Environmental factors associated with autism spectrum disorder: a scoping review for the years 2003-2013

Indian ASD probands with 25(OH)D and vitamin D binding protein deficiency exhibited higher severity

The severity of autism spectrum disorder (ASD) shows wide variations, though the reason remains unclear. Vitamin D (VitD) deficiency is considered a risk factor for ASD and its supplementation was reported to reduce symptom severity. Since VitD, either synthesized in the skin or absorbed from the food, is transported to the liver by the vitamin D binding protein (DBP), we have analyzed DBP genetic polymorphisms [rs7041 (A/C), rs4588 (G/T), and rs3755967 (C/T)] affecting DBP function [Case = 411; Control = 397], levels of plasma 25(OH)D and DBP [Case = 25; Control = 26], and DBP mRNA expression [Case = 74; Control = 44] in a group of Indo-Caucasoid ASD probands and neurotypical subjects. ASD probands with rs7041'CC', rs4588 'TT', and rs3755967 'TT' genotypes exhibited higher scores for a few traits. Scores for Imitation and Listening response were also higher in the presence of the "A-T" haplotype (rs7041-rs4588). Plasma 25(OH)D and DBP levels as well as DBP mRNA expressions were significantly lower in the ASD probands as compared to the neurotypical subjects. We infer that DBP deficiency, in the presence of risk genetic variants, could be one of the reasons for the reported 25(OH)D deficiency of the ASD probands.

Lead contamination in human milk affects infants' language trajectory: results from a prospective cohort study

Infants growing up in low- and middle-income countries are at increased risk of suffering adverse childhood experiences, including exposure to environmental pollution and lack of cognitive stimulation. In this study, we aimed to examine the levels of metals in the human milk of women living in São Paulo City, Brazil, and determine the effects on infants' neurodevelopment. For such, a total of 185 human milk samples were analyzed for arsenic (As), lead (Pb), mercury (Hg), and cadmium (Cd) using inductively coupled plasma mass spectrometry (ICP-MS). We applied the Bayley scales of infant and toddler development Third Edition (Bayley-III) to assess developmental milestones. In our analysis, we found a mean (standard deviation) concentration of As in human milk equal to 2.76 (4.09) μg L-1, followed by Pb 2.09 (5.36) and Hg 1.96 (6.68). Cd was not detected. We observed that infants exposed to Pb presented language trajectories lower than non-exposed infants (β = -0.413; 95% CI -0.653, -0.173) after adjustment for infant age, maternal education, socioeconomic status, infant sex, and sample weights. Our results report As, Pb, and Hg contamination in human milk, and that infant exposure to Pb decreased infants' language development. These results evidence maternal-child environmental exposure and its detrimental impact on infants' health.

Mesenchymal Stem Cells and Purinergic Signaling in Autism Spectrum Disorder: Bridging the Gap between Cell-Based Strategies and Neuro-Immune Modulation

The prevalence of autism spectrum disorder (ASD) is still increasing, which means that this neurodevelopmental lifelong pathology requires special scientific attention and efforts focused on developing novel therapeutic approaches. It has become increasingly evident that neuroinflammation and dysregulation of neuro-immune cross-talk are specific hallmarks of ASD, offering the possibility to treat these disorders by factors modulating neuro-immunological interactions. Mesenchymal stem cell-based therapy has already been postulated as one of the therapeutic approaches for ASD; however, less is known about the molecular mechanisms of stem cell influence. One of the possibilities, although still underestimated, is the paracrine purinergic activity of MSCs, by which stem cells ameliorate inflammatory reactions. Modulation of adenosine signaling may help restore neurotransmitter balance, reduce neuroinflammation, and improve overall brain function in individuals with ASD. In our review article, we present a novel insight into purinergic signaling, including but not limited to the adenosinergic pathway and its role in neuroinflammation and neuro-immune cross-talk modulation. We anticipate that by achieving a greater understanding of the purinergic signaling contribution to ASD and related disorders, novel therapeutic strategies may be devised for patients with autism in the near future.

The Association between Autism Spectrum Disorder and Precocious Puberty: Considering Effect Modification by Sex and Neuropsychiatric Comorbidities

Limited knowledge is available about the association between autistic spectrum disorder (ASD) and precocious puberty. Our study examined the association between the two medical conditions and effect modification by sex and neuropsychiatric comorbidities in a nationwide population. To compare the risk of precocious puberty between ASD and non-ASD cases, we conducted a Cox regression analysis using ASD as the exposure and time to precocious puberty as the outcome. We adjusted for sex, attention-deficit/hyperactivity disorder (ADHD), tic disorder, obsessive-compulsive disorder (OCD), anxiety disorder, intellectual disability, and epilepsy. We performed a moderation analysis to examine the potential moderating effects of sex and comorbidities. Patients with ASD were prone to have precocious puberty, with an adjusted hazard ratio (aHR) of 1.80 (95% CI: 1.61-2.01). For effect modification, sex, specifically females, moderated the association between ASD and precocious puberty, with a relative excess risk due to interaction (RERI) of 7.35 (95% CI 4.90-9.80). No significant effect modification was found for any of the comorbidities within the scope of additive effect modification. We found that patients with ASD were prone to precocious puberty, regardless of sex or comorbid neuropsychiatric disorders. Girls with ASD are at a particularly higher risk of developing precocious puberty.

Maternal autoimmune disease and risk of offspring autism spectrum disorder - a nationwide population-based cohort study

Introduction

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders which cause long term social and behavior impairment, and its prevalence is on the rise. Studies about the association between maternal autoimmune diseases and offspring ASD have controversial results. The aim of this study was to investigate whether maternal autoimmune diseases increase the risk of ASD in offspring from a population-based perspective.

Methods

The data sources were Taiwan's National Health Insurance Research Database (NHIRD) and Taiwan's Maternal and Child Health Database (MCHD), which were integrated and used to identify newborns whose mothers were diagnosed with autoimmune disease. Newborns were matched by maternal age, neonatal gender, and date of birth with controls whose mothers were without autoimmune disease using a ratio of 1:4 between 2004 and 2019. Data on diagnoses of autoimmune disease and autism spectrum disorders were retrieved from NHIRD. Patients who had at least 3 outpatient visits or at least 1 admission with a diagnosis of autoimmune disease and autism spectrum disorders were defined as incidence cases. The risks of ASD in offspring were compared between mothers with or without autoimmune disorders.

Results

We identified 20,865 newborns whose mothers had been diagnosed with autoimmune disease before pregnancy and matched them at a ratio of 1:4 with a total of 83,460 newborn whose mothers were without autoimmune disease, by maternal age, neonatal gender, and date of birth. They were randomly selected as the control group. The cumulative incidence rates of autism spectrum disorders (ASD) were significantly higher among the offspring of mothers with autoimmune diseases. After adjusting for cofactors, the risk of ASD remained significantly higher in children whose mother had autoimmune diseases. Regarding to specific maternal autoimmune disease, Sjögren's syndrome and rheumatoid arthritis were both associated with elevated risks of ASD in offspring.

Conclusion

Mother with autoimmune disease might be associated with increasing the risk of autism spectrum disorder in offspring.

Assessment of vulnerability dimensions considering Family History and environmental interplay in Autism Spectrum Disorder

BACKGROUND

Despite previous studies have recently shown Autism Spectrum Disorders (ASD) as having a strong genetics background, over a minimum environmental background, no study up to date has investigated the interplay between genetics and environment.

METHODS

We have collected data regarding Family History (FH) and Environmental Factors (EF) from 2,141 individuals with ASD and their caretakers throughout Brazil, based on an online questionnaire. Most of the ASD individuals were males (81%) and the average age was 02 years minimum for males and females, and the maximum age was 41 years for males and 54 for females. People from all states in Brazil have answered the questionnaire. Genetic inheritance was obtained based on the declared FH of Psychiatric and Neurological diagnosis. As for EF, exposure to risk factors during pregnancy was considered, like infections, diabetes, drugs/chemicals exposure, socioeconomic, and psychological factors. Respondents were invited to answer the questionnaire in lectures given throughout Brazil, and by the social networks of the NGO "The Tooth Fairy Project". A Multiple Correspondence Analysis (MCA) was conducted to search vulnerability dimensions, and a Cluster Analysis was conducted to classify and identify the subgroups.

RESULTS

Regarding EF, social and psychological exposures contributed to the first two dimensions. Concerning FH, the first dimension represented psychiatric FH, while the second represented neurological FH. When analyzed together, EF and FH contributed to two new dimensions: 1. psychiatric FH, and 2. a psychosocial component. Using Cluster Analysis, it was not possible to isolate subgroups by genetic vulnerability or environmental exposure. Instead, a gradient of psychiatric FH with similar contributions of EF was observed.

CONCLUSION

In this study, it was not possible to isolate groups of patients that correspond to only one component, but rather a continuum with different compositions of genetic and environmental interplay.

Relationships between Women's and Men's Modifiable Preconception Risks and Health Behaviors and Maternal and Offspring Health Outcomes: An Umbrella Review

Parental health before conception effects maternal and offspring health outcomes. Preconception care provides healthcare to prospective parents addressing modifiable preconception risks and health behaviors. This umbrella review aimed to consolidate evidence on women's and men's modifiable preconception risks or health behaviors associated with maternal and offspring health outcomes. MEDLINE, EMBASE, Maternity and Infant Care, CINAHL, and PsycINFO were searched from March 4, 2010, to March 4, 2020. Eligible studies were systematic reviews or meta-analyses of observational studies examining associations between modifiable preconception risks or health behaviors and maternal and offspring health outcomes. Screening, data extraction, and methodological quality assessment (AMSTAR 2) occurred independently by two reviewers. Degree of overlap was examined. Findings were summarized for evidence synthesis. Twenty-seven systematic reviews were included. Modifiable preconception risks and health behaviors were identified across categories: body composition (e.g., overweight, obesity), lifestyle behaviors (e.g., caffeine, smoking), nutrition (e.g., micronutrients), environmental exposures (e.g., radiation), and birth spacing (e.g., short interpregnancy intervals). Outcomes associated with exposures affected embryo (e.g., embryonic growth), maternal (e.g., gestational diabetes mellitus), fetal/neonate (e.g., preterm birth), and child (e.g., neurocognitive disorders) health. For real-world practice and policy relevance, evidence-based indicators for preconception care should include body composition, lifestyle, nutrition, environmental, and birth spacing.

Migration modulates the prevalence of ASD and ADHD: a systematic review and meta-analysis

BACKGROUND

Migration has been implicated as a risk factor for autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD), but evidence is still limited and inconsistent. We aim to investigate the relationship between migration status and risk of ASD and ADHD.

METHODS

Electronic databases including PubMed, EMBASE, Web of Science, and PsychINFO were searched to identify observational studies on this topic, from inception to February 2021. Random-effects meta-analysis models were used to pool the summary odds ratio (OR) and 95% confidence interval (95% CI), and subgroup analyses were conducted to detect possible discrepancies in associations. Certainty of evidence was assessed as per the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) guidelines.

RESULTS

A total of 13 studies (6,532,546 participants) for ASD, five studies (2,875,070 participants) for ADHD, and six studies (31,158 participants) for hyperactivity were included. Overall, the pooled results indicated that migration was associated with increased risk of ASD (pooled OR: 1.32; 95% CI: 1.07-1.63; P for Z test = 0.010), but no association was found between migration and ADHD (pooled OR: 0.84; 95% CI: 0.53-1.32; P for Z test = 0.452) or hyperactivity (pooled standardized mean difference: -0.073; 95% CIs: - 0.383-0.236; P for Z test = 0.642). Subgroup analyses further demonstrated that maternal migration was ASD risk factor (pooled OR: 1.49; 95% CI: 1.19-1.87), and migrant children were more likely to develop ASD with comorbid intellectual disability (ID) (pooled OR: 1.21, P for interaction = 0.006) than ASD without ID. After standardized the origin of migrants, European migrant children from Americas were at higher risk of ASD and ADHD (pooled OR were 4.13 and 1.26), and increased ASD risk was also observed in African children (pooled OR: 2.72). The GRADE of evidence was very low.

CONCLUSIONS

Maternal migration is a risk factor for ASD, and migrant ASD children are more likely comorbid ID. The role of migration on ADHD remains controversial, more studies are needed to assess the association between migration status and ADHD. Health care practitioners should consider screening and providing extra resources for migrant children.

Gestational Age in Autistic Children and Adolescents: Prevalence and Effects on Autism Phenotype

Pre- and post-term children show increased autism risk. Little is known about gestational age (GA) prevalence among autistic children, and their respective autism phenotype. We compared prevalence of pre-, full- and post-term birth between a population-derived sample of N = 606 (137 females, 22.61%) autistic children and adolescents (mean age = 14.01, SD = 3.63, range 3–24) from the Netherlands Autism Register, and matched controls from the Dutch birth register. Autism phenotype and comorbid symptoms were assessed with the AQ-short and SDQ questionnaires. Using logistic regression, we found higher prevalence of pre- and post-term birth among autistic individuals but no phenotypical differences across GA groups. Autism risk was particularly elevated for post-term children, highlighting the need for closer investigation of autism on the whole GA range.

Missing from the Narrative: A Seven-Decade Scoping Review of the Inclusion of Black Autistic Women and Girls in Autism Research

The intersectional experiences of Black autistic women and girls (BAWG) are missing from medical and educational research on autism spectrum disorder (ASD). Understanding the intersectional experiences of BAWG is important due to the rising prevalence of autism in Black children and girls (Centers for Disease Control and Prevention (CDC), 2020) and the concurrent lack of availability of culturally relevant autism-related interventions (Maenner et al., 2020; West et al., 2016). Intersectionality is the study of the overlapping discrimination produced by systems of oppression (Collins, 2019; Crenshaw, 1989, 1991) and allows the researcher to simultaneously address race and disability in special education (Artiles, 2013). In this scoping review, the authors used the PRISMA-ScR checklist (Tricco et al., 2018) and Arskey and O'Malley's (2005) framework to investigate the degree to which autism-related research (ARR) has included the intersectional experiences of BAWG. Utilizing narrative synthesis, strengths and gaps across the current body of literature are identified in order to set new directions for intersectional ARR. Overall, the authors found that across a 77-year period, three studies foregrounded BAWG and none addressed intersectionality as measured through criteria advanced by García and Ortiz (2013). These results reveal the scholarly neglect BAWG face in ARR, discourse, policy, and practice. A future agenda including research, practice, and policy priorities is identified and discussed.

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.

Review: Vaccine Myth-Buster - Cleaning Up With Prejudices and Dangerous Misinformation

Although vaccines have already saved and will continue to save millions of lives, they are under attack. Vaccine safety is the main target of criticism. The rapid distribution of false information, or even conspiracy theories on the internet has tremendously favored vaccine hesitancy. The World Health Organization (WHO) named vaccine hesitancy one of the top ten threats to global health in 2019. Parents and patients have several concerns about vaccine safety, of which the ubiquitous anxieties include inactivating agents, adjuvants, preservatives, or new technologies such as genetic vaccines. In general, increasing doubts concerning side effects have been observed, which may lead to an increasing mistrust of scientific results and thus, the scientific method. Hence, this review targets five topics concerning vaccines and reviews current scientific publications in order to summarize the available information refuting conspiracy theories and myths about vaccination. The topics have been selected based on the author's personal perception of the most frequently occurring safety controversies: the inactivation agent formaldehyde, the adjuvant aluminum, the preservative mercury, the mistakenly-drawn correlation between vaccines and autism and genetic vaccines. The scientific literature shows that vaccine safety is constantly studied. Furthermore, the literature does not support the allegations that vaccines may cause a serious threat to general human life. The author suggests that more researchers explaining their research ideas, methods and results publicly could strengthen the general confidence in science. In general, vaccines present one of the safest and most cost-effective medications and none of the targeted topics raised serious health concerns.

Involvement of myocyte enhancer factor 2c in the pathogenesis of autism spectrum disorder

Myocyte enhancer factor 2 (MEF2), a family of transcription factor of MADS (minichromosome maintenance 1, agamous, deficiens and serum response factor)-box family needed in the growth and differentiation of a variety of human cells, such as neural, immune, endothelial, and muscles. As per existing literature, MEF2 transcription factors have also been associated with synaptic plasticity, the developmental mechanisms governing memory and learning, and several neurologic conditions, like autism spectrum disorders (ASDs). Recent genomic findings have ascertained a link between MEF2 defects, particularly in the MEF2C isoform and the ASD. In this review, we summarized a concise overview of the general regulation, structure and functional roles of the MEF2C transcription factor. We further outlined the potential role of MEF2C as a risk factor for various neurodevelopmental disorders, such as ASD, MEF2C Haploinsufficiency Syndrome and Fragile X syndrome.

Sex differences in adult social, cognitive, and affective behavioral deficits following neonatal phlebotomy-induced anemia in mice

INTRODUCTION

Anemia is common in prematurely born infants due to blood loss resulting from frequent phlebotomies and may contribute to their neurobehavioral deficits. Preclinical models of phlebotomy-induced anemia (PIA) have revealed metabolic and genomic changes in multiple brain structures of young mice, yet the impact of neonatal PIA on early-life and adult behavior has not been assessed.

METHODS

The present study employed a range of behavioral measures in phlebotomized anemic neonatal mice to investigate short- and long-term neurodevelopmental effects. PIA from postnatal (P) days 3 to 14 caused sex-specific changes in social behavior, novelty preference, and anxiety at P17 that persisted into adulthood.

RESULTS

Our preclinical model suggests that PIA may contribute to acute and long-term behavioral and affective deficits and warrants further substantiation of the observed behavioral phenomena in larger samples.

CONCLUSIONS

We conclude that this model is a useful tool for beginning to better understand the lasting effect that early-life PIA might have on the developing brain. The differential impact of PIA on male and female subjects warrants further exploration for the development of appropriately targeted interventions.

Examining factors related to the age of diagnosis of children with autism spectrum disorder from immigrant and non-immigrant backgrounds in a diverse clinical sample

A timely diagnosis of autism spectrum disorder (ASD) is important for children as that may help inform the best services and supports needed for optimal outcomes. However, disparities in the identification of ASD have been consistently documented for racial/ethnic minority and immigrant populations. The majority of studies of immigrant populations have focused on the qualitative experience of ASD, however, greater knowledge about the predictors of the age of initial ASD diagnosis is needed. This study examined the child, maternal, and family-level factors that predicted the age of initial ASD diagnosis in a diverse clinical sample through a retrospective medical record review. Medical records of clinical evaluations conducted between 2004 and 2014 were reviewed for children with ASD born to immigrant and non-immigrant mothers. Regression analyses found that for both groups of children with ASD, using verbal language to communicate and having another diagnosis (attention-deficit/hyperactivity disorder or another condition) predicted an older age of initial ASD diagnosis. For children with ASD born to immigrant mothers, residing in a multilingual household was associated with a younger age of diagnosis. These results highlight the complexities of an ASD diagnosis among diverse children and families, particularly among immigrant communities. LAY SUMMARY: This research looked at predictors of when children received their first autism spectrum disorder diagnosis across children born to immigrant mothers and children born to U.S.-born mothers. Living in a multilingual home was related to a younger age of diagnosis for children of immigrant mothers; being verbal and having another diagnosis was related to an older age of diagnosis for both groups of children. This highlights the need to improve diagnostic services for diverse children.

Autism Spectrum and Other Neurodevelopmental Disorders in Children of Immigrants: A Brief Review of Current Evidence and Implications for Clinical Practice

Children of immigrants may have higher neurodevelopmental risks than those of non-immigrant populations. Yet, some evidence suggests that this group may receive late diagnosis, and therefore miss beneficial early interventions. Clinicians may misattribute symptoms of disorders to other social, behavioral or language problems. Likewise, there might be cultural differences in parents' likelihood of perceiving or reporting first developmental concerns to clinicians. Population-based standardized screening may play an important role in addressing ethnic inequalities in the age at diagnosis, although further research focusing on cross-cultural use is necessary. Once children are diagnosed, clinicians may rely on culturally sensitive procedures (translation services, cultural mediators) to increase the accessibility of interventions and improve adherence among immigrant families. In this brief review, we provide an overview about what is currently known about the epidemiology and risk factors of neurodevelopmental disorders, paying special attention to autism spectrum disorder (ASD), in children of immigrants and suggest the necessity of population-based screening and culturally sensitive care.

Brain Disorders and Chemical Pollutants: A Gap Junction Link?

The incidence of brain pathologies has increased during last decades. Better diagnosis (autism spectrum disorders) and longer life expectancy (Parkinson's disease, Alzheimer's disease) partly explain this increase, while emerging data suggest pollutant exposures as a possible but still underestimated cause of major brain disorders. Taking into account that the brain parenchyma is rich in gap junctions and that most pollutants inhibit their function; brain disorders might be the consequence of gap-junctional alterations due to long-term exposures to pollutants. In this article, this hypothesis is addressed through three complementary aspects: (1) the gap-junctional organization and connexin expression in brain parenchyma and their function; (2) the effect of major pollutants (pesticides, bisphenol A, phthalates, heavy metals, airborne particles, etc.) on gap-junctional and connexin functions; (3) a description of the major brain disorders categorized as neurodevelopmental (autism spectrum disorders, attention deficit hyperactivity disorders, epilepsy), neurobehavioral (migraines, major depressive disorders), neurodegenerative (Parkinson's and Alzheimer's diseases) and cancers (glioma), in which both connexin dysfunction and pollutant involvement have been described. Based on these different aspects, the possible involvement of pollutant-inhibited gap junctions in brain disorders is discussed for prenatal and postnatal exposures.

Neurotoxic effects of combined exposures to aluminum and mercury in early life (infancy)

Aluminum and mercury are environmentally ubiquitous. Individually they are both neurotoxic elements with shared neuro-pathogenic pathways: oxidative stress, altered neurotransmission, and disruption of the neuroendocrine and immune systems. In the infant, Al and Hg differ in type of exposure, absorption, distribution (brain access), and metabolism. In environmentally associated exposure (breast milk and infant formulas) their co-occurrences fluctuate randomly, but in Thimerosal-containing vaccines (TCVs) they occur combined in a proprietary ratio; in these cases, low-doses of Thimerosal-ethylmercury (EtHg) and adjuvant-Al present the most widespread binary mixture in less developed countries. Although experimental studies at low doses of the binary Hg and Al mixture are rare, when studied individually they have been shown to affect neurological outcomes negatively. In invitro systems, comparative neurotoxicity between Al and Hg varies in relation to the measured parameters but seems less for Al than for Hg. While neurotoxicity of environmental Hg (mainly fish methyl-Hg, MeHg) is associated with neurobehavioral outcomes in children, environmental Al is not associated, except in certain clinical conditions. Therefore, the issues of their neurotoxic effects (singly or combined) are discussed. In the infant (up to six months) the organic-Hg and Al body burdens from a full TCV schedule are estimated to reach levels higher than that originating from breastfeeding or from high aluminum soy-based formulas. Despite worldwide exposure to both Al and Hg (inorganic Hg, MeHg, and Thimerosal/EtHg), our knowledge on this combined exposure is insufficient to predict their combined neurotoxic effects (and with other co-occurring neurotoxicants).

A High Prevalence of Autism Spectrum Disorder in Preschool Children in an Immigrant, Multiethnic Population in Sweden: Challenges for Health Care

This study examines the prevalence of autism spectrum disorder (ASD) in preschool children in an immigrant population. Possible risk factors for ASD and individual needs for the children and their families are described, as well as implications for health care. The estimated minimum prevalence for ASD in the area was 3.66% for children aged 2–5 years. Multiple risk factors and extensive individual needs for the children and their families were observed. The high prevalence of ASD and the plethora of needs in immigrant communities pose challenges for health care. A coordinated health care system is necessary to meet the many and individual needs.

Genetic and Epigenetic Etiology Underlying Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a pervasive neurodevelopmental disorder characterized by difficulties in social interaction, language development delays, repeated body movements, and markedly deteriorated activities and interests. Environmental factors, such as viral infection, parental age, and zinc deficiency, can be plausible contributors to ASD susceptibility. As ASD is highly heritable, genetic risk factors involved in neurodevelopment, neural communication, and social interaction provide important clues in explaining the etiology of ASD. Accumulated evidence also shows an important role of epigenetic factors, such as DNA methylation, histone modification, and noncoding RNA, in ASD etiology. In this review, we compiled the research published to date and described the genetic and epigenetic epidemiology together with environmental risk factors underlying the etiology of the different phenotypes of ASD.

Maternal blood folate status during early pregnancy and occurrence of autism spectrum disorder in offspring: a study of 62 serum biomarkers

BACKGROUND

Autism spectrum disorder (ASD) evolves from an interplay between genetic and environmental factors during prenatal development. Since identifying maternal biomarkers associated with ASD risk in offspring during early pregnancy might result in new strategies for intervention, we investigated maternal metabolic biomarkers in relation to occurrence of ASD in offspring using both univariate logistic regression and multivariate network analysis.

METHODS

Serum samples from 100 women with an offspring diagnosed with ASD and 100 matched control women with typically developing offspring were collected at week 14 of pregnancy. Concentrations of 62 metabolic biomarkers were determined, including amino acids, vitamins (A, B, D, E, and K), and biomarkers related to folate (vitamin B₉) metabolism, lifestyle factors, as well as C-reactive protein (CRP), the kynurenine-tryptophan ratio (KTR), and neopterin as markers of inflammation and immune activation.

RESULTS

We found weak evidence for a positive association between higher maternal serum concentrations of folate and increased occurrence of ASD (OR per 1 SD increase: 1.70, 95% CI 1.22-2.37, FDR adjusted P = 0.07). Multivariate network analysis confirmed expected internal biochemical relations between the biomarkers. Neither inflammation markers nor vitamin D₃ levels, all hypothesized to be involved in ASD etiology, displayed associations with ASD occurrence in the offspring.

CONCLUSIONS

Our findings suggest that high maternal serum folate status during early pregnancy may be associated with the occurrence of ASD in offspring. No inference about physiological mechanisms behind this observation can be made at the present time because blood folate levels may have complex relations with nutritional intake, the cellular folate status and status of other B-vitamins. Therefore, further investigations, which may clarify the potential role and mechanisms of maternal blood folate status in ASD risk and the interplay with other potential risk factors, in larger materials are warranted.

Maternal exposure to air pollution and risk of autism in children: A systematic review and meta-analysis

BACKGROUND

The number of children diagnosed with autism spectrum disorder (ASD) has been increasing. Previous studies suggested potential association between pregnancy air pollution exposure and ASD. This systematic review and meta-analysis is intended to summarize the association between maternal exposure to outdoor air pollution and ASD in children by trimester based on recent studies.

METHODS

A systematic literature search in 3 databases (Medline, Embase, and Web of Science) was performed using subject headings related to ASD and air pollution since 2007. Eligible studies were screened and evaluated based on predetermined criteria. For meta-analyses, the studies were grouped by air pollutant and exposure time (prenatal period and trimesters). Within-group studies were standardized by log odds ratio (OR) and then combined by three meta-analysis methods: frequentist fixed and random effects models, and Bayesian random effects model.

RESULTS

Initial search identified 1564 papers, of which 25 studies remained for final analysis after duplicates and ineligible studies were removed. Of the 25 studies, 13, 14, 12, and 7 studies investigated ASD in children associated with PM_2.5, PM₁₀, NO₂, and ozone, respectively. The frequentist and Bayesian random effects models resulted in different statistical significance. For prenatal period, frequentist meta-analysis returned significant pooled ORs with 95% confidence intervals, 1.06(1.01,1.11) for PM_2.5 and 1.02(1.01,1.04) for NO₂, whereas Bayesian meta-analysis showed similar ORs with wider 95% posterior intervals, 1.06(1.00,1.13) for PM_2.5 and 1.02(1.00,1.05) for NO₂. Third trimester appeared to have higher pooled ORs for PM_2.5, PM₁₀, and ozone, but patterns in the time-varying associations over the trimester were inconsistent.

CONCLUSIONS

For positive association between maternal exposure to ambient air pollution and ASD in children, there is some evidence for PM_2.5, weak evidence for NO₂ and little evidence for PM₁₀ and ozone. However, patterns in associations over trimesters were inconsistent among studies and among air pollutants.

Chronic Fluoride Exposure and the Risk of Autism Spectrum Disorder

The continuous rise of autism spectrum disorder (ASD) prevalent in the past few decades is causing an increase in public health and socioeconomic concern. A consensus suggests the involvement of both genetic and environmental factors in the ASD etiopathogenesis. Fluoride (F) is rarely recognized among the environmental risk factors of ASD, since the neurotoxic effects of F are not generally accepted. Our review aims to provide evidence of F neurotoxicity. We assess the risk of chronic F exposure in the ASD etiopathology and investigate the role of metabolic and mitochondrial dysfunction, oxidative stress and inflammation, immunoexcitotoxicity, and decreased melatonin levels. These symptoms have been observed both after chronic F exposure as well as in ASD. Moreover, we show that F in synergistic interactions with aluminum's free metal cation (Al3+) can reinforce the pathological symptoms of ASD. This reinforcement takes place at concentrations several times lower than when acting alone. A high ASD prevalence has been reported from countries with water fluoridation as well as from endemic fluorosis areas. We suggest focusing the ASD prevention on the reduction of the F and Al3+ burdens from daily life.

Maternal immigrant status and signs of neurodevelopmental problems in early childhood: The French representative ELFE birth cohort

A growing body of evidence suggests that children of immigrants may have increased risks of neurodevelopmental disorders. However, evidence based on parent report and on very young children is lacking. We therefore investigated the association between maternal immigrant status and early signs of neurodevelopmental problems in a population-based sample of 2-year-old children using standardized parent-report instruments. We used data from the French representative Étude Longitudinale Française depuis l'Enfance birth cohort, initiated in 2011. The study sample included 9,900 children of nonimmigrant French, 1,403 children of second, and 1,171 children of first generation immigrant women followed-up to age 2 years. Neurodevelopment was assessed using the Modified Checklist for Autism in Toddlers (M-CHAT) and an adaptation of the MacArthur-Bates Communicative Development Inventories (MB-CDI). In fully adjusted linear regression models, maternal immigrant status was associated with M-CHAT scores, with stronger associations in children of first (β-coefficient: 0.19; 95% CI 0.08-0.29) than second generation immigrants (0.09; 0.01-0.17). This association was especially strong among children of first generation immigrant mothers native of North Africa (vs. nonimmigrant French: 0.33; 0.16-0.49) and French-speaking Sub-Saharan Africa (0.26; 0.07-0.45). MB-CDI scores were lowest among children of first generation immigrant mothers, particularly from mostly non-francophone regions. Children of first generation immigrant mothers were most likely to have simultaneously low MB-CDI and high M-CHAT scores. Our findings suggest that maternal immigrant status is associated with early signs of neurodevelopmental difficulties, with strong variations according to maternal region of origin. Further research is necessary to test whether these associations persist and to determine the underlying mechanisms. Autism Res 2019, 12: 1845-1859. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: We asked immigrant and nonimmigrant mothers in France about early signs of neurodevelopmental problems in their 2-year-old children. Overall, we found that children of immigrants may be at higher risk of showing these early warning signs, as compared to children of nonimmigrants. This is in line with previous studies, which were based on doctors' diagnoses at later ages. However, our results differed depending on the mothers' regions of origin. We found the highest risks in children of first generation immigrants from North and French-speaking Sub-Saharan Africa, who also seemed especially at risk of neurodevelopmental problems combined with low language development.

Autism spectrum disorder

Sources of data

This article is based on key recent published literature including international guidelines and relevant reviews and meta-analyses. Authors have also supplemented this material with their own clinical experience.

Areas of agreement

There is an agreement that autism spectrum disorder (ASD) have a strong hereditary component. There is also a consensus that the reported prevalence estimates have increased in the last 5 years. There is strong support for using the broader spectrum disorder conceptualization of the DSM-5.

Areas of controversy

Higher public awareness of ASD has generated several controversial theories of causation. We review a number of environmental risk factors receiving media attention including: vaccines, mercury, heavy metal exposure and Selective Serotonin Uptake Inhibitors (SSRIs). Popular yet controversial treatment interventions are discussed. Early diagnostic screening tools are also addressed.

Growing points

There is increasing scientific interest in identifying biomarkers of autism with potential for early diagnosis, prognostic indicators and predictive treatment responses. We review evidence from genetics, neuroimaging and eye tracking as candidate biomarkers.

Area timely for developing research

Family studies point to a strong hereditary component in the aetiology of autism. However these studies have not established 100% concordance rates, suggesting a role for environmental factors. The gene-environment interplay has not received enough attention in scientific research. This represents an important new avenue for research in ASD.

The use of iPSC technology for modeling Autism Spectrum Disorders

Autism Spectrum Disorders (ASDs) are a group of neurodevelopmental disorders that influence social skills, involving communication, interaction, and behavior, usually with repetitive and restrictive manners. Due to the variety of genes involved in ASDs and several possible environmental factors influence, there is still no answer to what really causes syndromic and non-syndromic types of ASDs, usually affecting each individual in a unique way. However, we know that the mechanism underlying ASDs involves brain functioning. The human brain is a complex structure composed of close to 100 billion cells, which is a big challenge to study counting just with post mortem tissue investigation or genetic approaches. Therefore, human induced pluripotent stem cells (iPSC) technology has been used as a tool to produce viable cells for understanding a working brain. Taking advantage of patient-derived stem cells, researchers are now able to generate neurons, glial cells and brain organoids in vitro to model ASDs. In this review we report data from different studies showing how iPSCs have been a critical tool to study the different phenotypes of ASDs.

Association Between Breastfeeding Initiation and Duration and Autism Spectrum Disorder in Preschool Children Enrolled in the Study to Explore Early Development

Studies report inconsistent findings on the relationship between ASD and breastfeeding. We explored associations between ASD and breastfeeding initiation (yes/no) and duration (months categorized in tertiles) in the Study to Explore Early Development, a community-based case-control study in six sites in the Unites States. We adjusted for various child and mother demographic and pregnancy factors. Breastfeeding initiation was reported in 85.7% of mothers of children with ASD and 90.6% of mothers of controls. After adjustment, we found no significant difference in breastfeeding initiation (adjusted odds-ratio [aOR]: 0.88 and 95% confidence interval (CI) 0.60-1.28). However, mothers of children with ASD were less likely to report duration of breastfeeding in the high (≥12 months) versus low tertile (<6 months) (aOR and 95% CI: 0.61 [0.45-0.84]) or the middle (6-<12 months) versus low tertile (0.72: 0.54-0.98). The association of ASD and breastfeeding duration was slightly attenuated when the presence of the broader autism phenotype (BAP) in the mother was accounted for, but still remained for the highest tertile. This association does not appear to be totally explained by maternal BAP. We were unable to distinguish whether the difference in duration was due to difficulties breastfeeding children who later develop ASD, other factors not adjusted in our study, or greater ASD risk resulting from shorter breastfeeding duration. Longitudinal studies that compare reasons why mothers stop breastfeeding between ASD and controls and establish a temporal relation between ASD and breastfeeding are needed. Future studies should also evaluate interactions between ASD risk genes and breastfeeding. Autism Research 2019, 12: 816-829. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: In this study, we compared breastfeeding practices between mothers of children with and without autism spectrum disorder (ASD). We found that the percentage of mothers who started breastfeeding was similar between the two groups, but mothers of children with ASD breastfed for a shorter amount of time compared to mothers of children without ASD. Future studies are needed to evaluate the reasons why the duration of breastfeeding was shorter for mothers of children with ASD compared to those without ASD.

Towards a fuller assessment of benefits to children's health of reducing air pollution and mitigating climate change due to fossil fuel combustion

BACKGROUND

Fossil fuel combustion by-products, including particulate matter (PM_2.5), polycyclic aromatic hydrocarbons (PAH), nitrogen dioxide (NO₂) and carbon dioxide (CO₂), are a significant threat to children's health and equality. Various policies to reduce emissions have been implemented to reduce air pollution and mitigate climate change, with sizeable estimated health and economic benefits. However, only a few adverse outcomes in children have been considered, resulting in an undercounting of the benefits to this vulnerable population.

OBJECTIVES

Our goal was to expand the suite of child health outcomes addressed by programs to assess health and economic benefits, such as the Environmental Protection Agency (EPA) Benefits Mapping and Analysis Program (BenMAP), by identifying concentration-response (C-R) functions for six outcomes related to PM_2.5, NO₂, PAH, and/or PM₁₀: preterm birth (PTB), low birthweight (LBW), autism, attention deficit hyperactivity disorder, IQ reduction, and the development of childhood asthma.

METHODS

We conducted a systematic review of the literature published between January 1, 2000 and April 30, 2018 to identify relevant peer-reviewed case-control and cohort studies and meta-analyses. In some cases meta-analyses were available that provided reliable C-R functions and we assessed their consistency with subsequent studies. Otherwise, we reviewed all eligible studies published between our search dates.

RESULTS

For each pollutant and health outcome, we present the characteristics of each selected study. We distinguish between C-R functions for endpoints having a causal or likely relationship (PTB, LBW, autism, asthma development) with the pollutants for incorporation into primary analyses and endpoints having a suggestive causal relationship with the pollutants (IQ reduction, ADHD) for secondary analyses.

CONCLUSION

We have identified C-R functions for a number of adverse health outcomes in children associated with air pollutants largely from fossil fuel combustion. Their incorporation into expanded assessments of health benefits of clean air and climate mitigation policies will provide an important incentive for preventive action.

Environmental Chemicals and Autism: A Scoping Review of the Human and Animal Research

BACKGROUND

Estimates of autism prevalence have increased dramatically over the past two decades. Evidence suggests environmental factors may contribute to the etiology of the disorder.

OBJECTIVES

This scoping review aimed to identify and categorize primary research and reviews on the association between prenatal and early postnatal exposure to environmental chemicals and the development of autism in epidemiological studies and rodent models of autism.

METHODS

PubMed was searched through 8 February 2018. Included studies assessed exposure to environmental chemicals prior to 2 months of age in humans or 14 d in rodents. Rodent studies were considered relevant if they included at least one measurement of reciprocal social communicative behavior or repetitive and stereotyped behavior. Study details are presented in interactive displays using Tableau Public.

RESULTS

The search returned 21,603 unique studies, of which 54 epidemiological studies, 46 experimental rodent studies, and 50 reviews were deemed relevant, covering 152 chemical exposures. The most frequently studied exposures in humans were particulate matter ([Formula: see text]), mercury ([Formula: see text]), nonspecific air pollution ([Formula: see text]), and lead ([Formula: see text]). In rodent studies, the most frequently studied exposures were chlorpyrifos ([Formula: see text]), mercury ([Formula: see text]), and lead ([Formula: see text]).

DISCUSSION

Although research is growing rapidly, wide variability exists in study design and conduct, exposures investigated, and outcomes assessed. Conclusions focus on recommendations to guide development of best practices in epidemiology and toxicology, including greater harmonization across these fields of research to more quickly and efficiently identify chemicals of concern. In particular, we recommend chlorpyrifos, lead, and polychlorinated biphenyls (PCBs) be systematically reviewed in order to assess their relationship with the development of autism. There is a pressing need to move forward quickly and efficiently to understand environmental influences on autism in order to answer current regulatory questions and inform treatment and prevention efforts. https://doi.org/10.1289/EHP4386.

Family Physicians' Awareness of Autism Spectrum Disorder: Results from a Survey Study

AIM:

Autism spectrum disorder (ASD) is a common neurodevelopmental disorder in children. Family physicians with the first medical contact of children are among the most frequent physicians with ASD. We aimed to investigate family physicians’ awareness of ASD.

METHODS:

This study was carried out family physicians in between September 25-October 15, 2018. The questionnaire form on autism awareness prepared by the researcher was delivered to family physicians electronically and in printed form, and it was filled out by volunteers.

RESULTS:

Forty-eight family physicians with an average professional experience of 16.9 ± 8.8 years participated in the study. A group of 66.7% of the participants had not previously received education on ASD, and 70.8% of them did not refer any child to child psychiatry with suspected ASD in the last 6 months. The participants stated that the most common clinical features in children with ASD were the inability to make eye contact (72.9%) and repetitive movements (47.9%), and 56.3% of them stated one or more features that are not observed in ASD. The compliance of the participants’ answers about the clinical features observed in children with ASD with the DSM-5 criteria was determined to be 54.6 ± 18.4%. Significantly higher compliance rates were observed in the participants with education on autism and those working as a physician below 15 years.

CONCLUSION:

In our study, family physicians’ awareness of ASD was not found to be adequate. Education programs on autism awareness should be applied to family physicians who are probably the most frequently encountered physicians by children with ASD.

Genetic association of DNMT variants can play a critical role in defining the methylation patterns in autism

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with impairments in social communication, restricted, repetitive and stereotyped behaviors. Both genetic and environmental factors are known to contribute toward pathophysiology of Autism. Environmental influences on gene expression can be mediated by methylation patterns which are established and maintained by DNA methyltransferases. Several studies in the past have investigated the role of global methylations in Autism. The present study is aimed to investigate the role of genetic variations in the DNA methyltransferase which might be critical in defining the threshold for environmental factors toward susceptibility to autism. Polymorphisms in DNA methyltransferases, DNMT1, DNMT3A, DNMT3B, and DNMT3L were screened for association with ASD in 180 autistic patients and 260 healthy controls from a south Indian population. DNMT1 rs10418707 and rs10423341, and DNMT3A rs2289195 were found to be significantly associated at genotypic and allelic level with ASD. Functional prediction indicates that these SNPs have a role in transcriptional regulation and increased expression, indicating that hypermethylation might be induced by its genotype status. The study might reflect the role of genetics variants in DNMTs in defining the threshold of environmental impact in influencing the disease or phenotype variations in ASD. © 2019 IUBMB Life, 2019.

The Relevance of Variants With Unknown Significance for Autism Spectrum Disorder Considering the Genotype-Phenotype Interrelationship

Several efforts in basic and clinical research have been contributing to unveiling the genetics behind autism spectrum disorders (ASD). However, despite these advancements, many individuals diagnosed with ASD and related neuropsychiatric conditions have been genetically investigated without elucidative results. The enormous genetic complexity of ASD-related conditions makes it a significant challenge to achieve, with a growing number of genes (close to a thousand) involved, belonging to different molecular pathways and presenting distinct genetic variations. Next-generation sequencing (NGS) is the approach most used in genetic research related to ASD, identifying de novo mutation, which is closely related to more severe clinical phenotypes, especially when they affect constrained and loss-of-function intolerant genes. On the other hand, de novo mutation findings contribute to a small percentage of the ASD population, since most of the cases and genetic variants associated with neuropsychiatric conditions are inherited and phenotypes are results of additive polygenic models, which makes statistical efforts more difficult. As a result, NGS investigation can sound vainly or unsuccessful, and new mutations on genes already related with ASD are classified as variants of unknown significance (VUS), hampering their endorsement to a clinical phenotype. This review is focused on currently available strategies to clarify the impact of VUS and to describe the efforts to identify more pieces of evidence throughout clinical interpretation and genetic curation process.

Glutamate, Glutamine and GABA Levels in Rat Brain Measured Using MRS, HPLC and NMR Methods in Study of Two Models of Autism

The disorders of the glutamatergic neurotransmission have been associated with pathogenesis of autism. In this study we evaluated the impact of the in vivo and ex vivo test methodology on measurements of levels of neurotransmitter amino acids in hippocampus of rats for valproic acid- (VPA) and thalidomide- (THAL) induced models of autism. The main goal was to compare the changes in concentrations of glutamate (Glu), glutamine (Gln) and GABA between both autistic groups and the control, measured in vivo and ex vivo in homogenates. The rat pups underwent three in vivo tests: ultrasonic vocalization (USV), magnetic resonance spectroscopy (MRS) and unilateral microdialysis of the hippocampus. Analyses of homogenates of rat hippocampus were performed using high-performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy. For the statistical analysis, we performed univariate and multivariate tests. USV test, which is considered in rodents as an indicator of pathology similar to autism, showed decreased USV in VPA and THAL groups. In vivo MRS studies demonstrated increases of Glu content in male rat's hippocampus in VPA and THAL groups, while the microdialysis, which allows examination of the contents in the extracellular space, detected decreases in the basal level of Gln concentrations in VPA and THAL groups. Ex vivo HPLC studies showed that levels of Glu, Gln and GABA significantly increased in male rat's hippocampus in the VPA and THAL groups, while NMR studies showed increased levels of Gln and GABA in the VPA group. Collectively, these results are consistent with the hypothesis suggesting the role of the glutamatergic disturbances on the pathogenesis of autism. For all methods used, the values of measured changes were in the same direction. The orthogonal partial least square discriminant analysis confirmed that both animal models of autism tested here can be used to trace neurochemical changes in the brain.

Multiple low-level exposures: Hg interactions with co-occurring neurotoxic substances in early life

All chemical forms of Hg can affect neurodevelopment; however, low levels of organic Hg (methylmercury-MeHg and ethylmercury-EtHg in Thimerosal-containing vaccines, hereafter 'TCV') exposures during early life (pregnancy and lactation) co-occur with other environmental neurotoxic substances. These neurotoxicants may act in parallel, synergistically, or antagonistically to Hg. Nevertheless, the risks of neurotoxicity associated with multiple neuro-toxicants depend on type, time, combinations of exposure, and environmental and/or genetic-associated factors. Neurological developmental disorders, delays in cognition and behavioral outcomes associated with multiple exposures (which include Hg) may show transient or lasting outcomes depending on constitutional and/or environmental factors that can interact to neutralize, aggravate or attenuate these effects; often these studies are challenging to interpret. During pregnancy and lactation, fish-MeHg exposure is frequently confounded with the opposing effects of neuroactive nutrients (in fish) that lead to positive, negative, or no effects on neurobehavioral tests. In infancy, exposures to acute binary mixtures (TCV- EtHg and Al-adjuvants in infant immunizations) are associated with increased risks of tics and other developmental disorders. Despite the certitude that promulgates single environmental neurotoxicants, empirical comparisons of combined exposures indicate that Hg-related outcome is uneven. Hg in combination with other neurotoxic mixtures may elevate risks of neurotoxicity, but these risks arise in circumstances that are not yet predictable. Therefore, to achieve the goals of the Minamata treaty and to safeguard the health of children, low levels of mercury exposure (in any chemical form) needs to be further reduced whether the source is environmental (air- and food-borne) or iatrogenic (pediatric TCVs).

Evaluation of antibodies to cytomegalovirus and Epstein-Barr virus in patients with autism spectrum disorder

Autism is a neurodevelopmental disease that manifested by a wide range of behavioral disorders. Although the etiology of autism is remained unknown but it is suggested that ASD have a complex etiology, including genetic and environmental factors, which may explain the observed different behavioral disorders in these patients. One of the proposed reasons for autism is viral infection in the early stages of development. The mechanism by which viral infection could lead to autism is still unclear.Previous studiesemphasized on the role of family membersof Herpesviruses in autism susceptibility. In this study, anti-Cytomegalovirus (CMV) and anti-Epstein-Barr virus (EBV) antibodies in the serum of 45 children with autism and 45 healthy individuals were evaluated. Serum samples were isolated from 5 ml blood of the patients and controls. Sandwich ELISA was used to quantitatively measure antibodies against the mentioned viruses. Results analyzed by SPSS software showed an increased amount of anti-CMV IgG and IgM antibodies in the blood of patients with Autism but not statistically significant (P< 0.05). The anti-EBV IgM antibody in the blood of patients with Autism was not only increased but also statistically significant (P< 0.05), however, the IgG level against EBV in the serum of ASD patients showed no significant difference in comparison to healthy controls. So it can be said that although the mechanisms of viral infection in autism is unknown, but probably EBV infection is associated with an increased risk of autism.

Prevalence of Autism Spectrum Disorder in Preterm Infants: A Meta-analysis

CONTEXT

Evidence is emerging that preterm infants are at risk for autism spectrum disorder (ASD).

OBJECTIVES

To conduct a systematic review and meta-analysis to estimate the prevalence of ASD in preterm infants.

DATA SOURCES

Medline (via PubMed and Ovid), Embase, PsycINFO, and relevant conference proceedings were searched in May 2017.

STUDY SELECTION

Original studies in which researchers report on the prevalence of ASD using diagnostic tests in children born preterm were included. Studies in which researchers used only ASD screening tools were excluded.

DATA EXTRACTION

Relevant data were extracted independently by 3 authors.

RESULTS

Researchers in a total of 18 studies (3366 preterm infants) used ASD diagnostic tools. The median gestation, birth weight, and age at assessment were 28.0 weeks (range: 25.1-31.3 weeks), 1055 g (range: 719-1565 g), and 5.7 years (range: 1.5-21 years), respectively. Meta-analysis revealed that the overall prevalence rate for ASD was 7% (95% confidence interval: 4% to 9%). The funnel plot and Egger's test revealed that there was probably no evidence of publication bias.

LIMITATIONS

The limitations were significant heterogeneity and a lack of studies from middle- and low-income countries.

CONCLUSIONS

The prevalence of ASD is significantly high in the preterm population. Adequate resources are needed to improve the outcomes of these children.

Parents' and guardians' experiences of barriers and facilitators in accessing autism spectrum disorder diagnostic services for their children: a systematic review protocol of qualitative evidence

REVIEW QUESTION

What are parents' and guardians' experiences of barriers and facilitators in accessing autism spectrum disorder diagnostic services for their children?