Factors In Neurodevelopmental Disorders Research Articles

The Role of Bcl11 Transcription Factors in Neurodevelopmental Disorders.

Neurodevelopmental disorders (NDDs) comprise a diverse group of diseases, including developmental delay, autism spectrum disorder (ASD), intellectual disability (ID), and attention-deficit/hyperactivity disorder (ADHD). NDDs are caused by aberrant brain development due to genetic and environmental factors. To establish specific and curative therapeutic approaches, it is indispensable to gain precise mechanistic insight into the cellular and molecular pathogenesis of NDDs. Mutations of BCL11A and BCL11B, two closely related, ultra-conserved zinc-finger transcription factors, were recently reported to be associated with NDDs, including developmental delay, ASD, and ID, as well as morphogenic defects such as cerebellar hypoplasia. In mice, Bcl11 transcription factors are well known to orchestrate various cellular processes during brain development, for example, neural progenitor cell proliferation, neuronal migration, and the differentiation as well as integration of neurons into functional circuits. Developmental defects observed in both, mice and humans display striking similarities, suggesting Bcl11 knockout mice provide excellent models for analyzing human disease. This review offers a comprehensive overview of the cellular and molecular functions of Bcl11a and b and links experimental research to the corresponding NDDs observed in humans. Moreover, it outlines trajectories for future translational research that may help to better understand the molecular basis of Bcl11-dependent NDDs as well as to conceive disease-specific therapeutic approaches.

Stem-cell derived neurosphere assay highlights the effects of viral infection on human cortical development

Aberrant cortical development is a key feature of neurodevelopmental disorders such as autism spectrum disorder and schizophrenia. Both genetic and environmental risk factors are thought to contribute to defects in cortical development; however, model systems that can capture the dynamic process of human cortical development are not well established. To address this challenge, we combined recent progress in induced pluripotent stem cell differentiation with advanced live cell imaging techniques to establish a novel three-dimensional neurosphere assay, amenable to genetic and environmental modifications, to investigate key aspects of human cortical development in real-time. For the first time, we demonstrate the ability to visualise and quantify radial glial extension and neural migration through live cell imaging. To show proof-of-concept, we used our neurosphere assay to study the effect of a simulated viral infection, a well-established environmental risk factor in neurodevelopmental disorders, on cortical development. This was achieved by exposing neurospheres to the viral mimic, polyinosinic:polycytidylic acid. The results showed significant reductions in radial glia growth and neural migration in three independent differentiations. Further, fixed imaging highlighted reductions in the HOPX-expressing outer radial glia scaffolding and a consequent decrease in the migration of CTIP2-expressing cortical cells. Overall, our results provide new insight into how infections may exert deleterious effects on the developing human cortex.

Dexmedetomidine Protects Cerebellar Neurons against Hyperoxia-Induced Oxidative Stress and Apoptosis in the Juvenile Rat.

The risk of oxidative stress is unavoidable in preterm infants and increases the risk of neonatal morbidities. Premature infants often require sedation and analgesia, and the commonly used opioids and benzodiazepines are associated with adverse effects. Impairment of cerebellar functions during cognitive development could be a crucial factor in neurodevelopmental disorders of prematurity. Recent studies have focused on dexmedetomidine (DEX), which has been associated with potential neuroprotective properties and is used as an off-label application in neonatal units. Wistar rats (P6) were exposed to 80% hyperoxia for 24 h and received as pretreatment a single dose of DEX (5µg/kg, i.p.). Analyses in the immature rat cerebellum immediately after hyperoxia (P7) and after recovery to room air (P9, P11, and P14) included examinations for cell death and inflammatory and oxidative responses. Acute exposure to high oxygen concentrations caused a significant oxidative stress response, with a return to normal levels by P14. A marked reduction of hyperoxia-mediated damage was demonstrated after DEX pretreatment. DEX produced a much earlier recovery than in controls, confirming a neuroprotective effect of DEX on alterations elicited by oxygen stress on the developing cerebellum.

Characterization of SETD1A haploinsufficiency in humans and Drosophila defines a novel neurodevelopmental syndrome.

Defects in histone methyltransferases (HMTs) are major contributing factors in neurodevelopmental disorders (NDDs). Heterozygous variants of SETD1A involved in histone H3 lysine 4 (H3K4) methylation were previously identified in individuals with schizophrenia. Here, we define the clinical features of the Mendelian syndrome associated with haploinsufficiency of SETD1A by investigating 15 predominantly pediatric individuals who all have de novo SETD1A variants. These individuals present with a core set of symptoms comprising global developmental delay and/or intellectual disability, subtle facial dysmorphisms, behavioral and psychiatric problems. We examined cellular phenotypes in three patient-derived lymphoblastoid cell lines with three variants: p.Gly535Alafs*12, c.4582-2_4582delAG, and p.Tyr1499Asp. These patient cell lines displayed DNA damage repair defects that were comparable to previously observed RNAi-mediated depletion of SETD1A. This suggested that these variants, including the p.Tyr1499Asp in the catalytic SET domain, behave as loss-of-function (LoF) alleles. Previous studies demonstrated a role for SETD1A in cell cycle control and differentiation. However, individuals with SETD1A variants do not show major structural brain defects or severe microcephaly, suggesting that defective proliferation and differentiation of neural progenitors is unlikely the single underlying cause of the disorder. We show here that the Drosophila melanogaster SETD1A orthologue is required in postmitotic neurons of the fly brain for normal memory, suggesting a role in post development neuronal function. Together, this study defines a neurodevelopmental disorder caused by dominant de novo LoF variants in SETD1A and further supports a role for H3K4 methyltransferases in the regulation of neuronal processes underlying normal cognitive functioning.

Environmental Chemical Diethylhexyl Phthalate Alters Intestinal Microbiota Community Structure and Metabolite Profile in Mice.

Exposure to environmental chemicals during windows of development is a potentially contributing factor in gut microbiota dysbiosis and linked to chronic diseases and developmental disorders. We used a community-level model of microbiota metabolism to investigate the effects of diethylhexyl phthalate (DEHP), a ubiquitous plasticizer implicated in neurodevelopmental disorders, on the composition and metabolite outputs of gut microbiota in young mice. Administration of DEHP by oral gavage increased the abundance of Lachnoclostridium, while decreasing Clostridium sensu stricto Addition of DEHP to in vitro-cultured cecal microbiota increased the abundance of Paenibacillus and Lachnoclostridium Untargeted metabolomics showed that DEHP broadly altered the metabolite profile in the culture. Notably, DEHP enhanced the production of p-cresol while inhibiting butyrate synthesis. Metabolic model-guided correlation analysis indicated that the likely sources of p-cresol are Clostridium species. Monoculture of Lachnoclostridium bolteae confirmed that it is capable of producing p-hydroxyphenylacetic acid, the immediate precursor of p-cresol, and that the species' growth is enhanced upon DEHP exposure. Taken together, these findings suggest a model where DEHP increases production of p-cresol, a bacterial metabolite linked with neurodevelopmental disorders, by expanding the abundance of species that synthesize the metabolite's precursor.IMPORTANCE Several previous studies have pointed to environmental chemical exposure during windows of development as a contributing factor in neurodevelopmental disorders and correlated these disorders with microbiota dysbiosis; however, little is known about how the chemicals specifically alter the microbiota to interfere with development. The findings reported in this paper unambiguously establish that a pollutant linked with neurodevelopmental disorders can directly modify the microbiota to promote the production of a potentially toxic metabolite (p-cresol) that has also been correlated with neurodevelopmental disorders. Furthermore, we used a novel modeling strategy to identify the responsible enzymes and bacterial sources of this metabolite. To the best of our knowledge, the present study is the first to characterize the functional consequence of phthalate exposure on a developed microbiota. Our results suggest that specific bacterial pathways could be developed as diagnostic and therapeutic targets against health risks posed by ingestion of environmental chemicals.

Does environmental exposure to the greenhouse gas, N2O, contribute to etiological factors in neurodevelopmental disorders? A mini-review of the evidence.

Neurodevelopmental disorders are increasing in prevalence worldwide. Previous work suggests that exposure to the environmental air pollutant and greenhouse gas - nitrous oxide (N2O) - may be an etiological factor in neurodevelopmental disorders through the targeting of several neural correlates. While a number of recent systematic reviews have addressed the role of general anesthesia in the surgical setting and neurodevelopmental outcomes, a narrative mini-review was conducted to first define and characterize the relevant variables (i.e., N2O, attention-deficit hyperactivity disorder [ADHD] and autism spectrum disorders [ASD]) and their potential interactions into a coherent, hypothesis-generating work. The narrative mini-review merges basic principles in environmental science, anesthesiology, and psychiatry to more fully develop the novel hypotheses that neurodevelopmental impairment found in conditions like ADHD and ASD may be due to exposure to the increasing air pollutant, N2O. The results of the present mini-review indicate that exposure to N2O, even at non-toxic doses, may modulate central neurotransmission and target many neural substrates directly implicated in neurodevelopmental disorders, including the glutamatergic, opioidergic, cholinergic, and dopaminergic systems. Epidemiological studies also indicate that early and repeated exposure to general anesthesia, including N2O, may contribute to later adverse neurodevelopmental outcomes in children. The current evidence and subsequent hypotheses suggest that a renewed interest be taken in the toxicological assessment of environmental N2O exposure using validated biomarkers and psychiatric endpoints. Given the relevance of N2O as a greenhouse gas, societies may also wish to engage in a more robust monitoring and reporting of N2O levels in the environment for climactic benefit as well.

High rate of disease-related copy number variations in childhood onset schizophrenia

Copy number variants (CNVs) are risk factors in neurodevelopmental disorders, including autism, epilepsy, intellectual disability (ID) and schizophrenia. Childhood onset schizophrenia (COS), defined as onset before the age of 13 years, is a rare and severe form of the disorder, with more striking array of prepsychotic developmental disorders and abnormalities in brain development. Because of the well-known phenotypic variability associated with pathogenic CNVs, we conducted whole genome genotyping to detect CNVs and then focused on a group of 46 rare CNVs that had well-documented risk for adult onset schizophrenia (AOS), autism, epilepsy and/or ID. We evaluated 126 COS probands, 69 of which also had a healthy full sibling. When COS probands were compared with their matched related controls, significantly more affected individuals carried disease-related CNVs (P=0.017). Moreover, COS probands showed a higher rate than that found in AOS probands (P<0.0001). A total of 15 (11.9%) subjects exhibited at least one such CNV and four of these subjects (26.7%) had two. Five of 15 (4.0% of the sample) had a 2.5-3 Mb deletion mapping to 22q11.2, a rate higher than that reported for adult onset (0.3-1%) (P<0.001) or autism spectrum disorder and, indeed, the highest rate reported for any clinical population to date. For one COS subject, a duplication found at 22q13.3 had previously only been associated with autism, and for four patients CNVs at 8q11.2, 10q22.3, 16p11.2 and 17q21.3 had only previously been associated with ID. Taken together, these findings support the well-known pleiotropic effects of these CNVs suggesting shared abnormalities early in brain development. Clinically, broad CNV-based population screening is needed to assess their overall clinical burden.

Calculation of Mercury’s Effects on Neurodevelopment

Bellinger (2012) recently estimated the loss of cognitive function in terms of Full-Scale intelligence quotient (IQ) in children exposed to certain environmental chemicals. To ascertain pre-natal exposures of methyl-mercury (MeHg) in children, he used exposure data on mercury (Hg) concentrations in hair of U.S. women of childbearing age (16–49 years) from NHANES (National Health and Nutrition Examination Survey) 1999–2000 (McDowell et al. 2004). Bellinger applied a regression coefficient of –0.18 IQ points per microgram per gram increase in maternal hair as calculated by Axelrad et al. (2007). However, the results of Axelrad et al. (2007) relied on incomplete data from a prospective study in the Faroe Islands and on non-adjusted results from the Seychelles study, later found to be confounded by nutrients from seafood (Strain et al. 2008). Bellinger (2012) then applied the regression coefficient to hair Hg levels > 1.11 µg/g (90th percentile), because this level corresponds to the reference dose of MeHg established many years ago. Assuming a concentration of 1.73 µg/g (95th percentile) as the midpoint (rather than the average, which is higher) for the hair Hg levels of the 10% of U.S. women with a level > 1.11 µg/g, he estimated a total IQ loss of 284,580 points. We believe that Bellinger’s general approach is sound but that the dose–response information is outdated, a caveat that Bellinger noted, although it was not reflected in the summary table. We therefore wish to complement these calculations using updated dose–response data. Prospective data justify a lower threshold Hg level of 0.58 µg/g hair corresponding to 50% of the reference dose (Grandjean and Budtz-Jorgensen 2007). In addition, a 1-µg/g increase in hair Hg concentration is more likely associated with an average adverse impact of 0.465 IQ points, as discussed by Pichery et al. (2012). Assuming a log- normal exposure distribution, a 75th percentile hair Hg concentration of 0.42 µg/g, and a 90th percentile of 1.11 µg/g as reported by McDowell et al. (2004), we estimate that 18.5% of women exceed a threshold of 0.58 µg/g hair Hg and that the average concentration for 0.58–1.11 µg/g is approximately 0.8 µg/g. For the sake of comparing these values with Bellinger’s calculations (Bellinger 2012), we used a median concentration of 1.73 µg/g as the average hair Hg level of the 10% of U.S. women with a level > 1.11 µg/g. On the basis of these assumptions, we calculated a total IQ loss for the U.S. population of children 0–5 years of age (n = 25.5 million) to be 1,590,000 IQ points, or 264,000 IQ points per year. We recently used similar calculations to estimate the annual costs of Hg pollution in France (Pichery et al. 2012), a country one-fifth the size of the United States. At slightly higher exposure levels, the annual loss in IQ points was estimated to be 157,000. Greater losses were obtained using a log-scale effect (Pichery et al. 2012). With an estimated value of each IQ point of $18,000 in terms of life-time earnings, the current loss of IQ points associated with MeHg exposure represents a very substantial value to society.

CDKL5 gene status in female patients with epilepsy and Rett-like features: two new mutations in the catalytic domain

BackgroundMutations in the cyclin-dependent kinase-like 5 gene (CDKL5) located in the Xp22 region have been shown to cause a subset of atypical Rett syndrome with infantile spasms or early seizures starting in the first postnatal months.MethodsWe performed mutation screening of CDKL5 in 60 female patients who had been identified as negative for the methyl CpG-binding protein 2 gene (MECP2) mutations, but who had current or past epilepsy, regardless of the age of onset, type, and severity. All the exons in the CDKL5 gene and their neighbouring sequences were examined, and CDKL5 rearrangements were studied by multiplex ligation-dependent probe amplification (MLPA).ResultsSix previously unidentified DNA changes were detected, two of which were disease-causing mutations in the catalytic domain: a frameshift mutation (c.509_510insGT; p.Glu170GlyfsX36) and a complete deletion of exon 10. Both were found in patients with seizures that started in the first month of life.ConclusionsThis study demonstrated the importance of CDKL5 mutations as etiological factors in neurodevelopmental disorders, and indicated that a thorough analysis of the CDKL5 gene sequence and its rearrangements should be considered in females with Rett syndrome-like phenotypes, severe encephalopathy and epilepsy with onset before 5 months of age. This study also confirmed the usefulness of MLPA as a diagnostic screening method for use in clinical practice.

Mouse Models of Genetic and Environmental Factors in Neurodevelopmental Disorders

Mouse Models of Genetic and Environmental Factors in Neurodevelopmental Disorders

Autism and Increased Paternal Age Related Changes in Global Levels of Gene Expression Regulation

A causal role of mutations in multiple general transcription factors in neurodevelopmental disorders including autism suggested that alterations in global levels of gene expression regulation might also relate to disease risk in sporadic cases of autism. This premise can be tested by evaluating for changes in the overall distribution of gene expression levels. For instance, in mice, variability in hippocampal-dependent behaviors was associated with variability in the pattern of the overall distribution of gene expression levels, as assessed by variance in the distribution of gene expression levels in the hippocampus. We hypothesized that a similar change in variance might be found in children with autism. Gene expression microarrays covering greater than 47,000 unique RNA transcripts were done on RNA from peripheral blood lymphocytes (PBL) of children with autism (n = 82) and controls (n = 64). Variance in the distribution of gene expression levels from each microarray was compared between groups of children. Also tested was whether a risk factor for autism, increased paternal age, was associated with variance. A decrease in the variance in the distribution of gene expression levels in PBL was associated with the diagnosis of autism and a risk factor for autism, increased paternal age. Traditional approaches to microarray analysis of gene expression suggested a possible mechanism for decreased variance in gene expression. Gene expression pathways involved in transcriptional regulation were down-regulated in the blood of children with autism and children of older fathers. Thus, results from global and gene specific approaches to studying microarray data were complimentary and supported the hypothesis that alterations at the global level of gene expression regulation are related to autism and increased paternal age. Global regulation of transcription, thus, represents a possible point of convergence for multiple etiologies of autism and other neurodevelopmental disorders.

Spatiotemporal Molecular Approach of in utero Electroporation to Functionally Decipher Endophenotypes in Neurodevelopmental Disorders

We have only just begun to decipher the complexity of our brain, including its maturation. Correct brain development and communication among brain areas are crucial for proper cognitive behavior. Brain area-specific genes expressed within a particular time window direct neurodevelopmental events such as proliferation, migration, axon guidance, dendritic arborization, and synaptogenesis. These genes can pose as susceptibility factors in neurodevelopmental disorders eventually resulting in area-specific cognitive deficits. Therefore, in utero electroporation (IUE)-mediated gene transfer can aid in creating valuable animal models in which the regionality and time of expression can be restricted for the targeted gene(s). Moreover, through the use of cell-type-specific molecular constructs, expression can be altered in a particular neuronal subset within a distinct area such that we are now able to causally link the function of that gene in that brain region to the etiology of the disorder. Thus, IUE-mediated gene transfer is an attractive molecular technique to spatiotemporally address the developmental aspects of gene function in relation to neurodevelopmental disorder-associated endophenotypes.

Could oxidative stress be a factor in neurodevelopmental disorders?

There is evidence of co-morbidity in the neurodevelopmental disorders and they display depletion of polyunsaturated fatty acids (PUFAs) in their plasma and red cell membranes. This suggests an abnormal fatty acid metabolism, which may affect cell signalling and synthesis of eicosanoids. This common feature in the neurodevelopmental disorders may be genetic in origin: however, oxidative stress may also contribute to decreased PUFAs found in these disorders.