Le numéro de mars 2017 de Biological Psychiatry est consacré à l’autisme :

Neuroimmune Mechanisms in Autism Spectrum Disorder

1. A brief summary of the articles appearing in this issue of Biological Psychiatry. Biological Psychiatry ;2017 (3/1/) ;81(5):379.

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2. Careaga M, Murai T, Bauman MD. Maternal Immune Activation and Autism Spectrum Disorder : From Rodents to Nonhuman and Human Primates. Biological Psychiatry ;2017 (3/1/) ;81(5):391-401.

A subset of women who are exposed to infection during pregnancy have an increased risk of giving birth to a child who will later be diagnosed with a neurodevelopmental or neuropsychiatric disorder. Although epidemiology studies have primarily focused on the association between maternal infection and an increased risk of offspring schizophrenia, mounting evidence indicates that maternal infection may also increase the risk of autism spectrum disorder. A number of factors, including genetic susceptibility, the intensity and timing of the infection, and exposure to additional aversive postnatal events, may influence the extent to which maternal infection alters fetal brain development and which disease phenotype (autism spectrum disorder, schizophrenia, other neurodevelopmental disorders) is expressed. Preclinical animal models provide a test bed to systematically evaluate the effects of maternal infection on fetal brain development, determine the relevance to human central nervous system disorders, and to evaluate novel preventive and therapeutic strategies. Maternal immune activation models in mice, rats, and nonhuman primates suggest that the maternal immune response is the critical link between exposure to infection during pregnancy and subsequent changes in brain and behavioral development of offspring. However, differences in the type, severity, and timing of prenatal immune challenge paired with inconsistencies in behavioral phenotyping approaches have hindered the translation of preclinical results to human studies. Here we highlight the promises and limitations of the maternal immune activation model as a preclinical tool to study prenatal risk factors for autism spectrum disorder, and suggest specific changes to improve reproducibility and maximize translational potential.

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3. Careaga M, Rogers S, Hansen RL, Amaral DG, Van de Water J, Ashwood P. Immune Endophenotypes in Children With Autism Spectrum Disorder. Biological Psychiatry ;2017 (3/1/) ;81(5):434-441.

AbstractBackground Autism spectrum disorder (ASD) is characterized by social communication deficits and restricted, repetitive patterns of behavior. Varied immunological findings have been reported in children with ASD. To address the question of heterogeneity in immune responses, we sought to examine the diversity of immune profiles within a representative cohort of boys with ASD. Methods Peripheral blood mononuclear cells from male children with ASD (n = 50) and from typically developing age-matched male control subjects (n = 16) were stimulated with either lipopolysaccharide or phytohemagglutinin. Cytokine production was assessed after stimulation. The ASD study population was clustered into subgroups based on immune responses and assessed for behavioral outcomes. Results Children with ASD who had a proinflammatory profile based on lipopolysaccharide stimulation were more developmentally impaired as assessed by the Mullen Scales of Early Learning. They also had greater impairments in social affect as measured by the Autism Diagnostic Observation Schedule. These children also displayed more frequent sleep disturbances and episodes of aggression. Similarly, children with ASD and a more activated T cell cytokine profile after phytohemagglutinin stimulation were more developmentally impaired as measured by the Mullen Scales of Early Learning. Conclusions Children with ASD may be phenotypically characterized based upon their immune profile. Those showing either an innate proinflammatory response or increased T cell activation/skewing display a more impaired behavioral profile than children with noninflamed or non-T cell activated immune profiles. These data suggest that there may be several possible immune subphenotypes within the ASD population that correlate with more severe behavioral impairments.

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4. Eagleson KL, Xie Z, Levitt P. The Pleiotropic MET Receptor Network : Circuit Development and the Neural-Medical Interface of Autism. Biological Psychiatry ;2017 (3/1/) ;81(5):424-433.

People with autism spectrum disorder and other neurodevelopmental disorders (NDDs) are behaviorally and medically heterogeneous. The combination of polygenicity and gene pleiotropy—the influence of one gene on distinct phenotypes—raises questions of how specific genes and their protein products interact to contribute to NDDs. A preponderance of evidence supports developmental and pathophysiological roles for the MET receptor tyrosine kinase, a multifunctional receptor that mediates distinct biological responses depending upon cell context. MET influences neuron architecture and synapse maturation in the forebrain and regulates homeostasis in gastrointestinal and immune systems, both commonly disrupted in NDDs. Peak expression of synapse-enriched MET is conserved across rodent and primate forebrain, yet regional differences in primate neocortex are pronounced, with enrichment in circuits that participate in social information processing. A functional risk allele in the MET promoter, enriched in subgroups of children with autism spectrum disorder, reduces transcription and disrupts socially relevant neural circuits structurally and functionally. In mice, circuit-specific deletion of Met causes distinct atypical behaviors. MET activation increases dendritic complexity and nascent synapse number, but synapse maturation requires reductions in MET. MET mediates its specific biological effects through different intracellular signaling pathways and has a complex protein interactome that is enriched in autism spectrum disorder and other NDD candidates. The interactome is coregulated in developing human neocortex. We suggest that a gene as pleiotropic and highly regulated as MET, together with its interactome, is biologically relevant in normal and pathophysiological contexts, affecting central and peripheral phenotypes that contribute to NDD risk and clinical symptoms.

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5. Edmiston E, Ashwood P, Van de Water J. Autoimmunity, Autoantibodies, and Autism Spectrum Disorder. Biological Psychiatry ;2017 (3/1/) ;81(5):383-390.

Auism spectrum disorder (ASD) now affects one in 68 births in the United States and is the fastest growing neurodevelopmental disability worldwide. Alarmingly, for the majority of cases, the causes of ASD are largely unknown, but it is becoming increasingly accepted that ASD is no longer defined simply as a behavioral disorder, but rather as a highly complex and heterogeneous biological disorder. Although research has focused on the identification of genetic abnormalities, emerging studies increasingly suggest that immune dysfunction is a viable risk factor contributing to the neurodevelopmental deficits observed in ASD. This review summarizes the investigations implicating autoimmunity and autoantibodies in ASD.

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6. Frans EM. The Importance of Immune System Diseases in the Etiology of Attention-Deficit/Hyperactivity Disorder. Biological Psychiatry ;2017 (3/1/) ;81(5):e39-e40.

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7. Ho P, Ross DA. More Than a Gut Feeling : The Implications of the Gut Microbiota in Psychiatry. Biological Psychiatry ;2017 (3/1/) ;81(5):e35-e37.

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8. Instanes JT, Halmøy A, Engeland A, Haavik J, Furu K, Klungsøyr K. Attention-Deficit/Hyperactivity Disorder in Offspring of Mothers With Inflammatory and Immune System Diseases. Biological Psychiatry ;2017 (3/1/) ;81(5):452-459.

AbstractBackground Prenatal inflammatory mechanisms may play a role in the pathogenesis of psychiatric disorders and could be relevant for attention-deficit/hyperactivity disorder (ADHD). We investigated maternal chronic somatic diseases with immune components as possible risk factors for ADHD in offspring. Methods We performed a population-based nested case-control study by linking data from longitudinal Norwegian registers. We included all individuals born during the period 1967–2008 and alive at record linkage (2012). Individuals receiving ADHD medication during the years 2004–2012 were defined as patients with ADHD (N = 47,944), and all remaining individuals (N = 2,274,713) were defined as control subjects. The associations between maternal diseases and ADHD in offspring were analyzed using logistic regression models. Results The following chronic diseases with immune components were related to ADHD in offspring : multiple sclerosis (adjusted odds ratio [OR] = 1.8 ; 95% confidence interval [CI] = 1.2–2.5), rheumatoid arthritis (adjusted OR = 1.7 ; 95% CI = 1.5–1.9), type 1 diabetes (adjusted OR = 1.6 ; 95% CI = 1.3–2.0), asthma (adjusted OR = 1.5 ; 95% CI = 1.4–1.6), and hypothyroidism (adjusted OR = 1.2 ; 95% CI = 1.1–1.4). In contrast, chronic hypertension and type 2 diabetes showed no significant associations. Estimates were almost unchanged with additional adjustment for parental ADHD, infant birth weight, and gestational age. Although point estimates for male and female offspring were different for some diseases (e.g., maternal asthma [adjusted OR = 1.7 ; 95% CI = 1.5–1.8 for female offspring and adjusted OR = 1.5 ; 95% CI = 1.4–1.6 for male offspring]), none of the associations differed significantly by offspring sex. Conclusions Several maternal somatic diseases with immune components were found to increase the risk of ADHD in offspring. The associations could involve several causal pathways, including common genetic predisposition and environmental factors, and increased insight into the mechanisms behind these relationships could enhance our understanding of the etiology of ADHD.

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9. Krakowiak P, Goines PE, Tancredi DJ, Ashwood P, Hansen RL, Hertz-Picciotto I, Van de Water J. Neonatal Cytokine Profiles Associated With Autism Spectrum Disorder. Biological Psychiatry ;2017 (3/1/) ;81(5):442-451.

AbstractBackground Autism spectrum disorder (ASD) is a complex neurodevelopmental condition that can be reliably diagnosed at age 24 months. Immunological phenomena, including skewed cytokine production, have been observed among children with ASD. Little is known about whether immune dysregulation is present before diagnosis of ASD. Methods We examined neonatal blood spots from 214 children with ASD (141 severe, 73 mild/moderate), 62 children with typical development, and 27 children with developmental delay as control subjects who participated in the Childhood Autism Risks from Genetics and the Environment study, a population-based case-control study. Levels of 17 cytokines and chemokines were compared across groups and in relation to developmental and behavioral domains. Results Interleukin (IL)-1β and IL-4 were independently associated with ASD compared with typical development, although these relationships varied by ASD symptom intensity. Elevated IL-4 was associated with increased odds of severe ASD (odds ratio [OR] = 1.40, 95% confidence interval [CI], 1.03, 1.91), whereas IL-1β was associated with increased odds of mild/moderate ASD (OR = 3.02, 95% CI, 1.43, 6.38). Additionally, IL-4 was associated with a higher likelihood of severe ASD versus mild/moderate ASD (OR = 1.35, 95% CI, 1.04, 1.75). In male subjects with ASD, IL-4 was negatively associated with nonverbal cognitive ability (β = −3.63, SE = 1.33, p = .04). Conclusions This study is part of a growing effort to identify early biological markers for ASD. We demonstrate that peripheral cytokine profiles at birth are associated with ASD later in childhood and that cytokine profiles vary depending on ASD severity. Cytokines have complex roles in neurodevelopment, and dysregulated levels may be indicative of genetic differences and environmental exposures or their interactions that relate to ASD.

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10. McAllister AK. Immune Contributions to Cause and Effect in Autism Spectrum Disorder. Biological Psychiatry ;2017 (3/1/) ;81(5):380-382.

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11. McCarthy MM, Wright CL. Convergence of Sex Differences and the Neuroimmune System in Autism Spectrum Disorder. Biological Psychiatry ;2017 (3/1/) ;81(5):402-410.

The male bias in autism spectrum disorder incidence is among the most extreme of all neuropsychiatric disorders, yet the origins of the sex difference remain obscure. Developmentally, males are exposed to high levels of testosterone and its byproduct, estradiol. Together these steroids modify the course of brain development by altering neurogenesis, cell death, migration, differentiation, dendritic and axonal growth, synaptogenesis, and synaptic pruning, all of which can be deleteriously impacted during the course of developmental neuropsychiatric disorders. Elucidating the cellular mechanisms by which steroids modulate brain development provides valuable insights into how these processes may go awry. An emerging theme is the role of inflammatory signaling molecules and the innate immune system in directing brain masculinization, the evidence for which we review here. Evidence is also emerging that the neuroimmune system is overactivated in individuals with autism spectrum disorder. These combined observations lead us to propose that the natural process of brain masculinization puts males at risk by moving them closer to a vulnerability threshold that could more easily be breached by inflammation during critical periods of brain development. Two brain regions are highlighted : the preoptic area and the cerebellum. Both are developmentally regulated by the inflammatory prostaglandin E2, but in different ways. Microglia, innate immune cells of the brain, and astrocytes are also critical contributors to masculinization and illustrate the importance of nonneuronal cells to the health of the developing brain.

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12. Vuong HE, Hsiao EY. Emerging Roles for the Gut Microbiome in Autism Spectrum Disorder. Biological Psychiatry ;2017 (3/1/) ;81(5):411-423.

Autism spectrum disorder (ASD) is a serious neurodevelopmental disorder that affects one in 45 children in the United States, with a similarly striking prevalence in countries around the world. However, mechanisms underlying its etiology and manifestations remain poorly understood. Although ASD is diagnosed based on the presence and severity of impaired social communication and repetitive behavior, immune dysregulation and gastrointestinal issues are common comorbidities. The microbiome is an integral part of human physiology ; recent studies show that changes in the gut microbiota can modulate gastrointestinal physiology, immune function, and even behavior. Links between particular bacteria from the indigenous gut microbiota and phenotypes relevant to ASD raise the important question of whether microbial dysbiosis plays a role in the development or presentation of ASD symptoms. Here we review reports of microbial dysbiosis in ASD. We further discuss potential effects of the microbiota on ASD-associated symptoms, drawing on signaling mechanisms for reciprocal interactions among the microbiota, immunity, gut function, and behavior. In addition, we discuss recent findings supporting a role for the microbiome as an interface between environmental and genetic risk factors that are associated with ASD. These studies highlight the integration of pathways across multiple body systems that together can impact brain and behavior and suggest that changes in the microbiome may contribute to symptoms of neurodevelopmental disease.

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