Maternal autoantibodies are associated with abnormal brain enlargement in a subgroup of children with autism spectrum disorder

Prenatal Neurogenesis in Autism Spectrum Disorders

An ever-increasing body of literature describes compelling evidence that a subset of young children on the autism spectrum show abnormal cerebral growth trajectories. In these cases, normal cerebral size at birth is followed by a period of abnormal growth and starting in late childhood often by regression compared to unaffected controls. Recent work has demonstrated an abnormal increase in the number of neurons of the prefrontal cortex suggesting that cerebral size increase in autism is driven by excess neuronal production. In addition, some affected children display patches of abnormal laminar positioning of cortical projection neurons. As both cortical projection neuron numbers and their correct layering within the developing cortex requires the undisturbed proliferation of neural progenitors, it appears that neural progenitors lie in the center of the autism pathology associated with early brain overgrowth. Consequently, autism spectrum disorders associated with cerebral enlargement should be viewed as birth defects of an early embryonic origin with profound implications for their early diagnosis, preventive strategies, and therapeutic intervention.

Autoimmunity in neuropsychiatric disorders

The immune system's role in the pathophysiology of several neuropsychiatric disorders has been the subject of research for many decades. Despite suggestive evidence from genetic, epidemiologic, and immunologic studies, those findings did not translate into clinical practice. Recent recognition of antibody-mediated central nervous system (CNS) disorders has fueled the search for a subgroup of patients with an antibody-mediated psychiatric illness. This chapter focuses on the current understanding of autoimmune CNS disorders and how they may be relevant to psychiatric disorders, particularly schizophrenia and autism. We review the results provided by antibody screening in psychiatric patient groups and discuss future directions to establish whether those findings will be meaningful in clinical practice.

Head circumference and brain size in autism spectrum disorder: A systematic review and meta-analysis

Macrocephaly and brain overgrowth have been associated with autism spectrum disorder. We performed a systematic review and meta-analysis to provide an overall estimate of effect size and statistical significance for both head circumference and total brain volume in autism. Our literature search strategy identified 261 and 391 records, respectively; 27 studies defining percentages of macrocephalic patients and 44 structural brain imaging studies providing total brain volumes for patients and controls were included in our meta-analyses. Head circumference was significantly larger in autistic compared to control individuals, with 822/5225 (15.7%) autistic individuals displaying macrocephaly. Structural brain imaging studies measuring brain volume estimated effect size. The effect size is higher in low functioning autistics compared to high functioning and ASD individuals. Brain overgrowth was recorded in 142/1558 (9.1%) autistic patients. Finally, we found a significant interaction between age and total brain volume, resulting in larger head circumference and brain size during early childhood. Our results provide conclusive effect sizes and prevalence rates for macrocephaly and brain overgrowth in autism, confirm the variation of abnormal brain growth with age, and support the inclusion of this endophenotype in multi-biomarker diagnostic panels for clinical use.

Hyperactivity and attention deficits in mice with decreased levels of stress-inducible phosphoprotein 1 (STIP1)

Stress-inducible phosphoprotein I (STIP1, STI1 or HOP) is a co-chaperone intermediating Hsp70/Hsp90 exchange of client proteins, but it can also be secreted to trigger prion protein-mediated neuronal signaling. Some mothers of children with autism spectrum disorders (ASD) present antibodies against certain brain proteins, including antibodies against STIP1. Maternal antibodies can cross the fetus blood-brain barrier during pregnancy, suggesting the possibility that they can interfere with STIP1 levels and, presumably, functions. However, it is currently unknown whether abnormal levels of STIP1 have any impact in ASD-related behavior. Here, we used mice with reduced (50%) or increased STIP1 levels (fivefold) to test for potential ASD-like phenotypes. We found that increased STIP1 regulates the abundance of Hsp70 and Hsp90, whereas reduced STIP1 does not affect Hsp70, Hsp90 or the prion protein. Interestingly, BAC transgenic mice presenting fivefold more STIP1 show no major phenotype when examined in a series of behavioral tasks, including locomotor activity, elevated plus maze, Morris water maze and five-choice serial reaction time task (5-CSRTT). In contrast, mice with reduced STIP1 levels are hyperactive and have attentional deficits on the 5-CSRTT, but exhibit normal performance for the other tasks. We conclude that reduced STIP1 levels can contribute to phenotypes related to ASD. However, future experiments are needed to define whether it is decreased chaperone capacity or impaired prion protein signaling that contributes to these phenotypes.

Summary: Here, using a series of behavioral tests including touchscreen tasks we show that decreased levels of stress-inducible phosphoprotein 1 (STIP1) lead to attention deficits and hyperactivity in mice.

Maternal Anti-Fetal Brain IgG Autoantibodies and Autism Spectrum Disorder: Current Knowledge and its Implications for Potential Therapeutics

Several studies have found a correlation between the presence of circulating maternal autoantibodies and neuronal dysfunction in the neonate. Specifically, maternal anti-brain autoantibodies, which may access the fetal compartment during gestation, have been identified as one risk factor for developing autism spectrum disorder (ASD). Studies by our laboratory elucidated seven neurodevelopmental proteins recognized by maternal autoantibodies whose presence is associated with a diagnosis of maternal autoantibody-related (MAR) autism in the child. While the specific process of anti-brain autoantibody generation is unclear and the detailed pathogenic mechanisms are currently unknown, identification of the maternal autoantibody targets increases the therapeutic possibilities. The potential therapies discussed in this review provide a framework for possible future medical interventions.

Catalytic autoantibodies against myelin basic protein (MBP) isolated from serum of autistic children impair in vitro models of synaptic plasticity in rat hippocampus

Autoantibodies from autistic spectrum disorder (ASD) patients react with multiple proteins expressed in the brain. One such autoantibody targets myelin basic protein (MBP). ASD patients have autoantibodies to MBP of both the IgG and IgA classes in high titers, but no autoantibodies of the IgM class. IgA autoantibodies act as serine proteinases and degrade MBP in vitro. They also induce a decrease in long-term potentiation in the hippocampi of rats either perfused with or previously inoculated with this IgA. Because this class of autoantibody causes myelin sheath destruction in multiple sclerosis (MS), we hypothesized a similar pathological role for them in ASD.

Preliminary findings suggest the number and volume of supragranular and infragranular pyramidal neurons are similar in the anterior superior temporal area of control subjects and subjects with autism

We investigated the cytoarchitecture of the anterior superior temporal area (TA2) of the postmortem cerebral cortex in 9 subjects with autism and 9 age-matched typically developing subjects between the ages of 13 and 56 years. The superior temporal gyrus is involved in auditory processing and social cognition and its pathology has been correlated with autism. We quantified the number and soma volume of pyramidal neurons in the supragranular layers and pyramidal neurons in the infragranular layers in each subject. We did not find significant differences in the number or volume of supragranular or infragranular neurons in the cerebral cortex of subjects with autism compared to typically developing subjects. This report does not support an alteration of supragranular to infragranular neurons in autism. However, further stereological analysis of the number of cells and cell volumes in specific cortical areas is needed to better establish the cellular phenotype of the autistic cerebral cortex and to understand its clinical relevance in autism.

Altered expression levels of neurodevelopmental proteins in fetal brains of BTBR T+tf/J mice with autism-like behavioral characteristics

Autism is a brain developmental disorder with characteristics of social interaction defects, language and communication dysfunction, and repetitive behavior. Occurrence of autism is continuously increasing, but the cause of autism is not clearly defined. Genetic linkage or environmental factors were proposed as sources for pathogenesis of autism. BTBR T+tf/J (BTBR) mice were reported as an appropriate animal model for autism investigation because of their similarities in behavioral abnormalities with human autistic subjects. The aim of this study was to evaluate expression levels of proteins involved with brain development at fetal stage of BTBR mice. FVB/NJ mice were used as a control strain because of their social behaviors. Level of fetal brain immunoglobulin (Ig) G deposit was also evaluated. Fetal brains were obtained at d 18 of gestational period. Thirty-one and 27 fetuses were obtained from 3 pregnant BTBR and FVB dams, respectively. The level of glial fibrillary acidic protein expression was significantly lower in fetal brains of BTBR than FVB/NJ mice. Expression of brain-derived neurotrophic factor and myelin basic protein was significantly more upregulated in BTBR than in FVB/NJ mice. No significant difference was obtained for nerve growth factor between the two strains. Levels of IgG isotypes deposited in fetal brain of BTBR mice were significantly higher than in FVB mice except for IgG1. Overall, these results suggest that prenatal alterations in expression of various fetal brain proteins may be implicated in aberrant behavioral characteristics of BTBR mice.

Prenatal Exposure to Autism-Specific Maternal Autoantibodies Alters Proliferation of Cortical Neural Precursor Cells, Enlarges Brain, and Increases Neuronal Size in Adult Animals

Autism spectrum disorders (ASDs) affect up to 1 in 68 children. Autism-specific autoantibodies directed against fetal brain proteins have been found exclusively in a subpopulation of mothers whose children were diagnosed with ASD or maternal autoantibody-related autism. We tested the impact of autoantibodies on brain development in mice by transferring human antigen-specific IgG directly into the cerebral ventricles of embryonic mice during cortical neurogenesis. We show that autoantibodies recognize radial glial cells during development. We also show that prenatal exposure to autism-specific maternal autoantibodies increased stem cell proliferation in the subventricular zone (SVZ) of the embryonic neocortex, increased adult brain size and weight, and increased the size of adult cortical neurons. We propose that prenatal exposure to autism-specific maternal autoantibodies directly affects radial glial cell development and presents a viable pathologic mechanism for the maternal autoantibody-related prenatal ASD risk factor.

Evidence supporting an altered immune response in ASD

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by deficits in social interactions, communication, and increased stereotypical repetitive behaviors. The immune system plays an important role in neurodevelopment, regulating neuronal proliferation, synapse formation and plasticity, as well as removing apoptotic neurons. Immune dysfunction in ASD has been repeatedly described by many research groups across the globe. Symptoms of immune dysfunction in ASD include neuroinflammation, presence of autoantibodies, increased T cell responses, and enhanced innate NK cell and monocyte immune responses. Moreover these responses are frequently associated with more impairment in core ASD features including impaired social interactions, repetitive behaviors and communication. In mouse models replacing immune components in animals that exhibit autistic relevant features leads to improvement in behavior in these animals. Taken together this research suggests that the immune dysfunction often seen in ASD directly affects aspects of neurodevelopment and neurological processes leading to changes in behavior. Discussion of immune abnormalities in ASD will be the focus of this review.

Microbiota, immunoregulatory old friends and psychiatric disorders

Regulation of the immune system is an important function of the gut microbiota. Increasing evidence suggests that modern living conditions cause the gut microbiota to deviate from the form it took during human evolution. Contributing factors include loss of helminth infections, encountering less microbial biodiversity, and modulation of the microbiota composition by diet and antibiotic use. Thus the gut microbiota is a major mediator of the hygiene hypothesis (or as we prefer, "Old Friends" mechanism), which describes the role of organisms with which we co-evolved, and that needed to be tolerated, as crucial inducers of immunoregulation. At least partly as a consequence of reduced exposure to immunoregulatory Old Friends, many but not all of which resided in the gut, high-income countries are undergoing large increases in a wide range of chronic inflammatory disorders including allergies, autoimmunity and inflammatory bowel diseases. Depression, anxiety and reduced stress resilience are comorbid with these conditions, or can occur in individuals with persistently raised circulating levels of biomarkers of inflammation in the absence of clinically apparent peripheral inflammatory disease. Moreover poorly regulated inflammation during pregnancy might contribute to brain developmental abnormalities that underlie some cases of autism spectrum disorders and schizophrenia. In this chapter we explain how the gut microbiota drives immunoregulation, how faulty immunoregulation and inflammation predispose to psychiatric disease, and how psychological stress drives further inflammation via pathways that involve the gut and microbiota. We also outline how this two-way relationship between the brain and inflammation implicates the microbiota, Old Friends and immunoregulation in the control of stress resilience.

Maternal inflammation contributes to brain overgrowth and autism-associated behaviors through altered redox signaling in stem and progenitor cells

A period of mild brain overgrowth with an unknown etiology has been identified as one of the most common phenotypes in autism. Here, we test the hypothesis that maternal inflammation during critical periods of embryonic development can cause brain overgrowth and autism-associated behaviors as a result of altered neural stem cell function. Pregnant mice treated with low-dose lipopolysaccharide at embryonic day 9 had offspring with brain overgrowth, with a more pronounced effect in PTEN heterozygotes. Exposure to maternal inflammation also enhanced NADPH oxidase (NOX)-PI3K pathway signaling, stimulated the hyperproliferation of neural stem and progenitor cells, increased forebrain microglia, and produced abnormal autism-associated behaviors in affected pups. Our evidence supports the idea that a prenatal neuroinflammatory dysregulation in neural stem cell redox signaling can act in concert with underlying genetic susceptibilities to affect cellular responses to environmentally altered cellular levels of reactive oxygen species.

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Mild maternal inflammation produces brain overgrowth and autistic behaviors in pups

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Maternal inflammation increases stem cell division, ROS levels, and PI3K activation

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Genetic susceptibility produces even greater brain overgrowth when combined with MIR

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Overgrowth and some associated abnormal behaviors can be rescued by inhibition of NOX

Early generalized overgrowth in autism spectrum disorder: prevalence rates, gender effects, and clinical outcomes

OBJECTIVE

Although early head and body overgrowth have been well documented in autism spectrum disorder (ASD), their prevalence and significance remain unclear. It is also unclear whether overgrowth affects males and females differentially, and whether it is associated with clinical outcomes later in life.

METHOD

To evaluate prevalence of somatic overgrowth, gender effects, and associations with clinical outcomes, head circumference, height, and weight measurements were collected retrospectively between birth and 2 years of age in toddlers with ASD (n = 200) and typically developing (TD; n = 147) community controls. Symptom severity, verbal, and nonverbal functioning were assessed at 4 years.

RESULTS

Abnormalities in somatic growth in infants with ASD were consistent with early generalized overgrowth (EGO). Boys but not girls with ASD were larger and exhibited an increased rate of extreme EGO compared to community controls (18.0% versus 3.4%). Presence of a larger body at birth and postnatal overgrowth were associated independently with poorer social, verbal, and nonverbal skills at 4 years.

CONCLUSION

Although early growth abnormalities in ASD are less common than previously thought, their presence is predictive of lower social, verbal, and nonverbal skills at 4 years, suggesting that they may constitute a biomarker for identifying toddlers with ASD at risk for less-optimal outcomes. The results highlight that the search for mechanisms underlying atypical brain development in ASD should consider factors responsible for both neural and nonneural tissue development during prenatal and early postnatal periods, and can be informed by the finding that early overgrowth may be more readily observed in males than in females with ASD.

Anti-brain antibodies are associated with more severe cognitive and behavioral profiles in Italian children with Autism Spectrum Disorder

Circulating 45 and 62kDa antibodies targeting the cerebellum were previously associated with Autism Spectrum Disorder (ASD), lower adaptive/cognitive function and aberrant behaviors. Moreover, 37, 39 and 73kDa maternal antibodies (mAb) targeting the fetal brain were previously correlated with broad autism spectrum, irritability, abnormal brain enlargement and impaired expressive language. The present study aims towards clinically characterizing individuals with brain-targeted IgG and/or exposed to maternal antibrain antibodies in a large sample of Italian autistic children (N=355), their unaffected siblings (N=142) and mothers (N=333). The presence of patient- and mother-produced anti-brain antibodies does not confer increased risk of autism within the same sibship. However, the 45 and 62kDa antibodies are correlated with autism severity: the 45kDa Ab is associated with cognitive impairment and lower scores at the Vineland Adaptive Behavior Scales, the 62kDa Ab with motor stereotypies, while both correlate with larger head circumference (all P<0.05). On the other hand, maternal 37, 39 and 73kDa antibrain antibodies, either alone or in combination, are correlated with impaired verbal and non-verbal language development, neurodevelopmental delay and sleep/wake cycle disturbances in their autistic children (P<0.05). Presence of the 62kDa autoAb in the child is significantly associated with presence of the 39 and/or 73kDa antibodies in his/her mother. Our results confirm and extend previous observations in an ethnically distinct sample, providing further evidence of a pathomorphic role for anti-brain antibodies in autism while demonstrating their familial clustering.

Brain autoantibodies in autism spectrum disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by impairments in reciprocal social interactions as well as restricted, repetitive and stereotyped patterns of behavior. The etiology of ASD is not well understood, although many factors have been associated with its pathogenesis, such genetic, neurological, environmental and immunological factors. Several studies have reported the production of numerous autoantibodies that react with specific brain proteins and brain tissues in autistic children and alter the function of the attacked brains tissue. In addition, the potential role of maternal autoantibodies to the fatal brain in the etiology of some cases of autism has also been reported. Identification and understanding of the role of brain autoantibodies as biological biomarkers may allow earlier detection of ASD, lead to a better understanding of the pathogenesis of ASD and have important therapeutic implications.

Vitamin D hormone regulates serotonin synthesis. Part 1: relevance for autism

Serotonin and vitamin D have been proposed to play a role in autism; however, no causal mechanism has been established. Here, we present evidence that vitamin D hormone (calcitriol) activates the transcription of the serotonin-synthesizing gene tryptophan hydroxylase 2 (TPH2) in the brain at a vitamin D response element (VDRE) and represses the transcription of TPH1 in tissues outside the blood-brain barrier at a distinct VDRE. The proposed mechanism explains 4 major characteristics associated with autism: the low concentrations of serotonin in the brain and its elevated concentrations in tissues outside the blood-brain barrier; the low concentrations of the vitamin D hormone precursor 25-hydroxyvitamin D [25(OH)D3]; the high male prevalence of autism; and the presence of maternal antibodies against fetal brain tissue. Two peptide hormones, oxytocin and vasopressin, are also associated with autism and genes encoding the oxytocin-neurophysin I preproprotein, the oxytocin receptor, and the arginine vasopressin receptor contain VDREs for activation. Supplementation with vitamin D and tryptophan is a practical and affordable solution to help prevent autism and possibly ameliorate some symptoms of the disorder.

Heterogeneity within Autism Spectrum Disorders: What have We Learned from Neuroimaging Studies?

Autism spectrum disorders (ASD) display significant heterogeneity. Although most neuroimaging studies in ASD have been designed to identify commonalities among affected individuals, rather than differences, some studies have explored variation within ASD. There have been two general types of approaches used for this in the neuroimaging literature to date: comparison of subgroups within ASD, and analyses using dimensional measures to link clinical variation to brain differences. This review focuses on structural and functional magnetic resonance imaging studies that have used these approaches to begin to explore heterogeneity between individuals with ASD. Although this type of data is yet sparse, recognition is growing of the limitations of behaviorally defined categorical diagnoses for understanding neurobiology. Study designs that are more informative regarding the sources of heterogeneity in ASD have the potential to improve our understanding of the neurobiological processes underlying ASD.

Maternal antibodies from mothers of children with autism alter brain growth and social behavior development in the rhesus monkey

Antibodies directed against fetal brain proteins of 37 and 73 kDa molecular weight are found in approximately 12% of mothers who have children with autism spectrum disorder (ASD), but not in mothers of typically developing children. This finding has raised the possibility that these immunoglobulin G (IgG) class antibodies cross the placenta during pregnancy and impact brain development, leading to one form of ASD. We evaluated the pathogenic potential of these antibodies by using a nonhuman primate model. IgG was isolated from mothers of children with ASD (IgG-ASD) and of typically developing children (IgG-CON). The purified IgG was administered to two groups of female rhesus monkeys (IgG-ASD; n=8 and IgG-CON; n=8) during the first and second trimesters of pregnancy. Another control group of pregnant monkeys (n=8) was untreated. Brain and behavioral development of the offspring were assessed for 2 years. Behavioral differences were first detected when the macaque mothers responded to their IgG-ASD offspring with heightened protectiveness during early development. As they matured, IgG-ASD offspring consistently deviated from species-typical social norms by more frequently approaching familiar peers. The increased approach was not reciprocated and did not lead to sustained social interactions. Even more striking, IgG-ASD offspring displayed inappropriate approach behavior to unfamiliar peers, clearly deviating from normal macaque social behavior. Longitudinal magnetic resonance imaging analyses revealed that male IgG-ASD offspring had enlarged brain volume compared with controls. White matter volume increases appeared to be driving the brain differences in the IgG-ASD offspring and these differences were most pronounced in the frontal lobes.

Is 'bench-to-bedside' realistic for autism? An integrative neuroscience approach

Given the prevalence and societal impact of autism spectrum disorder (ASD), there is an urgent need to develop innovative treatments that will improve core social deficits, for which there is currently no reliable pharmacological treatment, prevention or cure. Development of novel biological interventions will depend upon the successful translation of basic neuroscience research into safe and effective medicines. This article outlines steps to bring neuroscience research from 'the bench' to treatment at 'bedside', from phenotyping the disorder to animal models to patient treatment. Although these steps appear simplistic, this is a daunting challenge because of the inherent complexity of the human brain, our lack of understanding of disease neurobiology underlying ASD, and the incredible heterogeneity of the disorder. For ASD, perhaps more than any other neurological or psychiatric disorder, progress will depend on integrative multidisciplinary approaches between basic scientists from varying neuroscience disciplines and clinicians to make 'bench to bedside' treatment a reality.

Immune dysregulation in autism spectrum disorder

Autism spectrum disorder (ASD) is a highly heterogeneous disorder diagnosed based on the presence and severity of core abnormalities in social communication and repetitive behavior, yet several studies converge on immune dysregulation as a feature of ASD. Widespread alterations in immune molecules and responses are seen in the brains and periphery of ASD individuals, and early life immune disruptions are associated with ASD. This chapter discusses immune-related environmental and genetic risk factors for ASD, emphasizing population-wide studies and animal research that reveal potential mechanistic pathways involved in the development of ASD-related symptoms. It further reviews immunologic pathologies seen in ASD individuals and how such abnormalities can impact neurodevelopment and behavior. Finally, it evaluates emerging evidence for an immune contribution to the pathogenesis of ASD and a potential role for immunomodulatory effects in current treatments for ASD.