Explaining the Increase in the Prevalence of Autism Spectrum Disorders
A new study, by the Aarhus University, Department of Public Health, finds that most – 60% – of the autism rise over the last three decades in Denmark cases is due to changes in reporting practices. But still, changes in reporting practices fail to explain 40 percent of the rise, the researcher noted.
The prevalence of autism spectrum disorders (ASDs) has increased markedly in recent decades, which researchers have suggested could be caused in part by nonetiologic factors such as changes in diagnosis reporting practices. To our knowledge, no study has quantified the degree to which changes in reporting practices might explain this increase. Danish national health registries have undergone a change in diagnostic criteria in 1994 and the inclusion of outpatient contacts to health registries in 1995.
To quantify the effect of changes in reporting practices in Denmark on reported ASD prevalence.
Design, Setting, and Participants
We used a population-based birth cohort approach that includes information on all individuals with permanent residence in Denmark. We assessed all children born alive from January 1, 1980, through December 31, 1991, in Denmark (n = 677 915). The children were followed up from birth until ASD diagnosis, death, emigration, or the end of follow-up on December 31, 2011, whichever occurred first. The analysis uses a stratified Cox proportional hazards regression model with the changes in reporting practices modeled as time-dependent covariates.
The change in diagnostic criteria in 1994 and the inclusion of outpatient diagnoses in 1995.
Main Outcomes and Measures
Autism spectrum disorders.
For Danish children born during the study period, 33% (95% CI, 0%-70%) of the increase in reported ASD prevalence could be explained by the change in diagnostic criteria alone; 42% (95% CI, 14%-69%), by the inclusion of outpatient contacts alone; and 60% (95% CI, 33%-87%), by the change in diagnostic criteria and the inclusion of outpatient contacts.
Conclusions and Relevance
Changes in reporting practices can account for most (60%) of the increase in the observed prevalence of ASDs in children born from 1980 through 1991 in Denmark. Hence, the study supports the argument that the apparent increase in ASDs in recent years is in large part attributable to changes in reporting practices.
Sources and more information:
Altered diagnosis has led to growth in autism, Aarhus University News, 2014.11.04.
Explaining the Increase in the Prevalence of Autism Spectrum Disorders, JAMA Pediatr. Published online November 03, 2014. doi:10.1001/jamapediatrics.2014.1893.
Autism’s Rise: Researchers Look at Why Cases Are Increasing, livescience, November 03, 2014.
Beyond Vaccines: 5 Things that Might Really Cause Autism, livescience, January 07, 2011.
We are very excited to share ASD Project Brave in celebration of Autism Awareness Month in Canada
Children and adults with autism spectrum disorder face challenges with communication, social interaction, anxiety, sensory processing, the simple uncertainties of daily living, bullying, rejection and lack of supports for their needs.
They also laugh, dance, learn, give, share, teach, feel and love.
They are brave.
We challenge you to:
Make our world a place where their gifts, talents and unique qualities are appreciated and accepted.
Encourage governments, healthcare providers and school boards to find better ways to support them.
Disruptive CHD8 Mutations Define a Subtype of Autism Early in Development
In a collaboration involving 13 institutions around the world, researchers have broken new ground in understanding what causes autism. This is the first time researchers have shown a definitive cause of autism to a genetic mutation. Previously identified genetic events like Fragile X, which account for a greater number of autism cases, are associated with other impairments, such as intellectual disability, more than autism.
Autism spectrum disorder (ASD) is a heterogeneous disease in which efforts to define subtypes behaviorally have met with limited success. Hypothesizing that genetically based subtype identification may prove more productive, we resequenced the ASD-associated gene CHD8 in 3,730 children with developmental delay or ASD. We identified a total of 15 independent mutations; no truncating events were identified in 8,792 controls, including 2,289 unaffected siblings. In addition to a high likelihood of an ASD diagnosis among patients bearing CHD8 mutations, characteristics enriched in this group included macrocephaly, distinct faces, and gastrointestinal complaints. chd8 disruption in zebrafish recapitulates features of the human phenotype, including increased head size as a result of expansion of the forebrain/midbrain and impairment of gastrointestinal motility due to a reduction in postmitotic enteric neurons. Our findings indicate that CHD8 disruptions define a distinct ASD subtype and reveal unexpected comorbidities between brain development and enteric innervation.
Disruptive CHD8 Mutations Define a Subtype of Autism Early in Development, ScienceDirect, DOI: 10.1016/j.cell.2014.06.017 pii/S0092867414007491, 3 July 2014
Genetic link to autism found, known as CHD8 mutation, ScienceDaily, 140703125851, July 3, 2014
A number of ASD cases might be prevented by reducing SSRI exposure in pregnancy…
A new study from researchers at Drexel University adds evidence that using common antidepressant medications during pregnancy may contribute to a higher risk of autism spectrum disorders (ASD) in children, although this risk is still very small.
A number of ASD cases might be prevented by reducing SSRI exposure in pregnancy…
2014 Study Abstract
We investigated whether there is an association between increased risk for autism spectrum disorders (ASD) and selective serotonin reuptake inhibitors (SSRIs) used during pregnancy. This study used Denmark’s health and population registers to obtain information regarding prescription drugs, ASD diagnosis, and health and socioeconomic status. There were 1.5 % of cases and 0.7 % of controls exposed to SSRIs during the pregnancy period, and higher effect estimates observed with longer use. We found evidence that in utero exposure to SSRIs increases a child’s risk associated with ASD. These results, while adding to the limited knowledge on prenatal pharmacological exposures as potential ASD risk factors, need to be balanced against the benefits of indicated medication use by pregnant mothers.
In Utero Exposure to Antidepressants May Influence Autism Risk, DrexelNow, news-media, June 2, 2014
Epilepsy in young adults with autism: a prospective population-based follow-up study of 120 individuals diagnosed in childhood
Little is known about the long-term outcome of epilepsy in autism and the epilepsy characteristics of adults with autism. This prospective population-based study was conducted in an attempt to point out differences on a group basis between adults with autism with or without epilepsy, and to describe the occurrence, the seizure characteristics, and the outcome of epilepsy in autism.
One hundred eight of 120 individuals with autism diagnosed in childhood and followed up prospectively for a period of 13-22 years were reevaluated at ages 17-40 years. As adults, the majority had mental retardation and autistic disorder or autistic-like condition. Interviews were performed with the caretakers of 42 of 43 individuals with a history of epilepsy, and their medical records were reviewed.
Adults with autism and mental retardation constituted a severely disabled group. On a group basis, both the cognitive level and the adaptive behavior level were lower in the epilepsy group than in the nonepilepsy group (p<0.05). In all, 38% had epilepsy. One third had epilepsy onset before age 2 years. Remission of epilepsy was seen in 16%. Partial seizures with or without secondarily generalized seizures were the dominating seizure type.
In a community sample of individuals with autism followed up from childhood through to adult age, one of three had epilepsy since childhood/adolescence. Severe mental retardation and autism are significantly associated with epilepsy, especially in female patients. Seizure frequency has a great impact on the individuals’ lives. Specialist medical care is needed in this severely communication-disabled population.
Pathophysiology of Epilepsy in Autism Spectrum Disorders
Epilepsy occurs frequently in individuals with autism spectrum disorders (ASD). However, the mechanisms responsible for increased seizure susceptibility in ASD are largely unknown. Clues to neural hyperexcitability in the autistic brain might be derived from disorders in which single gene mutations cause both epilepsy and an autistic phenotype, such as fragile X syndrome and tuberous sclerosis complex. This chapter summarizes current understanding of epilepsy in individuals with ASD and explores potential links between the genetic disruption of neural circuits and cellular signaling pathways that contribute to both epilepsy and ASD.
Growing evidence that ASD is linked to pollution, with babies 283% more likely to suffer from the condition compared to other birth defects…
Environmental and State-Level Regulatory Factors Affect the Incidence of Autism and Intellectual Disability
A PLOS Computational Biology Journal article offers strong evidence that environmental toxins play a role in the autism spectrum disorder. The research looked at birth defects associated with parental exposure to pollution and found a 1% increase in the defects corresponded to a 283% increase in autism.
Many factors affect the risks for neurodevelopmental maladies such as autism spectrum disorders (ASD) and intellectual disability (ID). To compare environmental, phenotypic, socioeconomic and state-policy factors in a unified geospatial framework, we analyzed the spatial incidence patterns of ASD and ID using an insurance claims dataset covering nearly one third of the US population. Following epidemiologic evidence, we used the rate of congenital malformations of the reproductive system as a surrogate for environmental exposure of parents to unmeasured developmental risk factors, including toxins. Adjusted for gender, ethnic, socioeconomic, and geopolitical factors, the ASD incidence rates were strongly linked to population-normalized rates of congenital malformations of the reproductive system in males (an increase in ASD incidence by 283% for every percent increase in incidence of malformations, 95% CI: [91%, 576%], p<6×10−5). Such congenital malformations were barely significant for ID (94% increase, 95% CI: [1%, 250%], p = 0.0384). Other congenital malformations in males (excluding those affecting the reproductive system) appeared to significantly affect both phenotypes: 31.8% ASD rate increase (CI: [12%, 52%], p<6×10−5), and 43% ID rate increase (CI: [23%, 67%], p<6×10−5). Furthermore, the state-mandated rigor of diagnosis of ASD by a pediatrician or clinician for consideration in the special education system was predictive of a considerable decrease in ASD and ID incidence rates (98.6%, CI: [28%, 99.99%], p = 0.02475 and 99% CI: [68%, 99.99%], p = 0.00637 respectively). Thus, the observed spatial variability of both ID and ASD rates is associated with environmental and state-level regulatory factors; the magnitude of influence of compound environmental predictors was approximately three times greater than that of state-level incentives. The estimated county-level random effects exhibited marked spatial clustering, strongly indicating existence of as yet unidentified localized factors driving apparent disease incidence. Finally, we found that the rates of ASD and ID at the county level were weakly but significantly correlated (Pearson product-moment correlation 0.0589, p = 0.00101), while for females the correlation was much stronger (0.197, p<2.26×10−16).
Sources and Press releases
Environmental and State-Level Regulatory Factors Affect the Incidence of Autism and Intellectual Disability, PLOS Computational Biology, DOI: 10.1371/journal.pcbi.1003518, 13 March 2014
Air Pollution and Newly Diagnostic Autism Spectrum Disorders: A Population-Based Cohort Study in Taiwan
There is limited evidence that long-term exposure to ambient air pollution increases the risk of childhood autism spectrum disorder (ASD). The objective of the study was to investigate the associations between long-term exposure to air pollution and newly diagnostic ASD in Taiwan. We conducted a population-based cohort of 49,073 children age less than 3 years in 2000 that were retrieved from Taiwan National Insurance Research Database and followed up from 2000 through 2010. Inverse distance weighting method was used to form exposure parameter for ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and particles with aerodynamic diameter less than 10 µm (PM10). Time-dependent Cox proportional hazards (PH) model was performed to evaluate the relationship between yearly average exposure air pollutants of preceding years and newly diagnostic ASD. The risk of newly diagnostic ASD increased according to increasing O3, CO, NO2, and SO2 levels. The effect estimate indicating an approximately 59% risk increase per 10 ppb increase in O3 level (95% CI 1.42–1.79), 37% risk increase per 10 ppb in CO (95% CI 1.31–1.44), 340% risk increase per 10 ppb increase in NO2 level (95% CI 3.31–5.85), and 17% risk increase per 1 ppb in SO2 level (95% CI 1.09–1.27) was stable with different combinations of air pollutants in the multi-pollutant models. Our results provide evident that children exposure to O3, CO, NO2, and SO2 in the preceding 1 year to 4 years may increase the risk of ASD diagnosis.
Sources PLOSone September 25, 2013DOI: 10.1371/journal.pone.0075510
Autism Spectrum Disorders in Relation to Distribution of Hazardous Air Pollutants in the San Francisco Bay Area
To explore possible associations between autism spectrum disorders (ASD) and environmental exposures, we linked the California autism surveillance system to estimated hazardous air pollutant (HAP) concentrations compiled by the U.S. Environmental Protection Agency.
Subjects included 284 children with ASD and 657 controls, born in 1994 in the San Francisco Bay area. We assigned exposure level by census tract of birth residence for 19 chemicals we identified as potential neurotoxicants, developmental toxicants, and/or endocrine disruptors from the 1996 HAPs database. Because concentrations of many of these were highly correlated, we combined the chemicals into mechanistic and structural groups, calculating summary index scores. We calculated ASD risk in the upper quartiles of these group scores or individual chemical concentrations compared with below the median, adjusting for demographic factors.
The adjusted odds ratios (AORs) were elevated by 50% in the top quartile of chlorinated solvents and heavy metals [95% confidence intervals (CIs), 1.1–2.1], but not for aromatic solvents. Adjusting for these three groups simultaneously led to decreased risks for the solvents and increased risk for metals (AORs for metals: fourth quartile = 1.7; 95% CI, 1.0–3.0; third quartile = 1.95; 95% CI, 1.2–3.1). The individual compounds that contributed most to these associations included mercury, cadmium, nickel, trichloroethylene, and vinyl chloride.
Our results suggest a potential association between autism and estimated metal concentrations, and possibly solvents, in ambient air around the birth residence, requiring confirmation and more refined exposure assessment in future studies.
Sources NCBI Environ Health Perspect. Sep 2006; 114(9): 1438–1444 PMC1570060
To examine whether induced (stimulating uterine contractions prior to the onset of spontaneous labor) and/or augmented (increasing the strength, duration, or frequency of uterine contractions with spontaneous onset of labor) births are associated with increased odds of autism.
Design, Setting, and Participants
We performed an epidemiological analysis using multivariable logistic regression modeling involving the North Carolina Detailed Birth Record and Education Research databases. The study featured 625 042 live births linked with school records, including more than 5500 children with a documented exceptionality designation for autism.
Induced or augmented births.
Main Outcomes and Measures
Autism as assessed by exceptionality designations in child educational records.
Compared with children born to mothers who received neither labor induction nor augmentation, children born to mothers who were induced and augmented, induced only, or augmented only experienced increased odds of autism after controlling for potential confounders related to socioeconomic status, maternal health, pregnancy-related events and conditions, and birth year. The observed associations between labor induction/augmentation were particularly pronounced in male children.
Conclusions and Relevance
Our work suggests that induction/augmentation during childbirth is associated with increased odds of autism diagnosis in childhood. While these results are interesting, further investigation is needed to differentiate among potential explanations of the association including underlying pregnancy conditions requiring the eventual need to induce/augment, the events of labor and delivery associated with induction/augmentation, and the specific treatments and dosing used to induce/augment labor (eg, exogenous oxytocin and prostaglandins).
Association of Autism With Induced or Augmented Childbirth in North Carolina Birth Record (1990-1998) and Education Research (1997-2007) Databases