Does environmental exposure to the greenhouse gas, N2O, contribute to etiological factors in neurodevelopmental disorders? A mini-review of the evidence

Investigating global surface temperature from the perspectives of environmental, demographic, and economic indicators: current status and future temperature trend

Anthropogenic activities have increased atmospheric concentrations of greenhouse gas emissions, which have observably increased global temperature. Recognizing it as one of the most critical issues caused by human activities, this study investigates the effects of environmental, demographic, and economic indicators on global and regional temperature. For this purpose, advanced and powerful machine learning techniques, such as ANN, CNN, SVM, and LSTM, are employed using the data from 1980 to 2018 of the aforementioned regions to predict and forecast global and regional temperatures in Africa, Asia, Europe, North America, and South America. First, the predicted results were found very close to the actual surface temperature, confirming that environmental, economic, and demographic indicators are critical drivers of climate change. Second, this study forecasted global temperature from 2023 to 2050 and regional temperature from 2022 to 2050. The results also predicted a considerable increase in global temperature and regional temperature in the forthcoming years. Particularly, Asia and Africa may experience extreme weather in the future with an increase of more than 1.6 °C. Based on the findings of this study, the major implications have been that maintaining greenhouse gas emissions, balancing economic development, urbanization, and environmental quality while reducing fossil fuel energy consumption will ensure climate mitigation. The findings demand an alteration in human behavior regarding fossil fuel energy consumption to control greenhouse gas emissions, which is the most significant contributor to climate change.

Parental Occupational Exposure and Neurodevelopmental Disorders in Offspring: a Systematic Review and Meta-analysis

PURPOSE OF REVIEW

Parental occupational exposures might be associated with neurodevelopmental disorders (NDDs) in offspring. We aimed to conduct a systematic review and meta-analysis to summarize and synthesize the current literature and to estimate the pooled magnitude of the underlying association(s) between parental occupational exposures and subsequent risk of NDDs.

RECENT FINDINGS

In the meta-analysis of 20 included studies, significant associations were found between parental occupational exposure to pesticides or solvents and the risk of attention deficit hyperactivity disorder in offspring. Prenatal occupational exposure to pesticides was significantly associated with motor development or cognition disorders in children. Furthermore, some evidence showed that metals might have a role in the development of autism spectrum disorders. Further studies need to identify the level of parental occupational exposures that can be significantly associated with NDDs. Moreover, utilizing standardized outcome and exposure scales is recommended to incorporate paternal, maternal, and parental as well as both prenatal and postnatal exposure in future studies.

Association between exposure to air pollutants and attention-deficit hyperactivity disorder (ADHD) in children: a systematic review and meta-analysis

Recent studies have reached mixed conclusions regarding the association between exposure to air pollutants and attention-deficit hyperactivity disorder (ADHD). We performed systematic review and meta-analysis to determine whether air pollutants were risk factors for the development of ADHD in children. We systematically searched databases for all relevant studies up to 2 July 2019. Together, the studies indicated that exposure to PAHs (risk ratio (RR): 0.98, 95% confidence interval (CI): 0.82-1.17), NOx (RR: 1.04, 95% CI: 0.94-1.15), and PM (RR: 1.11, 95% CI: 0.93-1.33) did not have any material relationship with an increased risk of ADHD. Heterogeneity of study data was low (I²: 2.7%, P = 0.409) for studies examining PAHs, but was substantial for NOx and PM (I²: 68.4%, P = 0.007 and I²: 60.1%, P = 0.014, respectively). However, these results should be interpreted with caution since the number of epidemiological studies investigating this issue were limited.

Air Pollution-Related Brain Metal Dyshomeostasis as a Potential Risk Factor for Neurodevelopmental Disorders and Neurodegenerative Diseases

Increasing evidence links air pollution (AP) exposure to effects on the central nervous system structure and function. Particulate matter AP, especially the ultrafine (nanoparticle) components, can carry numerous metal and trace element contaminants that can reach the brain in utero and after birth. Excess brain exposure to either essential or non-essential elements can result in brain dyshomeostasis, which has been implicated in both neurodevelopmental disorders (NDDs; autism spectrum disorder, schizophrenia, and attention deficit hyperactivity disorder) and neurodegenerative diseases (NDGDs; Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis). This review summarizes the current understanding of the extent to which the inhalational or intranasal instillation of metals reproduces in vivo the shared features of NDDs and NDGDs, including enlarged lateral ventricles, alterations in myelination, glutamatergic dysfunction, neuronal cell death, inflammation, microglial activation, oxidative stress, mitochondrial dysfunction, altered social behaviors, cognitive dysfunction, and impulsivity. Although evidence is limited to date, neuronal cell death, oxidative stress, and mitochondrial dysfunction are reproduced by numerous metals. Understanding the specific contribution of metals/trace elements to this neurotoxicity can guide the development of more realistic animal exposure models of human AP exposure and consequently lead to a more meaningful approach to mechanistic studies, potential intervention strategies, and regulatory requirements.

Coreduction methodology for immiscible alloys of CuRu solid-solution nanoparticles with high thermal stability and versatile exhaust purification ability

This study provides a coreduction methodology for solid solution formation in immiscible systems, with an example of a whole-region immiscible Cu–Ru system. Although the binary Cu–Ru alloy system is very unstable in the bulk state, the atomic-level well-mixed CuRu solid solution nanoparticles were found to have high thermal stability up to at least 773 K in a vacuum. The exhaust purification activity of the CuRu solid solution was comparable to that of face-centred cubic Ru nanoparticles. According to in situ infrared measurements, stronger NO adsorption and higher intrinsic reactivity of the Ru site on the CuRu surface than that of a pure Ru surface were found, affected by atomic-level Cu substitution. Furthermore, CuRu solid solution was a versatile catalyst for purification of all exhaust gases at a stoichiometric oxygen concentration.

This study provides a coreduction methodology for solid solution formation in immiscible systems, with an example of a whole-region immiscible Cu–Ru system.

Warming Increases Nitrous Oxide Emission from the Littoral Zone of Lake Poyang, China

Littoral wetlands are globally important for sustainable development; however, they have recently been identified as critical hotspots of nitrous oxide (N2O) emissions. N2O flux from subtropical littoral wetlands remains unclear, especially under the current global warming environment. In the littoral zone of Lake Poyang, a simulated warming experiment was conducted to investigate N2O flux. Open-top chambers were used to raise temperature, and the static chamber-gas chromatograph method was used to measure N2O flux. Results showed that the littoral zone of Lake Poyang was an N2O source, with an average flux rate of 8.9 μg N2O m−2 h−1. Warming significantly increased N2O emission (13.8 μg N2O m−2 h−1 under warming treatment) by 54% compared to the control treatment. N2O flux in the spring growing season was also significantly higher than that of the autumn growing season. In addition, temperature was not significantly related to N2O flux, while soil moisture only explained about 7% of N2O variation. These results imply that N2O emission experiences positive feedback effect on the ongoing warming of the climate, and abiotic factors (e.g., soil temperature and soil moisture) were not main controls on N2O variation in this littoral wetland.

Warming reduces the increase in N2O emission under nitrogen fertilization in a boreal peatland

Peatlands are known as N₂O sinks or low N₂O sources due to nitrogen (N) limitation. However, climate warming and N deposition can modulate this limitation, and little is known about the combinative effects of them on N₂O emission from boreal peatlands. In this study, experimental warming and N fertilization treatments were conducted at a boreal peatland in western Newfoundland, Canada. Contrary to previous studies on permafrost peatland and alpine meadows, the effect of warming treatment on N₂O flux was not detectable during the growing seasons of 2015 and 2016. The N fertilization treatment significantly increased the N₂O flux by 1.61 nmol m^-2 s^-1 due to increased N availability. Noticeably, warming reduced the effect of N fertilization treatment on N₂O flux with high significance in the middle growing season of 2015. This can be attributed to low N availability caused by stimulated vegetation growth in the warming treatment. In addition, the results showed that total nitrogen was the main control on N₂O emission under N fertilization, while dissolved organic carbon was the main driver under the combined treatment of warming and N fertilization. Due to elevated N₂O emissions under N deposition/fertilization, the contribution of N₂O to global warming and ozone depletion should not be ignored.

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.

Environmental factors influencing the link between childhood ADHD and risk of adult coronary artery disease

Yorbik et al. reported novel findings regarding a hypothesized relationship between childhood attention-deficit hyperactivity disorder (ADHD) and later risk for coronary heart disease in adulthood. The authors found that mean platelet volume (MPV), a marker of platelet reactivity and a presumable biomarker in patients with cardiovascular disease, was significantly elevated in children with ADHD compared to healthy controls. The mechanistic importance of this novel discovery remains unknown and warrants clarification. We have made the novel proposition that environmental exposure to the agricultural and combustion air pollutant, nitrous oxide (N₂O), may be an etiological contributor to neurodevelopmental disorders. Clinical studies suggest that N₂O may enhance platelet hyperaggregation, possibly via its biphasic role as an MAO inhibitor especially at trace levels of exposure or via the generation of oxidative stress. Therefore, this correspondence briefly details the hypothesis that altered biochemical profiles in neurodevelopmental disorders, derived from chronic environmental exposure to the agricultural and combustion air pollutant, N₂O, may promote coronary artery disease in adulthood.

Use of anthropogenic nitrogen fertilizers in agriculture is associated with per capita ethanol consumption

It has previously been demonstrated that emissions of the agricultural pollutant, nitrous oxide (N₂O), may be a confounder to the relationship between herbicide use and psychiatric impairments, including ADHD. This report attempts to extend this hypothesis by testing whether annual use of anthropogenic nitrogen-based fertilizers in U.S. agriculture (thought to be the most reliable indicator of environmental N₂O emissions) is associated with per capita ethanol consumption patterns, a behavior often comorbid with ADHD. State estimates of anthropogenic nitrogen fertilizers from the United States Geological Survey (USGS) were obtained for the years between 1987 and 2006. Our dependent variable was annual per capita ethanol consumption. Ethanol consumption was categorized as beer, wine, spirits, and all alcoholic beverages. Least squares dummy variable method using two-ways fixed effects was utilized. Among states above the 50th percentile in farm use of anthropogenic nitrogen for all years (i.e., agricultural states), a one log-unit increase in farm use of anthropogenic nitrogen fertilizers is associated with a 0.13 gallon increase in total per capita ethanol consumption (p<0.0125). No statistically significant association between farm use of anthropogenic nitrogen and per capita ethanol consumption was found in states below the 50th percentile in farm use of anthropogenic nitrogen. The new findings are in agreement with both behavioral human studies demonstrating a link between N₂O preference and alcohol and drug use history as well as molecular studies elucidating shared mechanisms between trace N₂O antinociception and alcohol-seeking related behaviors.

Air pollution and risk of hospitalization for epilepsy: the role of farm use of nitrogen fertilizers and emissions of the agricultural air pollutant, nitrous oxide

ABSTRACT The link between various air pollutants and hospitalization for epilepsy has come under scrutiny. We have proposed that exposure to air pollution and specifically the pervasive agricultural air pollutant and greenhouse gas, nitrous oxide (N2O), may provoke susceptibility to neurodevelopmental disorders. Evidence supports a role of N2O exposure in reducing epileptiform seizure activity, while withdrawal from the drug has been shown to induce seizure-like activity. Therefore, we show here that the statewide use of anthropogenic nitrogen fertilizers (the most recognized causal contributor to environmental N2O burden) is significantly negatively associated with hospitalization for epilepsy in all three pre-specified hospitalization categories, even after multiple pollutant comparison correction (p<.007), while the other identified pollutants were not consistently statistically significantly associated with hospitalization for epilepsy. We discuss potential neurological mechanisms underpinning this association between air pollutants associated with farm use of anthropogenic nitrogen fertilizers and hospitalization for epilepsy.

An update on anesthetics and impact on the brain

INTRODUCTION

While anesthetics are indispensable clinical tools and generally considered safe and effective, a growing concern over the potential neurotoxicity of anesthesia or specific anesthetic agents has called into question the safety of general anesthetics, especially when administered at extremes of age. Areas covered: This article reviews and updates research findings on the safety of anesthesia and anesthetics in terms of long-term neurotoxicity, with particular focus on postoperative cognitive dysfunctions, Alzheimer's disease and dementias, developing brain, post-operative depression and autism spectrum disorder. Expert opinion: Exposure to general anesthetics is potentially harmful to the human brain, and the consequent long-term cognitive deficits should be classified as an iatrogenic pathology, and considered a public health problem. The fact that in laboratory and clinical research only certain anesthetic agents and techniques, but not others, appear to be involved, raises the problem on what is the safest and the least safe anesthetic to maximize anesthesia efficiency, avoid occurrence of adverse events, and ensure patient safety. New trends in research are moving toward the theory that neuroinflammation could be the hallmark of, or could have a pivotal role in, several neurological disorders.

Abnormal sensory experiences, synaesthesia, and neurodevelopmental disorders

Preliminary evidence suggests that sensory processing may be affected in autism spectrum disorders (ASD). The purpose of this letter is to highlight a few recent studies on the topic and tie the findings to a recently identified epidemiological risk factor for ASD, principally environmental exposure to the air pollutant, nitrous oxide (N₂O). Animal studies have shown that trace levels of chronic N₂O exposure are thought to involve dynorphin opioid peptide release and altered serotonergic neurotransmission, both of which may elicit profound changes in consciousness and induce synaesthesia experiences. Future research investigating abnormal sensory sensitivity in ASD should consider environmental exposure to N₂O, which may induce the requisite neurochemical changes thought to underpin sensory dysregulation even at trace levels of exposure.

Environmental contributors to modulation of brain estrogen signaling and male gender bias in autism: A reply to the oral contraceptive use hypothesis by Strifert (2015)

Strifert has recently put forward an interesting hypothesis regarding the role of oral contraceptive (OC) use in mothers and risk of offspring autism spectrum disorder (ASD). First, the author reports that combined oral contraceptives (COCs), containing both estrogen and progesterone, were developed in the late 1950s and early 60s, which is a time-frame distinct from Leo Kanner's documentation of infantile ASD in 1943 that Strifert just briefly mentions. While this important temporal inconsistency of ASD origin does not invalidate the potential role of OC use in contributing to the rise of ASD, it does support the likely possibility of other environmental exposures at play. Second, the epigenetic basis of the hypothesis is that the endocrine-disrupting components (i.e., ethinylestradiol) of OC perturb estrogenic signaling in the fetal brain by triggering aberrant DNA methylation of the estrogen receptor β (ERβ) gene, and such methylation patterns may be imprinted to future generations and could theoretically increase subsequent ASD offspring risk. The premise of the hypothesis is challenged, however, with the recognition that MeCP2, a "reader" of DNA methylation sites, is not only associated with age-dependent alteration in ERβ in females but is also significantly reduced in ASD brain. Furthermore, Strifert does not clearly address how the OC hypothesis accounts for the male bias in ASD. Therefore, the purpose of this correspondence is to address these inconsistencies by proposing a hypothesis that challenges these points. That is, gestational exposure to the agricultural and combustion air pollutant, nitrous oxide (N₂O), may be a leading contributor to the development of an ASD phenotype. The mechanism undergirding this hypothesis suggests that compensatory estrogenic activity may mitigate the effects of fetal N₂O exposure and thereby confer a protective effect against ASD development in a sex-dependent manner (i.e., male bias in ASD).

Anesthetic agents, neurodevelopmental risk and the connection to bacterial infections

This short communication identifies a significant flaw in research investigating the neurodevelopmental consequences of general anesthesia exposure. We have identified that chronic environmental exposure to pervasive air pollutants that are also widely used as anesthetic agents, specifically nitrous oxide (N₂O), may contribute to the rising prevalence of neurodevelopmental disorders. Consistent with the emerging link between microbes and psychiatric illness risk, this epidemiological analysis extends our prior conclusions by proposing that such exposures may alter host immunity so as to enhance vulnerability to certain pathogenic microbes that have been implicated in neurodevelopmental disorders, including Pseudomonas aeruginosa and Clostridium difficile.

Exposure to ambient PM10 and nitrogen dioxide and ADHD risk: A reply to Min & Min (2017)

Min and Min (2017) conducted an epidemiological investigation that revealed further support of a link between exposure to air pollution and risk for attention-deficit hyperactivity disorder (ADHD) in childhood. We have previously reported that exposure to the agricultural and combustion pollutant, nitrous oxide (N₂O), may be a primary environmental trigger in the onset of neurodevelopmental disorders, like ADHD and autism spectrum disorders. In order to validate our prior work pointing to an association between farm use of nitrogen fertilizers and a severe ADHD phenotype, we have utilized a different statistical approach (i.e., Poisson regression methodology) including two-way fixed effects. The results reported in this correspondence indicate that for a one-log unit increase in the farm use of nitrogen fertilizers, hospitalization risk for ADHD and conduct disorders increases by a factor of 1.16 (p<0.017), which was a statistically significant increase in risk after multiple pollutant comparison correction. Exposure to PM10 and NOx in this analysis was not associated with an increased risk of hospitalization for ADHD and conduct disorder. We are able to validate our prior conclusions and, therefore, suggest that future analyses dedicated to improving the literature on the association between air pollution and risk of ADHD take into account environmental emissions of N₂O.

Commentary: 'Unhealthy diet,' nutrient status, and ADHD symptoms: a confounding role for environmental nitrous oxide exposure - reflections on Rijlaarsdam et al. (2016)

Rijlaarsdam et al. (2016) recently published their findings utilizing a longitudinal design showing that prenatal 'unhealthy diet' was positively associated with IGF2 DNA methylation at birth across both youth cohorts. However, only in the EOP youth was prenatal 'unhealthy diet' positively associated with ADHD symptoms presumably through IGF2 DNA hypermethylation. Rijlaarsdam et al.'s () choice to assess high fat and sugar diet with the Food Frequency Questionnaire (FFQ) may offer some indication as to prenatal nutrient status, as the foods identified by the FFQ in their study are relatively low in free choline. It has been shown that gestational choline deficiency in rats leads to hypermethylation of IGF2. Consistent with the literature describing an association between air pollution and cognitive neurodevelopmental impairment, the author of this commentary has previously proposed through empirical investigation that chronic environmental exposure to the trace levels of the pervasive air pollutant, nitrous oxide (N₂ O), may facilitate core features of neurodevelopmental disorders, like ADHD. Impaired acetylcholine synthesis in rats exposed to N₂ O has been shown, with a 53% reduction in [1-2H2,2-2H2] choline. Low-dose N₂ O exposure is also thought to stimulate central release of opioid peptides, like dynorphin, which play a role in significantly increasing food intake behavior and/or modulating sucrose intake. Taken altogether, these studies present a strong confounder to the interpretation made by Rijlaarsdam et al. () that prenatal 'unhealthy diet' may play a role in the onset of ADHD symptoms in youth with EOP conduct problems through induction of IGF2 DNA hypermethylation. While the 'unhealthy diet' may represent possible maternal nutrient deficiencies during gestation, it is also possible that exposure to air pollutants, particularly N₂ O, may not only directly reduce fetal cholinergic status thereby enhancing IGF2 DNA hypermethylation but may also significantly modulate maternal food intake behaviors (i.e. sucrose).

Propionic acid metabolism, ASD, and vitamin B12: Is there a role for environmental nitrous oxide?

Foley et al. (2014) published their findings in this journal on the role of prenatal exposure to propionic acid (PPA) and behavioral outcomes in treated rat pups. The authors show that PPA treated pups displayed subtle differences in behavior including nest seeking, novel object recognition, and locomotor activity. Others have previously proposed that PPA infusion in rat could represent a valid animal model of ASD since many of the diagnostic criteria for the disorder spectrum manifest under such conditions. A pathogenic makeover of gut microbiome to facilitate the growth of microbes capable of producing PPA, like Clostridia species, has been proposed as an infectious contributing etiology to the PPA model of ASD, however the reason for this pathogenic microbial overgrowth is not clear. This discussion highlights a previously identified novel environmental factor (i.e., nitrous oxide, N₂O) in the etiopathogenesis of ASD and related neuropathology and posits that altered PPA metabolism in ASD may represent a key manifestation of this particular exposure. Trace environmental exposure to N₂O may induce release of endogenous opioid peptides that have been shown to confer a virulence advantage to certain microbes, like Pseudomonas aeruginosa. Pathogenic overproduction of PPA in ASD may be a compensatory mechanism to curb this enhanced virulence potential. Therefore, future research on the PPA model of ASD should consider its role as a consequence of environmental exposure to N₂O.

Overlooking relevant confounders in the assessment of pesticides and human health: a reply to Mostafalou and Abdollahi

Mostafalou and Abdollahi (Arch Toxicol, 2016. doi: 10.1007/s00204-016-1849-x ) have recently conducted a review exploring human exposure to pesticides and systematically highlighting known toxic mechanisms from these exposures. Their review is extensive and appraises the literature on pesticide toxicity in a number of domains, including neurotoxicity and developmental toxicity. However, as important as it may be to understand the toxicological potential of these chemicals in humans and other species, the role of these chemicals as proxies for other environmental exposures should not be excluded. Recently, we published evidence suggesting use of the herbicide, glyphosate, may predict health care utilization for attention-deficit hyperactivity disorder (ADHD), a neurodevelopmental disorder that is characterized by cognitive impairments leading to attention deficits, impulsivity, and hyperactivity. Given that the finding appeared to be land-dependent, we concluded that glyphosate may be an instrumental variable that predicts severe ADHD mostly through its inseparableness from nitrogen fertilizers at a county level and increasing agricultural air emissions of the compound, nitrous oxide (N₂O). Since the WHO designates N₂O as an important modern health medicine, its environmental imprint is largely thought to be inconsequential in a human health context and, unfortunately, not worthy of further consideration. Our findings and subsequent review on the topic are not amenable to this complacency. We argue that future pesticide risk assessments be made more comprehensive insofar as identifying not only critical, direct routes of toxicity, as extensively reviewed by Mostafalou and Abdollahi (2016), but also indirect toxicological mechanisms such as the one presented in this correspondence.

Structural brain imaging correlates of ASD and ADHD across the lifespan: a hypothesis-generating review on developmental ASD-ADHD subtypes

We hypothesize that it is plausible that biologically distinct developmental ASD-ADHD subtypes are present, each characterized by a distinct time of onset of symptoms, progression and combination of symptoms. The aim of the present narrative review was to explore if structural brain imaging studies may shed light on key brain areas that are linked to both ASD and ADHD symptoms and undergo significant changes during development. These findings may possibly pinpoint to brain mechanisms underlying differential developmental ASD-ADHD subtypes. To this end we brought together the literature on ASD and ADHD structural brain imaging symptoms and particularly highlight the adolescent years and beyond. Findings indicate that the vast majority of existing MRI studies has been cross-sectional and conducted in children, and sometimes did include adolescents as well, but without explicitly documenting on this age group. MRI studies documenting on age effects in adults with ASD and/or ADHD are rare, and if age is taken into account, only linear effects are examined. Data from various studies suggest that a crucial distinctive feature underlying different developmental ASD-ADHD subtypes may be the differential developmental thinning patterns of the anterior cingulate cortex and related connections towards other prefrontal regions. These regions are crucial for the development of cognitive/effortful control and socio-emotional functioning, with impairments in these features as key to both ASD and ADHD.