Structural, genetic, and functional signatures of disordered neuro-immunological development in autism spectrum disorder

Sex Differences in Neurodevelopmental Disorders: A Key Role for the Immune System

Sex differences are prominent defining features of neurodevelopmental disorders. Understanding the sex biases in these disorders can shed light on mechanisms leading to relative risk and resilience for the disorders, as well as more broadly advance our understanding of how sex differences may relate to brain development. The prevalence of neurodevelopmental disorders is increasing, and the two most common neurodevelopmental disorders, Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) exhibit male-biases in prevalence rates and sex differences in symptomology. While the causes of neurodevelopmental disorders and their sex differences remain to be fully understood, increasing evidence suggests that the immune system plays a critical role in shaping development. In this chapter we discuss sex differences in prevalence and symptomology of ASD and ADHD, review sexual differentiation and immune regulation of neurodevelopment, and discuss findings from human and rodent studies of immune dysregulation and perinatal immune perturbation as they relate to potential mechanisms underlying neurodevelopmental disorders. This chapter will give an overview of how understanding sex differences in neuroimmune function in the context of neurodevelopmental disorders could lend insight into their etiologies and better treatment strategies.

Autoimmune Encephalitis and Autism Spectrum Disorder

The concept of "acquired autism" refers to the hypothesis that amongst the massive heterogeneity that encompasses autism spectrum disorder (ASD) there may be several phenotypes that are neither syndromic nor innate. Strong and consistent evidence has linked exposure to various pharmacological and infective agents with an elevated risk of a diagnosis of ASD including maternal valproate use, rubella and herpes encephalitis. Autoimmune encephalitis (AE) describes a group of conditions characterised by the body's immune system mounting an attack on healthy brain cells causing brain inflammation. The resultant cognitive, psychiatric and neurological symptoms that follow AE have also included ASD or autism-like traits and states. We review the current literature on AE and ASD. Drawing also on associated literature on autoimmune psychosis (AP) and preliminary evidence of a psychosis-linked subtype of ASD, we conclude that AE may either act as a potentially causative agent for ASD, and/or produce symptoms that could easily be mistaken for or misdiagnosed as autism. Further studies are required to discern the connection between AE and autism. Where autism is accompanied by regression and atypical onset patterns, it may be prudent to investigate whether a differential diagnosis of AE would be more appropriate.

Bridging the Gap Between Physical Health and Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a highly complex and heterogeneous developmental disorder that affects how individuals communicate with other people and relate to the world around them. Research and clinical focus on the behavioural and cognitive manifestations of ASD, whilst important, have obscured the recognition that ASD is also commonly associated with a range of physical and mental health conditions. Many physical conditions appear with greater frequency in individuals with ASD compared to non-ASD populations. These can contribute to a worsening of social communication and behaviour, lower quality of life, higher morbidity and premature mortality. We highlight some of the key physical comorbidities affecting the immune and the gastrointestinal systems, metabolism and brain function in ASD. We discuss how healthcare professionals working with individuals with ASD and parents/carers have a duty to recognise their needs in order to improve their overall health and wellbeing, deliver equality in their healthcare experiences and reduce the likelihood of morbidity and early mortality associated with the condition.

An Investigation of SDF1/CXCR4 Gene Polymorphisms in Autism Spectrum Disorder: A Family-Based Study

OBJECTIVE

Autism spectrum disorders (ASD) have a complex pathophysiology including genetic, inflammatory and neurodevelopmental components. We aim to investigate the relationship between ASD and gene polymorphisms of stromal cell-derived factor-1 (SDF-1) and its receptor CXC chemokine receptor-4 (CXCR4), which may affect inflammatory and neurodevelopmental processes.

METHODS

101 children diagnosed with ASD aged 2-18 and their biological parents were included in the study. All participants were assessed using an information form and the Children were assessed using Childhood Autism Rating Scale (CARS). SDF-1 G801→A and CXCR4 C13→T polymorphisms were detected by genetic techniques. The results were evaluated using the transmission disequilibrium test (TDT) and haplotype relative risk (HRR).

RESULTS

Following TDT evaluation for CXCR4, the assumption of equality was not rejected (χ²=1.385, p=0.239). HRR for the C allele was 1.037 [HRR (95%CI)=0.937 (0.450-2.387), χ²=0.007, p=0.933] and HRR for the T allele was 0.965 [HRR (95%CI)=0.965 (0.419- 2.221), χ²=1.219, p=0.270], but the findings were statistically insignificant. Based on TDT evaluation for SDF1, the assumption of equality cannot be rejected (χ²=0, p=0.999). HRR for the A allele was 0.701 [HRR (95%CI)=0.701 (0.372-1.319), χ²=1.219, p=0.270] and HRR for the G allele was 1.427 [HRR (95%CI)=1.427 (0.758-2.686), χ²=1.219, p=0.270], but the findings were statistically insignificant.

CONCLUSION

The genetic screening of blood samples from mother, father and child trios could not show a significant association between SDF1/CXCR4 genes and ASD on the basis of TDT and HRR tests. More extensive genetic studies are now needed to investigate the relationship between SDF1/CXCR4 gene polymorphisms and ASD.

Integrative analysis of genetic data sets reveals a shared innate immune component in autism spectrum disorder and its co-morbidities

BACKGROUND

Autism spectrum disorder (ASD) is a common neurodevelopmental disorder that tends to co-occur with other diseases, including asthma, inflammatory bowel disease, infections, cerebral palsy, dilated cardiomyopathy, muscular dystrophy, and schizophrenia. However, the molecular basis of this co-occurrence, and whether it is due to a shared component that influences both pathophysiology and environmental triggering of illness, has not been elucidated. To address this, we deploy a three-tiered transcriptomic meta-analysis that functions at the gene, pathway, and disease levels across ASD and its co-morbidities.

RESULTS

Our analysis reveals a novel shared innate immune component between ASD and all but three of its co-morbidities that were examined. In particular, we find that the Toll-like receptor signaling and the chemokine signaling pathways, which are key pathways in the innate immune response, have the highest shared statistical significance. Moreover, the disease genes that overlap these two innate immunity pathways can be used to classify the cases of ASD and its co-morbidities vs. controls with at least 70 % accuracy.

CONCLUSIONS

This finding suggests that a neuropsychiatric condition and the majority of its non-brain-related co-morbidities share a dysregulated signal that serves as not only a common genetic basis for the diseases but also as a link to environmental triggers. It also raises the possibility that treatment and/or prophylaxis used for disorders of innate immunity may be successfully used for ASD patients with immune-related phenotypes.

Autism: Oxytocin, serotonin, and social reward

Over 70 years since the first description of the disease, disrupted social behavior remains a core clinical feature of autistic spectrum disorder. The complex etiology of the disorder portends the need for a better understanding of the brain mechanisms that enable social behaviors, particularly those that are relevant to autism which is characterized by a failure to develop peer relationships, difficulty with emotional reciprocity and imitative play, and disrupted language and communication skills. Toward this end, the current review will examine recent progress that has been made toward understanding the neural mechanisms underlying consociate social attachments.

Comparative two-dimensional polyacrylamide gel electrophoresis of the salivary proteome of children with autism spectrum disorder

In the last decades, prevalence of autism spectrum disorder (ASD) has been on the rise. However, clear aetiology is still elusive and improvements in early diagnosis are needed. To uncover possible biomarkers present in ASD, we used two-dimensional polyacrylamide gel electrophoresis and nanoliquid chromatography-tandem mass spectrometry (nanoLC-MS/MS), to compare salivary proteome profiling of children with ASD and controls. A total of 889 spots were compared and only those spots with a fold change ≥1.7 and a P-value <0.05 or a fold change of ≥3.0 between ASD cases and controls were analysed by nanoLC-MS/MS. Alpha-amylase, CREB-binding protein, p532, Transferrin, Zn alpha2 glycoprotein, Zymogen granule protein 16, cystatin D and plasminogen were down-regulated in ASD. Increased expression of proto-oncogene Frequently rearranged in advanced T-cell lymphomas 1 (FRAT1), Kinesin family member 14, Integrin alpha6 subunit, growth hormone regulated TBC protein 1, parotid secretory protein, Prolactin-inducible protein precursor, Mucin-16, Ca binding protein migration inhibitory factor-related protein 14 (MRP14) was observed in individuals with ASD. Many of the identified proteins have previously been linked to ASD or were proposed as risk factors of ASD at the genetic level. Some others are involved in pathological pathways implicated in ASD causality such as oxidative stress, lipid and cholesterol metabolism, immune system disturbances and inflammation. These data could contribute to protein signatures for ASD presence, risk and subtypes, and advance understanding of ASD cause as well as provide novel treatment targets for ASD.

Salivary proteomics and biomarkers in neurology and psychiatry

Biomarkers are greatly needed in the fields of neurology and psychiatry, to provide objective and earlier diagnoses of CNS conditions. Proteomics and other omics MS-based technologies are tools currently being utilized in much recent CNS research. Saliva is an interesting alternative biomaterial for the proteomic study of CNS disorders, with several advantages. Collection is noninvasive and saliva has many proteins. It is easier to collect than blood and can be collected by professionals without formal medical training. For psychiatric and neurological patients, supplying a saliva sample is less anxiety-provoking than providing a blood sample, and is less embarrassing than producing a urine specimen. The use of saliva as a biomaterial has been researched for the diagnosis of and greater understanding of several CNS conditions, including neurodegenerative diseases, autism, and depression. Salivary biomarkers could be used to rule out nonpsychiatric conditions that are often mistaken for psychiatric/neurological conditions, such as fibromyalgia, and potentially to assess cognitive ability in individuals with compromised brain function. As MS and omics technology advances, the sensitivity and utility of assessing CNS conditions using distal human biomaterials such as saliva is becoming increasingly possible.

"Maybe at birth there was an injury": drivers and implications of caretaker explanatory models of autistic characteristics in Kerala, India

Explanatory models (EMs) are the way people explain the presence and meaning of an illness or disability and are reliant on and reflective of culturally specific values of normalcy, disability, health, and illness. EMs about autism spectrum disorder (ASD) are particularly revealing because there is no known cause, and so people can explain this disability in ways more appropriate for and useful to them. This article presents caretaker EMs about children with autistic characteristics in Kerala, India. I argue that the reliance on biological, but not genetic, causal models is reflective of the state's high access to biomedical heath care. These EMs are used to deflect the stigma of 'bad blood' and reflect a nuanced relationship between stigma and biological EMs. Understanding how caretakers talk about ASD and related conditions is critical for anyone interested in engaging in crosscultural or international autism-related work.

Epigenetics of autism-related impairment: copy number variation and maternal infection

OBJECTIVE

Epidemiological data have suggested maternal infection and fever to be associated with increased risk of autism spectrum disorder (ASD). Animal studies show that gestational infections perturb fetal brain development and result in offspring with the core features of autism and have demonstrated that behavioral effects of maternal immune activation are dependent on genetic susceptibility. The goal of this study was to explore the impact of ASD-associated copy number variants (CNVs) and prenatal maternal infection on clinical severity of ASD within a dataset of prenatal history and complete genetic and phenotypic findings.

METHODS

We analyzed data from the Simons Simplex Collection sample including 1971 children with a diagnosis of ASD aged 4 to 18 years who underwent array comparative genomic hybridization screening. Information on infection and febrile episodes during pregnancy was collected through parent interview. ASD severity was clinically measured through parent-reported interview and questionnaires.

RESULTS

We found significant interactive effects between the presence of CNVs and maternal infection during pregnancy on autistic symptomatology, such that individuals with CNVs and history of maternal infection demonstrated increased rates of social communicative impairments and repetitive/restricted behaviors. In contrast, no significant interactions were found between presence of CNVs and prenatal infections on cognitive and adaptive functioning of individuals with ASD.

CONCLUSIONS

Our findings support a gene-environment interaction model of autism impairment, in that individuals with ASD-associated CNVs are more susceptible to the effects of maternal infection and febrile episodes in pregnancy on behavioral outcomes and suggest that these effects are specific to ASD rather than to global neurodevelopment.

A starring role for microglia in brain sex differences

Microglia, the resident innate immune cells in the brain, have long been understood to be crucial to maintenance in the nervous system, by clearing debris, monitoring for infiltration of infectious agents, and mediating the brain's inflammatory and repair response to traumatic injury, stroke, or neurodegeneration. A wave of new research has shown that microglia are also active players in many basic processes in the healthy brain, including cell proliferation, synaptic connectivity, and physiology. Microglia, both in their capacity as phagocytic cells and via secretion of many neuroactive molecules, including cytokines and growth factors, play a central role in early brain development, including sexual differentiation of the brain. In this review, we present the vast roles microglia play in normal brain development and how perturbations in the normal neuroimmune environment during development may contribute to the etiology of brain-based disorders. There are notable differences between microglia and neuroimmune signaling in the male and female brain throughout the life span, and these differences may contribute to the vast differences in the incidence of neuropsychiatric and neurological disorders between males and females.

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.