cranial ultrasound findings in HIE and investigate the role of resistive index (RI) values assessed by color Doppler transcranial ultrasonography in predicting early morbidities in neonates with HIE within 72 hours of life. Methodology Prospective observational research was carried out at the north Karnataka region's tertiary newborn critical care unit. The study included 54 infants with HIE in total. The male-to-female ratio was 1.7:1, with 34 (63%) male and 20 (37%) female newborns. Results About 32 instances had grade I HIE, 8 had grade II HIE, and 14 had grade III HIE. In 35 instances (64.81%), the RI was normal; in 19 cases (35.19%), it was abnormal. Increased periventricular density and cerebral parenchyma echo density were common Doppler ultrasonography findings. Roughly 93% of people survived, and 7% of people died from HIE. Seizures (12.96%) and acute renal damage (33.33%) were the most frequent consequences. Conclusion In instances of HIE, the RI was revealed to be a favorable predictive indicator for newborn prognosis. Counseling and educating parents about early morbidities, anticipated long-term consequences, and the need for follow-up will all benefit from it. Additionally, color Doppler is a practical and secure diagnostic method for determining a newborn's level of HIE.

Examining the association between prenatal cannabis exposure and child autism traits: A multi-cohort investigation in the environmental influences on child health outcome program.

This study examined the association between prenatal cannabis exposure and autism spectrum disorder (ASD) diagnoses and traits. A total sample of 11,570 children (ages 1-18; 53% male; 25% Hispanic; 60% White) from 34 cohorts of the National Institutes of Health-funded environmental influences on child health outcomes consortium were included in analyses. Results from generalized linear mixed models replicated previous studies showing that associations between prenatal cannabis exposure and ASD traits in children are not significant when controlling for relevant covariates, particularly tobacco exposure. Child biological sex did not moderate the association between prenatal cannabis exposure and ASD. In a large sample and measuring ASD traits continuously, there was no evidence that prenatal cannabis exposure increases the risk for ASD. This work helps to clarify previous mixed findings by addressing concerns about statistical power and ASD measurement.

Long-term follow-up in congenital diaphragmatic hernia.

With improvements in initial care for patients with congenital diaphragmatic hernia (CDH), the number of CDH patients with severe disease who are surviving to discharge has increased. This growing population of patients faces a unique set of long-term challenges, multisystem adverse outcomes, and post-intervention complications requiring specialized multidisciplinary follow-up. Early identification and intervention are essential to mitigate the potential morbidity associated with these challenges. This manuscript outlines a general framework for long-term follow-up for the CDH patient, including cardiopulmonary, gastrointestinal, neurodevelopmental, surgical, and quality of life outcomes.

Ubiquitin system mutations in neurological diseases.

Neuronal ubiquitin balance impacts the fate of countless cellular proteins, and its disruption is associated with various neurological disorders. The ubiquitin system is critical for proper neuronal cell state transitions and the clearance of misfolded or aggregated proteins that threaten cellular integrity. This article reviews the state of and recent advancements in our understanding of the disruptions to components of the ubiquitin system, in particular E3 ligases and deubiquitylases, in neurodevelopmental and neurodegenerative diseases. Specific focus is on enzymes with recent progress in their characterization, including identifying enzyme-substrate pairs, the use of stem cell and animal models, and the development of therapeutics for ubiquitin-related diseases.

The role of microglia in early neurodevelopment and the effects of maternal immune activation.

Activation of the maternal immune system during gestation has been associated with an increased risk for neurodevelopmental disorders in the offspring, particularly schizophrenia and autism spectrum disorder. Microglia, the tissue-resident macrophages of the central nervous system, are implicated as potential mediators of this increased risk. Early in development, microglia start populating the embryonic central nervous system and in addition to their traditional role as immune responders under homeostatic conditions, microglia are also intricately involved in various early neurodevelopmental processes. The timing of immune activation may interfere with microglia functioning during early neurodevelopment, potentially leading to long-term consequences in postnatal life. In this review we will discuss the involvement of microglia in brain development during the prenatal and early postnatal stages of life, while also examining the effects of maternal immune activation on microglia and neurodevelopmental processes. Additionally, we discuss recent single cell RNA-sequencing studies focusing on microglia during prenatal development, and hypothesize how early life microglial priming, potentially through epigenetic reprogramming, may be related to neurodevelopmental disorders.

De novo monoallelic Reelin missense variants act in a dominant-negative manner causing neuronal migration disorders.

Reelin (RELN) is a secreted glycoprotein essential for cerebral cortex development. In humans, recessive RELN variants cause cortical and cerebellar malformations, while heterozygous variants were associated to epilepsy, autism and mild cortical abnormalities. However, their functional effects remain unknown. We identified inherited and de novo RELN missense variants in heterozygous patients with neuronal migration disorders (NMDs) as diverse as pachygyria and polymicrogyria. We investigated in culture and in the developing mouse cerebral cortex how different variants impacted RELN function. Polymicrogyria-associated variants behaved as gain-of-function showing an enhanced ability to induce neuronal aggregation, while those linked to pachygyria as loss-of-function leading to defective neuronal aggregation/migration. The pachygyria-associated de novo heterozygous RELN variants acted as dominant-negative by preventing wild-type RELN secretion in culture, animal models and patients, thereby causing dominant NMDs. We demonstrated how mutant RELN proteins in vitro and in vivo predict cortical malformation phenotypes, providing valuable insights into the pathogenesis of such disorders.