On the Complex Relationship Between Genes and Environment in the Etiology of Autism

Machine Learning Assisted Discovery of Interactions between Pesticides, Phthalates, Phenols, and Trace Elements in Child Neurodevelopment

A growing body of literature suggests that developmental exposure to individual or mixtures of environmental chemicals (ECs) is associated with autism spectrum disorder (ASD). However, investigating the effect of interactions among these ECs can be challenging. We introduced a combination of the classical exposure-mixture Weighted Quantile Sum (WQS) regression and a machine-learning method termed Signed iterative Random Forest (SiRF) to discover synergistic interactions between ECs that are (1) associated with higher odds of ASD diagnosis, (2) mimic toxicological interactions, and (3) are present only in a subset of the sample whose chemical concentrations are higher than certain thresholds. In a case-control Childhood Autism Risks from Genetics and Environment (CHARGE) study, we evaluated multiordered synergistic interactions among 62 ECs measured in the urine samples of 479 children in association with increased odds for ASD diagnosis (yes vs no). WQS-SiRF identified two synergistic two-ordered interactions between (1) trace-element cadmium (Cd) and the organophosphate pesticide metabolite diethyl-phosphate (DEP); and (2) 2,4,6-trichlorophenol (TCP-246) and DEP. Both interactions were suggestively associated with increased odds of ASD diagnosis in the subset of children with urinary concentrations of Cd, DEP, and TCP-246 above the 75th percentile. This study demonstrates a novel method that combines the inferential power of WQS and the predictive accuracy of machine-learning algorithms to discover potentially biologically relevant chemical-chemical interactions associated with ASD.

Hypertensive disorders of pregnancy and occurrence of ADHD, ASD, and epilepsy in the child: A meta-analysis

AIM

To synthesize epidemiologic literature pertaining to the association between preeclampsia (PE), attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and epilepsy.

METHOD

A systematic search of PubMed and Embase was performed supplemented by hand-searching of reference lists of eligible studies. Two independent reviewers screened abstracts following a prepared protocol. Data extraction and quality appraisal using the Newcastle Ottawa Scale were performed by an independent reviewer. PRISMA guidelines were followed throughout. Random-effects meta-analyses were performed. Adjusted pooled Odds Ratios and their 95% confidence intervals were reported.

RESULTS

Fifteen out of 121 identified studies were eligible for inclusion. Six reported adjusted estimates for ADHD, resulting in a pooled odds ratio of 1.29 (95% CI: 1.20, 1.38). Eight reported adjusted estimates for ASD, resulting in a pooled odds ratio of 1.27 (95% CI:1.22, 1.32). Three reported adjusted estimates for epilepsy, resulting in a pooled odds ratio of 1.35 (95% CI: 1.12, 1.63).

INTERPRETATION

Intrauterine exposure to PE increased the risk of ADHD, ASD, and epilepsy, though it is unclear whether the true association is with pre-term birth. To our knowledge, this is the first meta-analysis to quantify the association between PE and epilepsy. The results of this meta-analysis can inform screening strategies among children born to preeclamptic mothers for early identification and treatment.

Pre-eclampsia and the risk of autism-spectrum disorder in offspring: meta-analysis

BACKGROUND

Evidence about the effect of intrauterine exposure to pre-eclampsia on offspring autism-spectrum disorder (ASD) is not well established. Aims To examine the association between pre-eclampsia and ASD.

METHOD

PubMed, Embase and PsycINFO databases were searched. Pooled relative risks (RR) with 95% confidence intervals were calculated. Subgroup and sensitivity analyses were performed. Heterogeneity was assessed using Cochran's Q- and the I 2-test. The presence of publication bias was evaluated by Egger's test and visual inspection of the symmetry in funnel plots.

RESULTS

Ten studies meet the inclusion criteria. The risk of ASD was 32% higher in offspring who had intrauterine exposure to pre-eclampsia compared with those not exposed (RR = 1.32, 95% CI 1.20-1.45). Sensitivity analysis revealed consistent pooled estimates ranging from RR = 1.30 (95% CI 1.17-1.44) to RR = 1.37 (95% CI 1.26-1.48). We found no significant heterogeneity and evidence of publication bias.

CONCLUSION

Pre-eclampsia increased the risk of ASD in offspring. The finding suggests a need for early screening for ASD in offspring of women with pre-eclampsia. Declaration of interest None.

Prevalence of Congenital Cytomegalovirus Infection Assessed Through Viral Genome Detection in Dried Blood Spots in Children with Autism Spectrum Disorders

BACKGROUND/AIM

Autism spectrum disorders (ASD) are neurodevelopmental disorders without a definitive etiology in most cases. Environmental factors, such as viral infections, have been linked with anomalies in brain growth, neuronal development, and functional connectivity. Congenital cytomegalovirus (CMV) infection has been associated with the onset of ASD in several case reports. The aim of this study was to evaluate the prevalence of congenital CMV infection in children with ASD and in healthy controls.

PATIENTS AND METHODS

The CMV genome was tested by polymerase chain reaction (PCR) on dried blood spots collected at birth from 82 children (38 with ASD and 44 controls).

RESULTS

The prevalence of congenital CMV infection was 5.3% (2/38) in cases and 0% (0/44) in controls (p=0.212).

CONCLUSION

The infection rate was about 10-fold higher in patients with ASD than in the general Italian population at birth. For this reason, detection of CMV-DNA on dried blood spots could be considered in the work-up that is usually performed at ASD diagnosis to rule-out a secondary form. Given the potential prevention and treatment of CMV infection, this study could have intriguing consequences, at least for a group of patients with ASD.

No evidence of congenital varicella zoster virus infection assessed through dried blood spot in children with autism spectrum disorders

Aim: Several authors have hypothesized an association between congenital viral infections and the onset of autism spectrum disorders (ASD). We aimed to assess the prevalence of congenital varicella zoster virus (VZV) infection in patients with ASD. Patients & methods: Congenital infection by VZV was evaluated in a cohort of 38 children with ASD and in 44 healthy controls. PCR for VZV-DNA performed on dried blood spots collected at birth. Results & conclusion: No VZV infection was detected in both groups. With the limitation of the small sample size of this study, the results are not in favor of a role of VZV in the etiology of ASD.

The maternal body as environment in autism science

Research on autism and environmental risk factors has expanded substantially in recent years. My analysis draws attention to the regimes of perceptibility that shape how the environment is materialized in post-genomic science. I focus on how more complex narratives of autism's causes and social anxieties surrounding child development have helped situate autism risk in women's bodies before and during pregnancy. This has resulted in what I call the maternal body as environment in autism science. I show that this figure involves three characteristics: the molecularization of the environment, an individualization of risk, and the internalization of responsibility. I argue that these three features point to a new spatial and temporal politics of risk and responsibility that may heighten social and medical surveillance of women's bodies and decisions, eclipsing larger questions about the uneven distribution of exposures in society and more holistic understandings of health that include neurodiversity. I conclude by considering what the maternal body as environment signals for women, social justice, and the politics of environmental health in the post-genomic era.

Comprehensive molecular testing in patients with high functioning autism spectrum disorder

Autism spectrum disorders (ASD) include a range of complex neurodevelopmental disorders with extreme genetic heterogeneity. Exome and target sequencing studies have shown to be an effective tool for the discovery of new ASD genes. The aim of this study was to design an ASD candidate gene panel that covers 44 of the top ASD candidate genes. As a pilot study we performed comprehensive molecular diagnostic testing, including the study of the FMR1 and FMR2 repeat regions, copy number variant analysis in a collection of 50 Spanish ASD cases and mutation screening using targeted next generation sequencing-based techniques in 44 out of the total cohort. We evaluated and clinically selected our cohort, with most of the cases having high functioning ASD without facial dysmorphic features. The results of the present study allowed the detection of copy number and single nucleotide variants not yet identified. In addition, our results underscore the difficulty of the molecular diagnosis of ASD and confirm its genetic heterogeneity. The information gained from this and other genetic screenings is necessary to unravel the clinical interpretation of novel variants.

Autism Spectrum Disorder - A Complex Genetic Disorder

Autism spectrum disorder is an entity that reflects a scientific consensus that several previously separated disorders are actually a single spectrum disorder with different levels of symptom severity in two core domains - deficits in social communication and interaction, and restricted repetitive behaviors. Autism spectrum disorder is diagnosed in all racial, ethnic and socioeconomic groups and because of its increased prevalence, reported worldwide through the last years, made it one of the most discussed child psychiatric disorders. In term of aetiology as several other complex diseases, Autism spectrum disorder is considered to have a strong genetic component.

Perinatal and background risk factors for childhood autism in central China

Perinatal and background risk factors for autism were identified in a cohort of autistic children in Zhengzhou, China, to formulate preventative and treatment strategies for high-risk families. In this case-control study, children were screened for suspected autism using the Autism Behavior Checklist (ABC) and diagnosed according to DSM-IV and the Childhood Autism Rating Scale (CARS). We collected perinatal histories and clinical data of 286 confirmed autistic children treated at the Third Affiliated Hospital Children׳s Psychological Clinic of Zhengzhou University from 2011 to 2013. The control group consisted of 286 healthy children from area kindergartens. Maternal age>30 years, parental introversion as measured by the Eysenck Personality Questionnaire, low level of parental education, smoking, abortion threat, pregnancy complications, maternal illness during pregnancy, maternal mental health, family history of mental illness, neonatal jaundice, birth asphyxia, premature rupture of the fetal membrane, and gestational age<37 weeks were significantly higher in the autism group. These factors were significantly correlated with behavioral symptoms as measured by ABC scores (Kendall rank correlation). Birth asphyxia, neonatal jaundice, maternal age, parental introversion, family history of mental illness, abortion threat, premature delivery, and smoking were identified as independent risk factors by multivariate logistic regression.

Environmental chemical exposures and autism spectrum disorders: a review of the epidemiological evidence

In the past decade, the number of epidemiological publications addressing environmental chemical exposures and autism has grown tremendously. These studies are important because it is now understood that environmental factors play a larger role in causing autism than previously thought and because they address modifiable risk factors that may open up avenues for the primary prevention of the disability associated with autism. In this review, we covered studies of autism and estimates of exposure to tobacco, air pollutants, volatile organic compounds and solvents, metals (from air, occupation, diet, dental amalgams, and thimerosal-containing vaccines), pesticides, and organic endocrine-disrupting compounds such as flame retardants, non-stick chemicals, phthalates, and bisphenol A. We included studies that had individual-level data on autism, exposure measures pertaining to pregnancy or the 1st year of life, valid comparison groups, control for confounders, and adequate sample sizes. Despite the inherent error in the measurement of many of these environmental exposures, which is likely to attenuate observed associations, some environmental exposures showed associations with autism, especially traffic-related air pollutants, some metals, and several pesticides, with suggestive trends for some volatile organic compounds (e.g., methylene chloride, trichloroethylene, and styrene) and phthalates. Whether any of these play a causal role requires further study. Given the limited scope of these publications, other environmental chemicals cannot be ruled out, but have not yet been adequately studied. Future research that addresses these and additional environmental chemicals, including their most common routes of exposures, with accurate exposure measurement pertaining to several developmental windows, is essential to guide efforts for the prevention of the neurodevelopmental damage that manifests in autism symptoms.

Screening of 50 cypriot patients with autism spectrum disorders or autistic features using 400K custom array-CGH

Autism spectrum disorders (ASDs) comprise a distinct entity of neurodevelopmental disorders with a strong genetic component. Despite the identification of several candidate genes and causative genomic copy number variations (CNVs), the majority of ASD cases still remain unresolved. We have applied microarray-based comparative genomic hybridization (array-CGH) using Agilent 400K custom array in the first Cyprus population screening for identification of ASD-associated CNVs. A cohort of 50 ASD patients (G1), their parents (G2), 50 ethnically matched normal controls (G3), and 80 normal individuals having children with various developmental and neurological conditions (G4) were tested. As a result, 14 patients were found to carry 20 potentially causative aberrations, two of which were de novo. Comparison of the four population groups revealed an increased rate of rare disease-associated variants in normal parents of children with autism. The above data provided additional evidence, supporting the complexity of ASD aetiology in comparison to other developmental disorders involving cognitive impairment. Furthermore, we have demonstrated the rationale of a more targeted approach combining accurate clinical description with high-resolution population-oriented genomic screening for defining the role of CNVs in autism and identifying meaningful associations on the molecular level.

Etiopathogenesis of autism spectrum disorders: fitting the pieces of the puzzle together

Autism spectrum disorders (ASD) are disorders of the central nervous system characterized by impairments in communication and social reciprocity. Despite thousands of studies on this topic, the etiopathogenesis of these disorders remains unclear, apart from a general belief that they derive from an interaction between several genes and the environment. Given the mystery surrounding the etiopathogenesis of ASD it is impossible to plan effective preventive and treatment measures. This is of particular concern due to the progressive increase in the prevalence of ASD, which has reached a figure as high as 1:88 children in the USA. Here we present data corroborating a novel unifying hypothesis of the etiopathogenesis of ASD. We suggest that ASD are disorders of the immune system that occur in a very early phase of embryonic development. In a background of genetic predisposition and environmental predisposition (probably vitamin D deficiency), an infection (notably a viral infection) could trigger a deranged immune response which, in turn, results in damage to specific areas of the central nervous system. If proven, this hypothesis would have dramatic consequences for strategies aimed at preventing and treating ASD. To confirm or refute this hypothesis, we need a novel research approach, which unlike former approaches in this field, examine the major factors implicated in ASD (genetic, infections, vitamin D deficiency, immune system deregulation) not separately, but collectively and simultaneously.