Maternal infection during pregnancy and risk of autism spectrum disorders: A systematic review and meta-analysis

Effect of in utero exposure to SARS-CoV-2 infection on pregnancy outcomes and growth and development of infants: protocol for a multicentre ambispective cohort study in India

INTRODUCTION

Poor pregnancy and neonatal outcomes in infants born to COVID-19 positive mothers have been reported, but there is insufficient evidence regarding subsequent growth and development of these children. Our study aims to explore the effect of in-utero exposure to SARS-CoV-2 on pregnancy outcomes and growth and development of infants.

METHODS AND ANALYSIS

A multicentric ambispective cohort study with comparison group (1:1) will be conducted at six sites. A total of 2400 participants (exposure cohort, n=1200; comparison cohort, n=1200), ie, 400 participants from each site (200 retrospectively; 200 prospectively) will be included. Exposure cohort will be infants born to women with documented COVID-19 infection anytime during pregnancy and comparison cohort will be infants born to women who did not test positive for SARS-CoV-2 anytime during pregnancy. All infants will be followed up till 1 year of age. Anthropometric measurement, age of attainment of developmental milestones and clinical examination findings will be recorded at each follow-up. Data regarding possible cofactors affecting the outcomes will be collected from both groups and adjusted for during analysis. The two groups will be compared for prevalence of every variable considered in the study. Relative risk, attributable and population attributable risks will be calculated. All risk factors with p<0.1 on bivariate analysis will be subjected to multiple logistic regression analysis. A final multivariable model will be developed by including the statistically significant risk factors.

ETHICS AND DISSEMINATION

The study has been approved by the Institutional Review Board of IIHMR Delhi (IRB/2021-2022/006) and will be required to be approved at all participating study sites. The study is scheduled from September 2021 to August 2023. Data from retrospective cohort will be reported by August 2022. All participants will provide written informed consent. We plan to publish our results in a peer-reviewed journal and present findings at academic conferences.

Cerebellar and Striatal Implications in Autism Spectrum Disorders: From Clinical Observations to Animal Models

Autism spectrum disorders (ASD) are complex conditions that stem from a combination of genetic, epigenetic and environmental influences during early pre- and postnatal childhood. The review focuses on the cerebellum and the striatum, two structures involved in motor, sensory, cognitive and social functions altered in ASD. We summarize clinical and fundamental studies highlighting the importance of these two structures in ASD. We further discuss the relation between cellular and molecular alterations with the observed behavior at the social, cognitive, motor and gait levels. Functional correlates regarding neuronal activity are also detailed wherever possible, and sexual dimorphism is explored pointing to the need to apprehend ASD in both sexes, as findings can be dramatically different at both quantitative and qualitative levels. The review focuses also on a set of three recent papers from our laboratory where we explored motor and gait function in various genetic and environmental ASD animal models. We report that motor and gait behaviors can constitute an early and quantitative window to the disease, as they often correlate with the severity of social impairments and loss of cerebellar Purkinje cells. The review ends with suggestions as to the main obstacles that need to be surpassed before an appropriate management of the disease can be proposed.

Prenatal influenza vaccination or influenza infection and autism spectrum disorder in offspring

BACKGROUND

As prenatal vaccinations continue to be given more frequently, it is important to assess long-term safety events. This study investigates the association between prenatal influenza vaccination or infection and autism spectrum disorder (ASD) risk in offspring.

METHODS

Retrospective cohort study of mother-child pairs with deliveries 1/1/2011-12/31/2014 at Kaiser Permanente Southern California was performed. Children >1 year were followed through 12/31/2018. Maternal influenza vaccination or infection during pregnancy was obtained from electronic health records. ASD was defined by International Classification of Diseases, 9th/10th Revision codes after age 1 year. Cox proportional hazards models estimated the crude and inverse probability of treatment weighted (IPTW) hazard ratios (HR) for the association between maternal influenza vaccination or infection and ASD.

RESULTS

There were 84,739 mother-child pairs included in the final analytic sample. Maternal vaccination coverage increased slightly over time, from 52.7% for 2011 births to 59.6% for 2014 births. Of the 46,257 women vaccinated, 32.4% were vaccinated during the 1 st trimester, 41.8% during the 2 nd trimester, and 25.8% during the 3 rd trimester. ASD was diagnosed in 1,930 (2.3%) children. The IPTW analyses showed no association between prenatal influenza vaccination or infection and ASD in offspring (HR: 1.04, 95% confidence interval [CI]: 0.95, 1.13; HR: 1.12, 95% CI: 0.66, 1.89, respectively).

CONCLUSIONS

Prenatal influenza vaccination or infection was not associated with ASD risk in offspring. The findings support recommendations to vaccinate pregnant women to protect themselves and their infants, both of whom are vulnerable to severe morbidity following infection.

A feature of maternal sleep apnea during gestation causes autism-relevant neuronal and behavioral phenotypes in offspring

Mounting epidemiologic and scientific evidence indicates that many psychiatric disorders originate from a complex interplay between genetics and early life experiences, particularly in the womb. Despite decades of research, our understanding of the precise prenatal and perinatal experiences that increase susceptibility to neurodevelopmental disorders remains incomplete. Sleep apnea (SA) is increasingly common during pregnancy and is characterized by recurrent partial or complete cessations in breathing during sleep. SA causes pathological drops in blood oxygen levels (intermittent hypoxia, IH), often hundreds of times each night. Although SA is known to cause adverse pregnancy and neonatal outcomes, the long-term consequences of maternal SA during pregnancy on brain-based behavioral outcomes and associated neuronal functioning in the offspring remain unknown. We developed a rat model of maternal SA during pregnancy by exposing dams to IH, a hallmark feature of SA, during gestational days 10 to 21 and investigated the consequences on the offspring's forebrain synaptic structure, synaptic function, and behavioral phenotypes across multiples stages of development. Our findings represent a rare example of prenatal factors causing sexually dimorphic behavioral phenotypes associated with excessive (rather than reduced) synapse numbers and implicate hyperactivity of the mammalian target of rapamycin (mTOR) pathway in contributing to the behavioral aberrations. These findings have implications for neuropsychiatric disorders typified by superfluous synapse maintenance that are believed to result, at least in part, from largely unknown insults to the maternal environment.

Maternal infection during pregnancy and the risk of attention-deficit/hyperactivity disorder in the offspring: A systematic review and meta-analysis

BACKGROUND

The effects of maternal infection during pregnancy on the risk of attention-deficit/hyperactivity disorder (ADHD) in the offspring are unclear, and no overview is available.

METHODS

We searched the PubMed and EMBASE databases for relevant studies and performed a systematic review and meta-analysis of the literature.

RESULTS

We found that that maternal infection during pregnancy was associated with a small increase in the risk of ADHD (OR 1.25, 95% CI 1.09, 1.44, P < 0.0001; I² = 92.9%, p < 0.0001) in the offspring. In subgroup analyses, the association remained for maternal genitourinary (GU) infection (OR, 1.19, 1.12, 1.27, P < 0.001; I² = 0%; p = 0.517). However, there was no significant association when we pooled data from siblings from other pregnancies (OR = 1.06, 95% CI, 0.99-1.13, P = 0.084; I² = 0%; p = 0.859), implying that the association was due to confounding.

CONCLUSIONS

The statistically significant association between maternal infection during pregnancy and ADHD in the offspring can be partially explained by unmeasured confounding.

Prenatal Maternal Infections and Children's Neurodevelopment in the UK Millennium Cohort Study: A Focus on ASD and ADHD

OBJECTIVE

No clear answer has yet been attained as to the influence of prenatal exposure to infection on autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD), either alone or as co-occurring issues. The current study examined links between hospital-recorded and maternal-reported prenatal infections and ASD, ADHD, and co-occurring ASD and ADHD.

METHODS

Participants were n = 15,462 children and mother pairs from the Millennium Cohort Study (MCS), a population-representative UK sample.

RESULTS

Findings show associations between maternal-reported infections and ASD, and some evidence of links with ADHD and co-occurring ASD and ADHD. Hospital-recorded infections were not found to be associated with ASD, ADHD, or their co-occurrence. Agreement between hospital-recorded and maternal-reported infections was low, which may explain the discrepant findings.

CONCLUSION

Prenatal maternal infections may be associated with increased odds of ASD and ADHD. Findings point to the importance of drawing on multiple sources of information when ascertaining prenatal infection status.

Pathogenic Infections during Pregnancy and the Consequences for Fetal Brain Development

Pathogens comprised of viruses, bacteria, gut microbiome, and parasites are a leading cause of ever-emerging diseases in humans. Studying pathogens for their ability to cause diseases is a topic of critical discussion among scientists and pharmaceutical centers for effective drug development that diagnose, treat, and prevent infection-associated disorders. Pathogens impact health either directly by invading the host or by eliciting an acute inflammatory immune response. This paradigm of inflammatory immune responses is even more consequential in people who may be immunocompromised. In this regard, pregnancy offers an altered immunity scenario, which may allow the onset of severe diseases. Viruses, such as Influenza, HIV, and now SARS-CoV-2, associated with the COVID-19 pandemic, raise new concerns for maternal and fetal/neonatal health. Intrauterine bacterial and parasitic infections are also known to impact pregnancy outcomes and neonatal health. More importantly, viral and bacterial infections during pregnancy have been identified as a common contributor to fetal brain development defects. Infection-mediated inflammatory uterine immune milieu is thought to be the main trigger for causing poor fetal brain development, resulting in long-term cognitive impairments. The concept of in utero programming of childhood and adult disorders has revolutionized the field of neurodevelopment and its associated complications. Recent findings in mice and humans clearly support the idea that uterine immunity during pregnancy controls the health trajectory of the child and considerably influences the cognitive function and mental health. In this review, we focus on the in utero programming of autism spectrum disorders (ASD) and assess the effects of pathogens on the onset of ASD-like symptoms.

Abnormal mTOR Activity in Pediatric Autoimmune Neuropsychiatric and MIA-Associated Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by the early onset of communication and behavioral problems. ASD is highly heritable; however, environmental factors also play a considerable role in this disorder. A significant part of both syndromic and idiopathic autism cases could be attributed to disorders caused by mammalian target of rapamycin (mTOR)-dependent translation deregulation. This narrative review analyzes both bioinformatic and experimental evidence that connects mTOR signaling to the maternal autoantibody-related (MAR) autism spectrum and autoimmune neuropsychiatric disorders simultaneously. In addition, we reconstruct a network presenting the interactions between the mTOR signaling and eight MAR ASD genes coding for ASD-specific maternal autoantibody target proteins. The research discussed in this review demonstrates novel perspectives and validates the need for a subtyping of ASD on the grounds of pathogenic mechanisms. The utter necessity of designing ELISA-based test panels to identify all antibodies related to autism-like behavior is also considered.

Early life environmental factors associated with autism spectrum disorder symptoms in children at age 2 years: A birth cohort study

LAY ABSTRACT

Mounting evidence indicates the contribution of early life environmental factors in autism spectrum disorder. We aim to report the prospective associations between early life environmental factors and autism spectrum disorder symptoms in children at the age of 2 years in a population-derived birth cohort, the Barwon Infant Study. Autism spectrum disorder symptoms at the age of 2 years strongly predicted autism spectrum disorder diagnosis by the age of 4 years (area under curve = 0.93; 95% CI (0.82, 1.00)). After adjusting for child's sex and age at the time of behavioural assessment, markers of socioeconomic disadvantage, such as lower household income and lone parental status; maternal health factors, including younger maternal age, maternal pre-pregnancy body mass index, higher gestational weight gain and prenatal maternal stress; maternal lifestyle factors, such as prenatal alcohol and environmental air pollutant exposures, including particulate matter < 2.5 μm at birth, child secondhand tobacco smoke at 12 months, dampness/mould and home heating with oil, kerosene or diesel heaters at 2 years postnatal. Lower socioeconomic indexes for area, later birth order, higher maternal prenatal depression and maternal smoking frequency had a dose-response relationship with autism spectrum disorder symptoms. Future studies on environmental factors and autism spectrum disorder should consider the reasons for the socioeconomic disparity and the combined impact of multiple environmental factors through common mechanistic pathways.

Influence of Prenatal Drug Exposure, Maternal Inflammation, and Parental Aging on the Development of Autism Spectrum Disorder

Autism spectrum disorder (ASD) affects reciprocal social interaction and produces abnormal repetitive, restrictive behaviors and interests. The diverse causes of ASD are divided into genetic alterations and environmental risks. The prevalence of ASD has been rising for several decades, which might be related to environmental risks as it is difficult to consider that the prevalence of genetic disorders related to ASD would increase suddenly. The latter includes (1) exposure to medications, such as valproic acid (VPA) and selective serotonin reuptake inhibitors (SSRIs) (2), maternal complications during pregnancy, including infection and hypertensive disorders of pregnancy, and (3) high parental age. Epidemiological studies have indicated a pathogenetic role of prenatal exposure to VPA and maternal inflammation in the development of ASD. VPA is considered to exert its deleterious effects on the fetal brain through several distinct mechanisms, such as alterations of γ-aminobutyric acid signaling, the inhibition of histone deacetylase, the disruption of folic acid metabolism, and the activation of mammalian target of rapamycin. Maternal inflammation that is caused by different stimuli converges on a higher load of proinflammatory cytokines in the fetal brain. Rodent models of maternal exposure to SSRIs generate ASD-like behavior in offspring, but clinical correlations with these preclinical findings are inconclusive. Hypertensive disorders of pregnancy and advanced parental age increase the risk of ASD in humans, but the mechanisms have been poorly investigated in animal models. Evidence of the mechanisms by which environmental factors are related to ASD is discussed, which may contribute to the development of preventive and therapeutic interventions for ASD.

Microglia: Synaptic modulator in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by variable impairment of social communication and repetitive behaviors, highly restricted interests, and/or sensory behaviors beginning early in life. Many individuals with ASD have dysfunction of microglia, which may be closely related to neuroinflammation, making microglia play an important role in the pathogenesis of ASD. Mounting evidence indicates that microglia, the resident immune cells of the brain, are required for proper brain function, especially in the maintenance of neuronal circuitry and control of behavior. Dysfunction of microglia will ultimately affect the neural function in a variety of ways, including the formation of synapses and alteration of excitatory-inhibitory balance. In this review, we provide an overview of how microglia actively interact with neurons in physiological conditions and modulate the fate and functions of synapses. We put a spotlight on the multi-dimensional neurodevelopmental roles of microglia, especially in the essential influence of synapses, and discuss how microglia are currently thought to influence ASD progression.

Maternal Immune Activation and Interleukin 17A in the Pathogenesis of Autistic Spectrum Disorder and Why It Matters in the COVID-19 Era

Autism spectrum disorder (ASD) is the commonest neurodevelopmental disability. It is a highly complex disorder with an increasing prevalence and an unclear etiology. Consensus indicates that ASD arises as a genetically modulated, and environmentally influenced condition. Although pathogenic rare genetic variants are detected in around 20% of cases of ASD, no single factor is responsible for the vast majority of ASD cases or that explains their characteristic clinical heterogeneity. However, a growing body of evidence suggests that ASD susceptibility involves an interplay between genetic factors and environmental exposures. One such environmental exposure which has received significant attention in this regard is maternal immune activation (MIA) resulting from bacterial or viral infection during pregnancy. Reproducible rodent models of ASD are well-established whereby induction of MIA in pregnant dams, leads to offspring displaying neuroanatomical, functional, and behavioral changes analogous to those seen in ASD. Blockade of specific inflammatory cytokines such as interleukin-17A during gestation remediates many of these observed behavioral effects, suggesting a causative or contributory role. Here, we review the growing body of animal and human-based evidence indicating that interleukin-17A may mediate the observed effects of MIA on neurodevelopmental outcomes in the offspring. This is particularly important given the current corona virus disease-2019 (COVID-19) pandemic as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during pregnancy is a potent stimulator of the maternal immune response, however the long-term effects of maternal SARS-CoV-2 infection on neurodevelopmental outcomes is unclear. This underscores the importance of monitoring neurodevelopmental outcomes in children exposed to SARS-CoV-2-induced MIA during gestation.

Maternal and Adult Interleukin-17A Exposure and Autism Spectrum Disorder

Epidemiological evidence in humans has suggested that maternal infections and maternal autoimmune diseases are involved in the pathogenesis of autism spectrum disorder. Animal studies supporting human results have shown that maternal immune activation causes brain and behavioral alterations in offspring. Several underlying mechanisms, including interleukin-17A imbalance, have been identified. Apart from the pro-inflammatory effects of interleukin-17A, there is also evidence to support the idea that it activates neuronal function and defines cognitive behavior. In this review, we examined the signaling pathways in both immunological and neurological contexts that may contribute to the improvement of autism spectrum disorder symptoms associated with maternal blocking of interleukin-17A and adult exposure to interleukin-17A. We first describe the epidemiology of maternal immune activation then focus on molecular signaling of the interleukin-17 family regarding its physiological and pathological roles in the embryonic and adult brain. In the future, it may be possible to use interleukin-17 antibodies to prevent autism spectrum disorder.

The Developing Microbiome From Birth to 3 Years: The Gut-Brain Axis and Neurodevelopmental Outcomes

The volume and breadth of research on the role of the microbiome in neurodevelopmental and neuropsychiatric disorders has expanded greatly over the last decade, opening doors to new models of mechanisms of the gut-brain axis and therapeutic interventions to reduce the burden of these outcomes. Studies have highlighted the window of birth to 3 years as an especially sensitive window when interventions may be the most effective. Harnessing the powerful gut-brain axis during this critical developmental window clarifies important investigations into the microbe-human connection and the developing brain, affording opportunities to prevent rather than treat neurodevelopmental disorders and neuropsychiatric illness. In this review, we present an overview of the developing intestinal microbiome in the critical window of birth to age 3; and its prospective relationship with neurodevelopment, with particular emphasis on immunological mechanisms. Next, the role of the microbiome in neurobehavioral outcomes (such as autism, anxiety, and attention-deficit hyperactivity disorder) as well as cognitive development are described. In these sections, we highlight the importance of pairing mechanistic studies in murine models with large scale epidemiological studies that aim to clarify the typical health promoting microbiome in early life across varied populations in comparison to dysbiosis. The microbiome is an important focus in human studies because it is so readily alterable with simple interventions, and we briefly outline what is known about microbiome targeted interventions in neurodevelopmental outcomes. More novel examinations of known environmental chemicals that adversely impact neurodevelopmental outcomes and the potential role of the microbiome as a mediator or modifier are discussed. Finally, we look to the future and emphasize the need for additional research to identify populations that are sensitive to alterations in their gut microbiome and clarify how interventions might correct and optimize neurodevelopmental outcomes.

The Brain-Gut-Microbiome System: Pathways and Implications for Autism Spectrum Disorder

Gastrointestinal dysfunction is one of the most prevalent physiological symptoms of autism spectrum disorder (ASD). A growing body of largely preclinical research suggests that dysbiotic gut microbiota may modulate brain function and social behavior, yet little is known about the mechanisms that underlie these relationships and how they may influence the pathogenesis or severity of ASD. While various genetic and environmental risk factors have been implicated in ASD, this review aims to provide an overview of studies elucidating the mechanisms by which gut microbiota, associated metabolites, and the brain interact to influence behavior and ASD development, in at least a subgroup of individuals with gastrointestinal problems. Specifically, we review the brain-gut-microbiome system and discuss findings from current animal and human studies as they relate to social-behavioral and neurological impairments in ASD, microbiota-targeted therapies (i.e., probiotics, fecal microbiota transplantation) in ASD, and how microbiota may influence the brain at molecular, structural, and functional levels, with a particular interest in social and emotion-related brain networks. A deeper understanding of microbiome-brain-behavior interactions has the potential to inform new therapies aimed at modulating this system and alleviating both behavioral and physiological symptomatology in individuals with ASD.

Maternal immune-related conditions during pregnancy may be a risk factor for neuropsychiatric problems in offspring throughout childhood and adolescence

BACKGROUND

Emerging research suggests that maternal immune activation (MIA) may be associated with an increased risk of adverse neurodevelopmental and mental health outcomes in offspring. Using data from the Raine Study, we investigated whether MIA during pregnancy was associated with increased behavioral and emotional problems in offspring longitudinally across development.

METHODS

Mothers (Generation 1; N = 1905) were classified into the following categories: AAAE (Asthma/Allergy/Atopy/Eczema; N = 1267); infection (during pregnancy; N = 1082); no AAAE or infection (N = 301). The Child Behavior Checklist (CBCL) was administered for offspring at ages 5, 8, 10, 14, and 17. Generalized estimating equations were used to investigate the effect of maternal immune status on CBCL scores.

RESULTS

AAAE conditions were associated with significant increases in CBCL Total (β 2.49; CI 1.98-3.00), Externalizing (β 1.54; CI 1.05-2.03), and Internalizing (β 2.28; CI 1.80-2.76) scores. Infection conditions were also associated with increased Total (β 1.27; CI 0.77-1.78), Externalizing (β 1.18; CI 0.70-1.66), and Internalizing (β 0.76; CI 0.28-1.24) scores. Exposure to more than one AAAE and/or infection condition was associated with a greater elevation in CBCL scores than single exposures in males and females. Females showed greater increases on the Internalizing scale from MIA, while males showed similar increases on both Internalizing and Externalizing scales.

CONCLUSIONS

MIA was associated with increased behavioral and emotional problems in offspring throughout childhood and adolescence. This highlights the need to understand the relationship between MIA, fetal development, and long-term outcomes, with the potential to advance early identification and intervention strategies.

MCP-1 Signaling Disrupts Social Behavior by Modulating Brain Volumetric Changes and Microglia Morphology

Autism spectrum disorder (ASD) is a disease characterized by reduced social interaction and stereotypic behaviors and related to macroscopic volumetric changes in cerebellar and somatosensory cortices (SPP). Epidemiological and preclinical models have confirmed that a proinflammatory profile during fetal development increases ASD susceptibility after birth. Here, we aimed to globally identify the effect of maternal exposure to high-energy dense diets, which we refer to as cafeteria diet (CAF) on peripheral and central proinflammatory profiles, microglia reactivity, and volumetric brain changes related to assisting defective social interaction in the mice offspring. We found a sex-dependent effect of maternal exposure to CAF diet or inoculation of the dsARN mimetic Poly (I:C) on peripheral proinflammatory and social interaction in the offspring. Notably, maternal exposure to CAF diet impairs social interaction and favors an increase in anxiety in male but not female offspring. Also, CAF diet exposure or Poly (I:C) inoculation during fetal programming promote peripheral proinflammatory profile in the ASD-diagnosed male but not in females. Selectively, we found a robust accumulation of the monocyte chemoattractant protein-1 (MCP-1) in plasma of ASD-diagnosed males exposed to CAF during fetal development. Biological assessment of MCP-1 signaling in brain confirms that systemic injection of MCP-1-neutralizing antibody reestablished social interaction and blocked anxiety, accompanied by a reduction in cerebellar lobule X (CbX) volume and an increase volume of the primary somatosensory (SSP) cortex in male offspring. These data highlight the contribution of diet-dependent MCP-1 signaling on volumetric brain changes and microglia morphology promoting ASD-like behavior in male mice.

Maternal immune activation downregulates schizophrenia genes in the foetal mouse brain

Susceptibility to schizophrenia is mediated by genetic and environmental risk factors. Maternal immune activation by infections during pregnancy is hypothesized to be a key environmental risk factor. However, little is known about how maternal immune activation contributes to schizophrenia pathogenesis. In this study, we investigated if maternal immune activation influences the expression of genes associated with schizophrenia in foetal mouse brains. We found that two sets of schizophrenia genes were downregulated more than expected by chance in the foetal mouse brain following maternal immune activation, namely those genes associated with schizophrenia through genome-wide association study (fold change = 1.93, false discovery rate = 4 × 10-4) and downregulated genes in adult schizophrenia brains (fold change = 1.51, false discovery rate = 4 × 10-10). We found that these genes mapped to key biological processes, such as neuronal cell adhesion. We also identified cortical excitatory neurons and inhibitory interneurons as the most vulnerable cell types to the deleterious effects of this interaction. Subsequently, we used gene expression information from herpes simplex virus 1 infection of neuronal precursor cells as orthogonal evidence to support our findings and to demonstrate that schizophrenia-associated cell adhesion genes, PCDHA2, PCDHA3 and PCDHA5, were downregulated following herpes simplex virus 1 infection. Collectively, our results provide novel evidence for a link between genetic and environmental risk factors in schizophrenia pathogenesis. These findings carry important implications for early preventative strategies in schizophrenia.

The Role of Maternal Immune Activation in the Pathogenesis of Autism: A Review of the Evidence, Proposed Mechanisms and Implications for Treatment

Autism spectrum disorder (ASD) is a neurodevelopmental disease that is characterized by a deficit in social interactions and communication, as well as repetitive and restrictive behaviors. Increasing lines of evidence suggest an important role for immune dysregulation and/or inflammation in the development of ASD. Recently, a relationship between inflammation, oxidative stress, and mitochondrial dysfunction has been reported in the brain tissue of individuals with ASD. Some recent studies have also reported oxidative stress and mitochondrial abnormalities in animal models of maternal immune activation (MIA). This review is focused on the hypothesis that MIA induces microglial activation, oxidative stress, and mitochondrial dysfunction, a deleterious trio in the brain that can lead to neuroinflammation and neurodevelopmental pathologies in offspring. Infection during pregnancy activates the mother’s immune system to release proinflammatory cytokines, such as IL-6, TNF-α, and others. Furthermore, these cytokines can directly cross the placenta and enter the fetal circulation, or activate resident immune cells, resulting in an increased production of proinflammatory cytokines, including IL-6. Proinflammatory cytokines that cross the blood–brain barrier (BBB) may initiate a neuroinflammation cascade, starting with the activation of the microglia. Inflammatory processes induce oxidative stress and mitochondrial dysfunction that, in turn, may exacerbate oxidative stress in a self-perpetuating vicious cycle that can lead to downstream abnormalities in brain development and behavior.

Maternal immune activation as a risk factor for psychiatric illness in the context of the SARS-CoV-2 pandemic

Inflammation, due to infectious pathogens or other non-infectious stimuli, during pregnancy is associated with elevated risk for neurodevelopmental disorders such as schizophrenia and autism in the offspring. Although historically identified through retrospective epidemiologic studies, the relationship between maternal immune activation and offspring neurodevelopmental disease risk is now well established because of clinical studies which utilized prospective birth cohorts, serologically confirmed infection records, and subsequent long-term offspring follow-up. These efforts have been corroborated by preclinical research which demonstrates anatomical, biochemical, and behavioural alterations that resemble the clinical features of psychiatric illnesses. Intervention studies further demonstrate causal roles of inflammatory mediators, such as cytokines, in these long-lasting changes in behaviour and brain. This review summarizes a selection of maternal immune activation literature that explores the relationship between these inflammatory mediators and the neuropsychiatric-like effects later observed in the offspring. This literature is presented alongside emerging information regarding SARS-CoV-2 infection in pregnancy, with discussion of how these data may inform future research regarding the effects of the present coronavirus pandemic on emerging birth cohorts.

Increased incidence of childhood mental disorders following exposure to early life infection

Early life exposure to infectious diseases confers risk for adult psychiatric disorders but relatively few human population studies have examined associations with childhood mental disorder. Here we examined the effects of exposure to maternal infection during pregnancy, and child infectious diseases in early childhood (birth to age 4 years), in relation to first mental disorder diagnosis (age 5-13 years). The study sample comprised 71,841 children represented in a population cohort of children in New South Wales, Australia, followed from birth to early adolescence via linkage of administrative registers. Childhood exposure to infectious disease was determined during the prenatal period (i.e., maternal infection during gestation), and in early childhood (between birth and age 4 years) using the NSW Ministry of Health Admitted Patients data collection. Days to first diagnosis with a mental disorder was determined from recorded diagnoses between age 5-13 years in the NSW Ministry of Health's Admitted Patients, Emergency Department and Mental Health Ambulatory data collections. While crude hazard ratios for both prenatal infection and childhood infection exposures indicated significantly earlier diagnosis with mental disorders associated with both of these risk factors, only childhood infection exposure was associated with higher adjusted hazard ratios (aHR) for any diagnoses (aHR = 1.21, 95% CI = 1.11-1.32), externalising disorders (aHR = 1.45, 95% CI 1.18-1.79) and developmental disorders (aHR = 1.82, 95% CI 1.49-2.22) when the effects of maternal and early childhood (age < 5 years) mental disorders were taken into account. Exposure to infectious diseases during early childhood, but not prenatal infection exposure, appears to be associated with earlier diagnosis of mental disorders in childhood.

Prenatal maternal infections and children's socioemotional development: findings from the UK Millennium Cohort Study

Previous research suggests that prenatal maternal infections may be associated with increased odds of children having a neurodevelopmental disorder. However, little evidence exists on associations with broader child outcomes, especially subclinical symptoms. Participants were the N = 14,021 members of the population-representative UK Millennium Cohort Study. We examined associations between prenatal maternal infections, both maternal-reported and hospital-recorded, and children's socioemotional development, using the Strengths and Difficulties Questionnaire (SDQ) at age three. Maternal-reported prenatal infections were associated with increased emotional symptoms, after adjusting for several potential confounds and covariates. Hospital-recorded prenatal infections were not associated with children's socioemotional outcomes, after adjusting for potential confounding and covarying factors. Findings suggest that prenatal maternal infections, particularly those which the mothers remember months later, may be associated with increased emotional problems in early childhood. This emphasises the need for screening for and preventing infections during pregnancy. Further, the occurrence of prenatal infection indicates the potential need for early intervention for children's emotional difficulties.

Pregnant Mothers' Medical Claims and Associated Risk of Their Children being Diagnosed with Autism Spectrum Disorder

A retrospective analysis of administrative claims containing a diverse mixture of ages, ethnicities, and geographical regions across the United States was conducted in order to identify medical events that occur during pregnancy and are associated with autism spectrum disorder (ASD). The dataset used in this study is comprised of 123,824 pregnancies of which 1265 resulted in the child being diagnosed with ASD during the first five years of life. Logistic regression analysis revealed significant relationships between several maternal medical claims, made during her pregnancy and segmented by trimester, and the child's diagnosis of ASD. Having a biological sibling with ASD, maternal use of antidepressant medication and psychiatry services as well as non-pregnancy related claims such hospital visits, surgical procedures, and radiology exposure were related to an increased risk of ASD regardless of trimester. Urinary tract infections during the first trimester and preterm delivery during the second trimester were also related to an increased risk of ASD. Preventative and obstetrical care were associated with a decreased risk for ASD. A better understanding of the medical factors that increase the risk of having a child with ASD can lead to strategies to decrease risk or identify those children who require increased surveillance for the development of ASD to promote early diagnosis and intervention.

Maternal Mid-Gestation Cytokine Dysregulation in Mothers of Children with Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a developmental disorder characterised by deficits in social interactions and communication, with stereotypical and repetitive behaviours. Recent evidence suggests that maternal immune dysregulation may predispose offspring to ASD. Independent samples t-tests revealed downregulation of IL-17A concentrations in cases, when compared to controls, at both 15 weeks (p = 0.02), and 20 weeks (p = 0.02), which persisted at 20 weeks following adjustment for confounding variables. This adds to the growing body of evidence that maternal immune regulation may play a role in foetal neurodevelopment.

Maternal immune activation and neuroinflammation in human neurodevelopmental disorders

Maternal health during pregnancy plays a major role in shaping health and disease risks in the offspring. The maternal immune activation hypothesis proposes that inflammatory perturbations in utero can affect fetal neurodevelopment, and evidence from human epidemiological studies supports an association between maternal inflammation during pregnancy and offspring neurodevelopmental disorders (NDDs). Diverse maternal inflammatory factors, including obesity, asthma, autoimmune disease, infection and psychosocial stress, are associated with an increased risk of NDDs in the offspring. In addition to inflammation, epigenetic factors are increasingly recognized to operate at the gene-environment interface during NDD pathogenesis. For example, integrated brain transcriptome and epigenetic analyses of individuals with NDDs demonstrate convergent dysregulated immune pathways. In this Review, we focus on the emerging human evidence for an association between maternal immune activation and childhood NDDs, including autism spectrum disorder, attention-deficit/hyperactivity disorder and Tourette syndrome. We refer to established pathophysiological concepts in animal models, including immune signalling across the placenta, epigenetic 'priming' of offspring microglia and postnatal immune-brain crosstalk. The increasing incidence of NDDs has created an urgent need to mitigate the risk and severity of these conditions through both preventive strategies in pregnancy and novel postnatal therapies targeting disease mechanisms.

Viral model of maternal immune activation alters placental AMPK and mTORC1 signaling in rats

INTRODUCTION

Maternal immune activation (MIA) is associated with neurodevelopmental disorders in offspring. We previously demonstrated that poly(I:C)-mediated MIA alters placental and fetal brain amino acid transporter expression in rats, which could potentially play a role in altered neurodevelopment; however, the mechanism(s) underlying these changes in amino acid transporter expression remain unknown. The objective of the current study was to investigate the mechanism(s) underlying poly(I:C)-mediated changes in the expression of the amino acid transporters in the placenta.

METHODS

Pregnant rats received poly(I:C) on gestational day 14 and placentas were collected 6 h later. Mass spectrometry-based proteomics of placentas was performed followed by pathway enrichment analysis. Activation of mTORC1 and its upstream regulator, AMPK, was investigated using immunoblotting. Finally, the role of mTORC1 and AMPK in regulating the expression and localization of the amino acid transporters EAAT2 and ASCT1 was investigated in the human choriocarcinoma cell line JAR.

RESULTS

The impact of poly(I:C) on the placental proteome was highly sexually dimorphic. While proteomics-based pathway enrichment analysis indicated enrichment of mTOR signaling in male placentas only, further investigation revealed inhibition of mTORC1 in both male and female placentas in addition to activation of AMPK. In vitro, activation of AMPK and inhibition of mTORC1 decreased membrane localization of EAAT2 and ASCT1.

DISCUSSION

Poly(I:C)-mediated MIA activates AMPK and inhibits mTORC1 in rat placenta, both of which decrease expression and membrane localization of EAAT2 and ASCT1 in vitro. Thus, AMPK/mTORC1 signaling could be a novel treatment target for alleviating MIA-mediated changes in placental amino acid transport.

Investigating associations between birth order and autism diagnostic phenotypes

BACKGROUND

Birth order effects have been linked to variability in intelligence, educational attainment and sexual orientation. First- and later-born children have been linked to an increased likelihood of an Autism Spectrum Disorder (ASD) diagnosis, with a smaller body of evidence implicating decreases in cognitive functioning with increased birth order. The present study investigated the potential association between birth order and ASD diagnostic phenotypes in a large and representative population sample.

METHODS

Data were obtained from an ongoing prospective diagnostic registry, collected between 1999 and 2017, including children (1-18 years of age, n = 5,404) diagnosed with ASD in the state of Western Australia. Children with ASD were ranked relative to sibling's birth to establish birth order within families at time of ASD diagnosis. Information reported to the registry by health professionals at the time of diagnostic evaluation included demographic and family characteristics, functional abilities and intellectual capacity.

RESULTS

Adaptive functioning and intelligence scores decreased with increasing birth order, with later-born children more likely to have an intellectual disability. Compared to first-born children with siblings, first-born children without siblings at the time of diagnosis also exhibited decreased cognitive functioning.

CONCLUSIONS

These findings demonstrate for the first time an association between increasing birth order and variability in ASD clinical phenotypes at diagnosis, with potential evidence of reproductive curtailment in children without siblings. Taken together, these findings have significant implications for advancing understanding about the potential mechanisms that contribute to heterogeneity in ASD clinical presentations as a function of birth order and family size.

Hyperactivation of the amygdala correlates with impaired social play behavior of prepubertal male rats in a maternal immune activation model

Maternal infection during pregnancy is an environmental risk factor for neurodevelopmental dysfunction, such as autism spectrum disorder (ASD). This study investigated the effect of maternal immune activation (MIA) on the behavior profile of prepubertal offspring and whether MIA alters the neuronal activation pattern of brain areas related to social play behavior. Pregnant Wistar rats received 500 μg/kg of lipopolysaccharide or saline solution on gestational day 16. Their offspring were tested using behavioral tasks to capture some of the core and associated ASD-like symptoms. Neuronal activation, indexed via c-fos expression after social play behavior, was evaluated in several brain areas. MIA had a number of adverse effects on dams and reduced the number of successful births and litter size. MIA induced sex-specific autistic-like features by a reduction in ultrasonic vocalizations in response to separation from the mother and nest, reduction in discrimination between neutral odors and their nest odor, moderate effect in stereotypies in the hole-board test, impaired risk assessment phenotype, and reduction in social play behavior without changes in locomotor activity only in prepubertal male offspring. A decrease in social play behavior may be associated with a decrease in the number of c-fos-positive cells in the prefrontal cortex and striatum, but hyperactivation of the basolateral and basomedial amygdala. Prenatal immune challenge results in ASD-like symptoms such as impaired risk assessment behavior, communication, and social interactions in male prepubertal offspring. Impaired social play behavior is correlated with neuronal hyperactivation in the amygdala.

Adapting and validating the Autism Diagnostic Interview - Revised for use with deaf children and young people

LAY ABSTRACT

Autism assessment processes need to improve for deaf children as they are currently being diagnosed later than their hearing counterparts and misdiagnosis can occur. We took one of the most commonly used parent developmental interviews for autism spectrum disorder the Autism Diagnostic Interview-Revised and adapted it using international expert advice. Modifications were proposed and agreed by the expert panel for 45% of items; the remaining 55% of items were unchanged. We then tested the revised version, adapted for deaf children (Autism Diagnostic Interview-Revised Deaf Adaptation), in a UK sample of 78 parents/carers of deaf children with autism spectrum disorder and 126 parents/carers with deaf children without autism spectrum disorder. When compared to National Institute for Health and Care Excellence guideline standard clinical assessments, the Autism Diagnostic Interview-Revised Deaf Adaptation diagnostic algorithm threshold scores could identify those deaf children with a definite diagnosis (true autism spectrum disorder positives) well (sensitivity of 89% (79%-96%)) and those deaf children who did not have autism spectrum disorder (true autism spectrum disorder negatives) well (specificity of 81% (70%-89%)). Our findings indicate that the Autism Diagnostic Interview-Revised Deaf Adaptation is likely to prove a useful measure for the assessment of deaf children with suspected autism spectrum disorder and that further research would be helpful.

Physiological mediators of prenatal environmental influences in autism spectrum disorder

Recent research has pointed to the importance of the prenatal environment in the etiology of autism spectrum disorder (ASD) but the biological mechanisms which mitigate these environmental factors are not clear. Mitochondrial metabolism abnormalities, inflammation and oxidative stress as common physiological disturbances associated with ASD. Network analysis of the scientific literature identified several leading prenatal environmental factors associated with ASD, particularly air pollution, pesticides, the microbiome and epigenetics. These leading prenatal environmental factors were found to be most associated with inflammation, followed by oxidative stress and mitochondrial dysfunction. Other prenatal factors associated with ASD not identified by the network analysis were also found to be significantly associated with these common physiological disturbances. A better understanding of the biological mechanism which mediate the effect of prenatal environmental factors can lead to insights of how ASD develops and the development of targeted therapeutics to prevent ASD from occuring.

Novel treatments for autism spectrum disorder based on genomics and systems biology

BACKGROUND

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder with a complex underlying genetic architecture. There are currently no known pharmacologic treatments for the core ASD symptoms of social deficits and restricted/ repetitive behavior. However, there are dozens of clinical trials currently underway that are testing the impact of novel and existing agents on core and associated symptoms in ASD.

METHODS

We present a narrative synthesis of the historical and contemporary challenges to drug discovery in ASD. We then provide an overview of novel treatments currently under investigation from a genomics and systems biology perspective.

RESULTS

Data driven network and cluster analyses suggest alterations in transcriptional regulation, chromatin remodelling, synaptic transmission, neuropeptide signalling, and/or immunological mechanisms may contribute to or underlie the development of ASD. Agents and upcoming trials targeting each of the above listed systems are reviewed.

CONCLUSION

Identifying effective pharmacologic treatments for the core and associated symptom domains in ASD will require further collaboration and innovation in the areas of outcome measurement, biomarker research, and genomics, as well as systematic efforts to identify and treat subgroups of individuals with ASD who may be differentially responsive to specific treatments.

Correlation analysis of expression of CC and CXC chemokines in children with autism spectrum disorder

To investigate the relationship between the expression of CC and CXC chemokines and autism spectrum disorder (ASD).A total of 62 children with ASD (ASD group) and 60 gender- and age-matched normal children (control group) admitted to our hospital from January 2019 to January 2020 were included in the study. Monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1α (MIP-1α), macrophage inflammatory protein-1β (MIP-1β), regulated upon activation, normal T-cell expressed and secreted (RANTES), interleukin-8 (IL-8), monokine induced by interferon (IFN)-γ (MIG), and purified human interferon-γ-induced protein-10 (IP-10) were detected in the ASD group. The correlation between the above indexes and the severity of the ASD group was analyzed.Significantly increased MCP-1 levels (P < .01) along with the markedly decreased MIP-1α and MIP-1β levels (P < .01) were detected in the venous blood of the ASD group compared with the control group. In addition, they exhibited no significant difference (yet a downward trend) in the level of RANTES (P > .05). Children in the ASD group showed significantly decreased IP-10 levels (P < .01); however, they had no noticeable change (yet a decreasing trend) in the levels of IL-8 and MIG (P > .05). MCP-1 level was positively related to the Module 1 scores of Autism Diagnostic Observation Schedule-second edition (ADOS-2), whereas the levels of Childhood Autism Rating Scale MIP-1α, MIP-1β, IL-8, IP-10, and MIG were negatively correlated with the ADOS-2 Module 1 scores (P < .01). However, no significant correlation was found between RANTES and the ADOS-2 Module 1 scores (P > .05).The levels of CC chemokines (MCP-1, MIP-1α, MIP-1β, and RANTES) and CXC chemokines (IL-8, IP-10, and MIG) are positively correlated with the pathogenesis of ASD. Inflammation is an important contributing factor to ASD.

Prenatal maternal infection and risk for autism in offspring: A meta-analysis

While prenatal maternal infection has received attention as a preventable and treatable risk factor for autism, findings have been inconsistent. This paper presents the results of a meta-analysis to determine whether the weight of the evidence supports such an association. Studies with a categorical diagnosis of autism as the outcome and an assessment of its association with prenatal maternal infection or fever (or the data necessary to compute this association) were included. A total of 36 studies met these criteria. Two independent reviewers extracted data on study design, methods of assessment, type of infectious agent, site of infection, trimester of exposure, definition of autism, and effect size. Analyses demonstrated a statistically significant association of maternal infection/fever with autism in offspring (OR = 1.32; 95% CI = 1.20-1.46). Adjustment for evident publication bias slightly weakened this association. There was little variation in effect sizes across agent or site of infection. Small differences across trimester of exposure were not statistically significant. There was some evidence that recall bias associated with status on the outcome variable leads to differential misclassification of exposure status. Nonetheless, the overall association is only modestly reduced when studies potentially contaminated by such bias are removed. Although causality has not been firmly established, these findings suggest maternal infection during pregnancy confers an increase in risk for autism in offspring. Given the prevalence of this risk factor, it is possible that the incidence of autism would be reduced by 12%-17% if maternal infections could be prevented or safely treated in a timely manner. LAY SUMMARY: This study is a meta-analysis of the association of maternal infection during pregnancy and subsequent autism in offspring. In combining the results from 36 studies of this association we find that a significant relationship is present. The association does not vary much across the types of infections or when they occur during pregnancy. We conclude that the incidence of autism could be substantially reduced if maternal infections could be prevented or safely treated in a timely manner.

Prenatal origins of neuropsychiatric diseases

AIM

The main objective is to review the available evidence in the literature for developmental origins of neuropsychiatric diseases and their underlying mechanisms. We also probe emerging cutting-edge prenatal MR imaging tools and their future role in advancing our understanding the prenatal footprints of neuropsychiatric disorders.

OBSERVATIONS

Both human and animal studies support early intrauterine origins of neuropsychiatric disease, particularly autism spectrum disorders (ASD), attention and hyperactivity disorders, schizophrenia, depression, anxiety and mood disorders. Specific mechanisms of intrauterine injury include infection, inflammation, hypoxia, hypoperfusion, ischaemia polysubstance use/abuse, maternal mental health and placental dysfunction.

CONCLUSIONS AND RELEVANCE

There is ample evidence to suggest developmental vulnerability of the foetal brain to intrauterine exposures that increases and individual's risk for neuropsychiatric disease, especially the risk of ASD, depression and anxiety. Elucidating the exact timing and mechanisms of injury can be difficult and require novel, non-invasive approaches to the study emerging structural and functional brain development of the foetus. Clinical care should both emphasise maternal health during pregnancy, as well as close, continued monitoring for at risk offspring throughout young adulthood for the early identification and treatment of neuropsychiatric diseases.

Diet-induced dysbiosis of the maternal gut microbiome in early life programming of neurodevelopmental disorders

The maternal gut microbiome plays a critical role in fetal and early postnatal development, shaping fundamental processes including immune maturation and brain development, among others. Consequently, it also contributes to fetal programming of health and disease. Over the last decade, epidemiological studies and work in preclinical animal models have begun to uncover a link between dysbiosis of the maternal gut microbiome and neurodevelopmental disorders in offspring. Neurodevelopmental disorders are caused by both genetic and environmental factors, and their interactions; however, clinical heterogeneity, phenotypic variability, and comorbidities make identification of underlying mechanisms difficult. Among environmental factors, exposure to maternal obesity in utero confers a significant increase in risk for neurodevelopmental disorders. Obesogenic diets in humans, non-human primates, and rodents induce functional modifications in maternal gut microbiome composition, which animal studies suggest are causally related to adverse mental health outcomes in offspring. Here, we review evidence linking maternal diet-induced gut dysbiosis to neurodevelopmental disorders and discuss how it could affect pre- and early postnatal brain development. We are hopeful that this burgeoning field of research will revolutionize antenatal care by leading to accessible prophylactic strategies, such as prenatal probiotics, to improve mental health outcomes in children affected by maternal diet-induced obesity.

Dynamics of cortical progenitors and production of subcerebral neurons are altered in embryos of a maternal inflammation model for autism

The broad impairments in cognitive and neurologic functioning found in Autism Spectrum Disorder (ASD) patients are thought to originate during early prenatal developmental stages. Indeed, postmortem and imaging studies in ASD patients detected white-matter abnormalities, as well as prefrontal and temporal cortex deficits, evident from early childhood. Here, we used Maternal Immune Activation (MIA), a mouse model for ASD, in which the offsprings exhibit Autistic-like behaviors as well as cortical abnormalities. However, the dynamics that influence the number and the identity of newly born cortical neurons following maternal inflammation remains unknown. Our study shows early changes in the duration of the S-phase of PAX6⁺ progenitors, leading to an increased proportion of neurogenic divisions and a reciprocal decrease in the proliferative divisions. In two different time points of maternal inflammation, MIA resulted in an overproduction of CTIP2⁺ cortical neurons, which remained overrepresented at the end of gestation and in postnatal mice. Interestingly, MIA-resistant IL6-KO mice did not exhibit these changes. Lastly, we propose that elevated levels of the transcription factor PAX6 following MIA supports the overproduction of CTIP2⁺ neurons. Taken together, our data reveals a possible link between maternal immune activation and the excess of cortical neurons found in the cortex of ASD patients.

Maternal Infection During Pregnancy and Risk of Cerebral Palsy in Children: A Systematic Review and Meta-analysis

BACKGROUND AND AIM

The association between maternal infection during pregnancy and the risk of cerebral palsy has been previously reported. However, their results were relatively inconsistent. This systematic review and meta-analysis were carried out to investigate the association between maternal infection during pregnancy and the risk of cerebral palsy in children.

METHODS

PubMed, Scopus, and Web of Sciences databases were searched from inception to October 28, 2019. Heterogeneity was assessed using the I² value. In case of substantial heterogeneity (I² > 50%), a random effects model was applied, otherwise, a fixed effects model was used. The pooled associations were expressed as relative risks (RRs) and 95% confidence intervals (CIs). Publication bias and quality of studies included in the systematic review were checked using the Egger's regression test and Newcastle-Ottawa Scale (NOS), respectively.

RESULTS

Thirty-seven studies were included in the systematic review. Among them, 21 studies were eligible for the meta-analysis. The pooled RR of cerebral palsy risk was 2.50 (95% CI 1.94, 3.21; I² = 88.7%, P < .001) among children born to mothers who had any infection during pregnancy. The risk was increased to 2.85 (95% CI 1.96, 4.15; I² = 75.9%, P < .001) when the mother was diagnosed with chorioamnionitis. Publication bias tests suggested no evidence of potential publication bias and 76% of the studies included in the meta-analysis were of high quality (NOS ≥ 6).

CONCLUSION

This systematic review and meta-analysis provides evidence that maternal infection during pregnancy may be associated with an increased risk of cerebral palsy in children.

COVID-19 and developmental origins of health and disease

From the moment of the identification of SARS-CoV-2 as an etiological agent of the severe clinical pictures of pneumonia that were being slowly observed all over the world, numerous studies have been conducted to increase the knowledge about what was an unknown virus until then. The efforts were mainly aimed to acquire epidemiological, microbiological, pathogenetic, clinical, diagnostic, therapeutic and preventive information in order to increase the available weapons to fight an infection which was rapidly taking on the characteristics of the pandemic. Given the topicality of the problem, not everything has yet been fully understood and clarified, especially in the maternal-fetal‑neonatal field, where we are beginning to question what could be the outcomes of newborn babies born to mothers who contracted SARS-CoV-2 infection during pregnancy. Thus, the aim of this review is to analyze the long-term outcomes of this infection that could affect the offspring, regardless of a possible maternal-fetal transmission, focusing on, above all, the role of maternal immune activation and the expression of the Angiotensin-converting enzyme 2 (ACE2) in particular at the placental level.

Prenatal and perinatal metabolic risk factors for autism: a review and integration of findings from population-based studies

PURPOSE OF REVIEW

Given the ongoing rise in prevalence of autism spectrum disorder (ASD) and the challenges in developing and administering interventions to significantly alleviate ASD symptoms, there is an urgent need to identify modifiable risk factors for ASD. The goal of this review is to systematically evaluate the current evidence for an association between conditions related to maternal metabolic syndrome and risk for ASD in offspring focusing on methodically rigorous studies.

RECENT FINDINGS

In recent years, multiple studies explored the association between various conditions related to maternal metabolic syndrome (obesity, hypertension, or diabetes prior to, or with onset during pregnancy) and ASD risk in the offspring.

SUMMARY

Examining large, sufficiently powered, population-based epidemiological studies that explored the association between maternal metabolic syndrome and ASD, we found consistent evidence for an association between maternal preeclampsia and risk for ASD. Other conditions that are part of maternal metabolic syndrome, including maternal obesity, gestational weight gain, diabetes and gestational diabetes, should be studied further with careful attention paid to potential synergistic effects between different metabolic conditions. These findings highlight the need for rigorous, large, population-based epidemiological studies of potentially modifiable ASD risk factors that could inform public health interventions.

Gastrointestinal Issues and Autism Spectrum Disorder

Gastrointestinal disorders are one of the most common medical conditions that are comorbid with autism spectrum disorders. These comorbidities can cause greater severity in autism spectrum disorder symptoms, other associated clinical manifestations, and lower quality of life if left untreated. Clinicians need to understand how these gastrointestinal issues present and apply effective therapies. Effective treatment of gastrointestinal problems in autism spectrum disorder may result in marked improvements in autism spectrum disorder behavioral outcomes. This article discusses the gastrointestinal disorders commonly associated with autism spectrum disorders, how they present, and studied risk factors.

Maternal immune responses and obstetrical outcomes of pregnant women with COVID-19 and possible health risks of offspring

Coronavirus disease 2019 (COVID-19) pandemic has spread rapidly across the world. The vast majority of patients with COVID-19 manifest mild to moderate symptoms but may progress to severe cases or even mortalities. Young adults of reproductive age are the most affected population by SARS-CoV-2 infection. However, there is no consensus yet if pregnancy contributes to the severity of COVID-19. Initial studies of pregnant women have found that COVID-19 significantly increases the risk of preterm birth, intrauterine growth restriction, and low birth weight, which have been associated with non-communicable diseases in offspring. Besides, maternal viral infections with or without vertical transmission have been allied with neurological and behavioral disorders of the offspring. In this review, obstetrical outcomes of women with COVID-19 and possible risks for their offspring are discussed by reviewing maternal immune responses to COVID-19 based on the current evidence. Structural and systemic follow-up of offspring who are exposed to SARS-CoV-2 in-utero is suggested.

Preeclampsia and Neurodevelopmental Outcomes: Potential Pathogenic Roles for Inflammation and Oxidative Stress?

Preeclampsia (PE) is a common and serious hypertensive disorder of pregnancy that occurs in approximately 3-5% of first-time pregnancies and is a well-known leading cause of maternal and neonatal mortality and morbidity. In recent years, there has been accumulating evidence that in utero exposure to PE acts as an environmental risk factor for various neurodevelopmental disorders, particularly autism spectrum disorder and ADHD. At present, the mechanism(s) mediating this relationship are uncertain. In this review, we outline the most recent evidence implicating a causal role for PE exposure in the aetiology of various neurodevelopmental disorders and provide a novel interpretation of neuroanatomical alterations in PE-exposed offspring and how these relate to their sub-optimal neurodevelopmental trajectory. We then postulate that inflammation and oxidative stress, two prominent features of the pathophysiology of PE, are likely to play a major role in mediating this association. The increased inflammation in the maternal circulation, placenta and fetal circulation in PE expose the offspring to both prenatal maternal immune activation-a risk factor for neurodevelopmental disorders, which has been well-characterised in animal models-and directly higher concentrations of pro-inflammatory cytokines, which adversely affect neuronal development. Similarly, the exaggerated oxidative stress in the mother, placenta and foetus induces the placenta to secrete factors deleterious to neurons, and exposes the fetal brain to directly elevated oxidative stress and thus adversely affects neurodevelopmental processes. Finally, we describe the interplay between inflammation and oxidative stress in PE, and how both systems interact to potentially alter neurodevelopmental trajectory in exposed offspring.

Maternal acute and chronic inflammation in pregnancy is associated with common neurodevelopmental disorders: a systematic review

Inflammation is increasingly recognized as a cause or consequence of common problems of humanity including obesity, stress, depression, pollution and disease states such as autoimmunity, asthma, and infection. Maternal immune activation (MIA), triggered by both acute and systemic chronic inflammation, is hypothesized to be one of the mechanisms implicated in the pathogenesis of neurodevelopmental disorders (NDD). Although there is substantial preclinical evidence to support the MIA hypothesis, the human evidence is disparate. We performed a systematic review on human studies examining associations between maternal inflammatory states and offspring NDDs (autism spectrum disorder- ASD, attention deficit hyperactivity disorder-ADHD, Tourette syndrome-TS). 32 meta-analyses and 26 additional individual studies were identified. Maternal states associated with ASD include obesity, gestational diabetes mellitus, pre-eclampsia, pollution, stress, depression, autoimmune diseases, and infection. Maternal states associated with ADHD include obesity, pre-eclampsia, smoking, low socioeconomic status (SES), stress, autoimmune disease, and asthma. Maternal states associated with TS include low SES, depression, and autoimmune diseases. Diverse maternal inflammatory states in pregnancy are associated with common offspring NDDs. Given the increased prevalence of NDDs, there is urgent need to explore relative and cumulative maternal risk factors and disease mechanisms. Defining preventable risk factors in high-risk pregnancies could mitigate the expression and severity of NDDs.

Impact of maternal immune activation on dendritic spine development

Dendritic spines are small dendritic protrusions that harbor most excitatory synapses in the brain. The proper generation and maturation of dendritic spines are crucial for the regulation of synaptic transmission and formation of neuronal circuits. Abnormalities in dendritic spine density and morphology are common pathologies in autism and schizophrenia. According to epidemiological studies, one risk factor for these neurodevelopmental disorders is maternal infection during pregnancy. This review discusses spine alterations in animal models of maternal immune activation in the context of neurodevelopmental disorders. We describe potential mechanisms that might be responsible for prenatal infection-induced changes in the dendritic spine phenotype and behavior in offspring.

NOX1/NADPH oxidase affects the development of autism-like behaviors in a maternal immune activation model

Autism spectrum disorder (ASD) is a neurodevelopmental disorder caused by genetic and environmental factors. Among the environmental factors, maternal infection is known as one of the principal risk factors for ASD. On the other hand, postmortem studies suggested the relationship of oxidative stress with ASD etiology. However, the role of oxidative stress in the development of ASD remains unclear. Here, we report the involvement of NOX1/NADPH oxidase, an enzyme generating reactive oxygen species (ROS), in behavioral and anatomical abnormalities in a maternal immune activation (MIA) model. In the MIA model of gestational polyinosinic-polycytidylic acid (poly(I:C)) exposure, increased serum levels of IL-6 were observed in both wild-type (WT) and Nox1-deficient mice (Nox1KO). Following the comparable induction of MIA in the two genotypes, impairment of social preference and defects in motor coordination were observed in WT offspring but not in offspring deficient in Nox1. MIA up-regulated NOX1 mRNA in the cerebral cortex and cerebellum of the fetus but not in the adult offspring. Although the development of cortical neurons was unaffected by MIA in either genotype, the dropout of Purkinje cells in lobule VII of MIA-affected offspring was significantly ameliorated in Nox1KO. Taken together, these results suggested that NOX1/NADPH oxidase plays an essential role in some behavioral phenotypes observed in ASD, possibly by promoting the loss of Purkinje cells in the cerebellum.

Healing autism spectrum disorder with cannabinoids: a neuroinflammatory story

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with a multifactorial etiology. Latest researches are raising the hypothesis of a link between the onset of the main behavioral symptoms of ASD and the chronic neuroinflammatory condition of the autistic brain; increasing evidence of this connection is shedding light on new possible players in the pathogenesis of ASD. The endocannabinoid system (ECS) has a key role in neurodevelopment as well as in normal inflammatory responses and it is not surprising that many preclinical and clinical studies account for alterations of the endocannabinoid signaling in ASD. These findings lay the foundation for a better understanding of the neurochemical mechanisms underlying ASD and for new therapeutic attempts aimed at exploiting the renowned anti-inflammatory properties of cannabinoids to treat pathologies encompassed in the autistic spectrum. This review discusses the current preclinical and clinical evidence supporting a key role of the ECS in the neuroinflammatory state that characterizes ASD, providing hints to identify new biomarkers in ASD and promising therapies for the future.

Human stem cell-based models for studying autism spectrum disorder-related neuronal dysfunction

The controlled differentiation of pluripotent stem cells (PSCs) into neurons and glia offers a unique opportunity to study early stages of human central nervous system development under controlled conditions in vitro. With the advent of cell reprogramming and the possibility to generate induced pluripotent stem cells (iPSCs) from any individual in a scalable manner, these studies can be extended to a disease- and patient-specific level. Autism spectrum disorder (ASD) is considered a neurodevelopmental disorder, with substantial evidence pointing to early alterations in neurogenesis and network formation as key pathogenic drivers. For that reason, ASD represents an ideal candidate for stem cell-based disease modeling. Here, we provide a concise review on recent advances in the field of human iPSC-based modeling of syndromic and non-syndromic forms of ASD, with a particular focus on studies addressing neuronal dysfunction and altered connectivity. We further discuss recent efforts to translate stem cell-based disease modeling to 3D via brain organoid and cell transplantation approaches, which enable the investigation of disease mechanisms in a tissue-like context. Finally, we describe advanced tools facilitating the assessment of altered neuronal function, comment on the relevance of iPSC-based models for the assessment of pharmaceutical therapies and outline potential future routes in stem cell-based ASD research.