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Objective: Irritability in children with autism spectrum disorder (ASD) is prominent and often leads to distress to both autistic children and their families. However, the nature of irritability in autism and the difference from nonautistic children have rarely been examined. This study aimed to investigate the clinical characteristics of irritability in autism, and to compare the symptom profiles with those of disruptive mood dysregulation disorder (DMDD) in nonautistic children. Methods: Fifty-six children aged 7-17 years (mean age 10.36 ± 3.05) were recruited into this study (21 with DMDD, 21 with high-functioning autism [hfASD], and 14 healthy volunteers [HV]). Their parents completed the Aberrant Behavior Checklist-Irritability (ABC-I) subscale and the Strengths and Difficulties Questionnaire (SDQ) parent report form. The ABC-I subscale was analyzed as a whole and broken into subsets (ABC-I-Irritability, ABC-I-Agitation, and ABC-I-Crying). The symptom profiles of irritability and the association with psychosocial difficulties were compared between groups. Results: The ABC-I-Irritability scores of children with hfASD closely matched to those of children with DMDD. In addition, both DMDD and hfASD groups could be differentiated from HV group in five of the six items except "depressed mood." However, in the ABC-I-Agitation scale, children with DMDD, but not hfASD, had higher scores in "Aggressive to other patients and staff" and "Stamps feet while banging objects or slamming doors" than HV. Regarding psychosocial outcomes, irritability in children with DMDD and hfASD were associated with emotional problems as measured by the SDQ. Moreover, irritability in DMDD was associated with conduct problems, and the hfASD group exhibited the similar trend. Conclusions: Symptom profiles of irritability and the associated emotional and conduct problems in children with hfASD were similar to those of DMDD in the nonautistic population. Future studies are warranted to explore the underlying neurophysiological mechanisms of irritability between autistic and nonautistic children for further insight into the nature of irritability in autism.

Background: Autism spectrum condition and attention-deficit/hyperactivity disorder (ADHD) are associated with a range of physical health conditions. The aim of this study was to examine the etiological components contributing to co-occurring physical health conditions in autism and ADHD., Methods: In this nationwide Child and Adolescent Twin Study in Sweden, we analyzed data from 10,347 twin pairs aged 9 and 12. Clinical diagnoses of autism, ADHD, and physical health conditions were identified through the Swedish National Patient Register. Subclinical phenotypes of autism and ADHD were defined by symptom thresholds on a standardized parent-interview, the Autism-Tics, ADHD, and Other Comorbidities inventory. Associations between physical health conditions and autism/ADHD phenotypes were examined using generalized estimating equations. Bivariate twin models were applied to estimate the extent to which genetic and environmental risk factors accounted for physical health comorbidities., Results: Similar patterns of association with physical health conditions were found in clinical and subclinical autism/ADHD, with odds ratios ranging from 1.31 for asthma in subclinical ADHD to 8.03 for epilepsy in clinical autism. The estimated genetic correlation (r a ) with epilepsy was 0.50 for clinical autism and 0.35 for subclinical autism. In addition, a modest genetic correlation was estimated between clinical autism and constipation (r a  = 0.31), functional diarrhea (r a  = 0.27) as well as mixed gastrointestinal disorders (r a  = 0.30). Genetic effects contributed 0.86 for mixed gastrointestinal disorders in clinical ADHD (r a  = 0.21). Finally, subclinical ADHD shared genetic risk factors with epilepsy, constipation, and mixed gastrointestinal disorders (r a  = 0.30, 0.17, and 0.17, respectively)., Limitations: Importantly, since medical records from primary care were not included in the registry data used, we probably identified only more severe rather than the full range of physical health conditions. Furthermore, it needs to be considered that the higher prevalence of physical health conditions among autistic children and children with ADHD could be associated with the increased number of medical visits., Conclusions: Shared genetic effects contribute significantly to autism and ADHD phenotypes with the co-occurring physical health conditions across different organ systems, including epilepsy and gastrointestinal disorders. The shared genetic liability with co-occurring physical health conditions was present across different levels of autism and ADHD symptom severity., (© 2023. The Author(s).)

Although highly heritable, environment also contributes to the etiology of autism spectrum disorder (ASD), with several specific environmental factors previously suggested. A registry-linked population-based twin cohort of 15,701 pairs (586 individuals with an ASD diagnosis), was established within the Child and Adolescent Twin Study in Sweden. Participants were evaluated for autistic symptoms at age 9 using the Autism-Tics, ADHD and other Comorbidities parental interview. A series of binary cut-offs indicated whether participants scored over various ASD symptom percentiles. Three early medical factors previously associated with ASD, beyond familial confounding (low birth weight, congenital malformations and perinatal hypoxia), were summed up creating an individual cumulative exposure load. A series of unconditional logistic regressions between all individuals and conditional regressions within twin pairs were performed for each outcome and exposure level. Between all individuals increasing cumulative early exposure loads were associated with increasing risk of ASD diagnosis (OR 3.33 (95%CI 1.79-6.20) for three exposures) and autistic symptoms (ranging from OR 2.12 (1.57-2.86) for three exposures at the 55th symptom percentile cut-off to OR 3.39 (2.2-5.24) at the 95th). Within twin pairs, the association between three exposures and an ASD diagnosis remained similar, but not statistically significant (OR 2.39 (0.62-9.24)). Having a higher load of early cumulative exposure was consistently associated with autistic symptoms after adjusting for familial confounding and sex (OR 3.45 (1.66-7.15) to OR 7.36 (1.99-27.18)). This study gives support to the cumulative stress hypothesis of ASD, and the dimensional model regarding environmental exposures, after adjustment for familial confounding., (© 2022. The Author(s).)

Lay Abstract: Neurological disorders, such as epilepsy and cerebral palsy, have been reported to occur among individuals with autism beyond chance and may have an impact on daily living across the lifespan. Although there has been research investigating neurological disorders in autism, the findings are not always conclusive. Previous summaries of existing studies have not evaluated the full range of neurological disorders. This study aimed to comprehensively explore the neurological problems appearing in autism to provide updated information that is needed for better healthcare and support in this population. We looked at already published studies focusing on risk or frequency of neurological disorders in autism. Our results suggest that individuals with autism are more likely than the general population to have a range of neurological disorders, including epilepsy, macrocephaly, hydrocephalus, cerebral palsy, migraine/headache, and inborn abnormalities of the nervous system. In order to provide individualized healthcare and support of high quality to individuals diagnosed with autism, health care professionals and other support providers need to be attentive to neurological complications. To further improve our understanding about the link between autism and neurological disorders, future research should follow the neurological health of children who are diagnosed with or are at increased likelihood of autism.

This study used a twin cohort to investigate the association of autism spectrum disorder (ASD) and autistic traits with somatic health. A total of 344 twins (172 pairs; mean age 15.56 ± 5.62 years) enriched for ASD and other neurodevelopmental conditions were examined. Medical history and current physical problems were collected with a validated questionnaire to determine twin's somatic health. The Social Responsiveness Scale (SRS-2) was used to measure the participant's severity of autistic traits. Identified somatic health issues with significant within-twin pair differences were tested in relation to both ASD diagnosis and autistic traits in a co-twin control model. Twins with ASD exhibited more neurological and immunological health problems compared to those without ASD (p = 0.005 and p = 0.004, respectively). The intra-pair differences of neurological conditions and SRS-2 score were significantly correlated in monozygotic twins differing for autism traits (r = 0.40, p = 0.001), while the correlation was not found for immunological problems. In addition, a conditional model for analysis of within-twin pair effects revealed an association between neurological problems and clinical ASD diagnosis (Odds ratio per neurological problem 3.15, p = 0.02), as well as autistic traits (β = 10.44, p = 0.006), after adjusting for possible effects of co-existing attention deficit hyperactivity disorder and general intellectual abilities. Our findings suggest that neurological problems are associated with autism, and that non-shared environmental factors contribute to the overlap for both clinical ASD and autistic traits. Further population-based twin studies are warranted to validate our results and examine in detailed the shared genetic and environmental contributions of neurological problems and ASD.