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Autism and ADHD are associated with difficulties with Executive Functions (EFs), but the prevalence and nature of these difficulties in early development is not well understood. In this longitudinal study, 107 children with a family history of autism and/or ADHD (FH-autism/ADHD), and 24 children with No-FH-autism/ADHD completed multiple EF tasks (5 at age 2 years, 7 at age 3 years). Parents reported on their child’s autism- (Q-CHAT at age 2, SRS-2 at age 3), and ADHD-related traits (CBCL DSM-ADHD scale, both ages). Compared to the No-FH-autism/ADHD group, the FH-autism/ADHD group showed lower scores on simple EFs (involving response inhibition, and holding in mind) at ages 2 and 3. Exploratory analysis linked FH-autism specifically with lower Executive Attention (top-down attentional control) at age 2, and the combination of FH-autism and FH-ADHD with lower Complex EF (involving selectively deploying responses, or updating information) at age 3. Three-year-olds’ Simple EF scores were negatively associated with ADHD-related traits. Complex EF scores were negatively associated with autism traits (before correcting for multiple comparisons). Toddlers with a family history of autism and/or ADHD may benefit from interventions to support simple EF development, whilst those already showing autistic traits may benefit from support with more-complex EF skills.

The aim of this study was to explore the associations between temperamental reactivity and regulation and the emergence of anxiety traits in a longitudinal sample of infants enriched for later ASD. Parents of 143 infants who were at high- and low-risk for ASD rated their child’s temperament traits when they were 9, 15 and 24 months old; they rated anxiety and ASD traits when they were 36 months old. The findings suggest that behavioural inhibition may be an early predictor of later anxiety in children with and without ASD and that lower levels of effortful control in children who later develop ASD may contribute to the higher expression of anxiety within this population.

Sleep problems in Autism Spectrum Disorder (ASD) emerge early in development, yet the origin remains unclear. Here, we characterise developmental trajectories in sleep onset latency (SOL) and night awakenings in infants at elevated likelihood (EL) for ASD (who have an older sibling with ASD) and infants at typical likelihood (TL) for ASD. Further, we test whether the ability to gate tactile input, using an EEG tactile suppression index (TSI), associates with variation in SOL and night awakenings. Parent-reported night awakenings and SOL from 124 infants (97 at EL for ASD) at 5, 10 and 14 months were analyzed using generalized estimating equations. Compared to TL infants, infants at EL had significantly more awakenings and longer SOL at 10 and 14 months. The TSI predicted SOL concurrently at 10 months, independent of ASD likelihood status, but not longitudinally at 14 months. The TSI did not predict night awakenings concurrently or longitudinally. These results imply that infants at EL for ASD wake up more frequently during the night and take longer to fall asleep from 10 months of age. At 10 months, sensory gating predicts SOL, but not night awakenings, suggesting sensory gating differentially affects neural mechanisms of sleep initiation and maintenance.

Background Attention‐Deficit/Hyperactivity Disorder (ADHD) is linked to strengths in creative problem‐solving amongst school‐aged children and adults. In contrast, autism (which frequently co‐occurs with ADHD) is associated with lower generativity, and perseverative responses during problem‐solving. Little is known about how ADHD and autism traits—or broader heritable autism and ADHD phenotypes—associate with problem‐solving skills in early childhood. Methods 129 UK 2‐ and 3‐year‐olds (exploratory dataset) and 74 Swedish 3‐year‐olds (confirmatory dataset) with and without a family history (FH) of ADHD and autism, completed a problem‐solving task. Parents reported on their 3‐year‐olds’ ADHD and autism traits using the Child Behaviour Checklist and Social Responsiveness Scale‐2. FH group differences in problem‐solving performance were tested using ANOVA (exploratory dataset, FH‐autism and FH‐ADHD as fixed factors) and t‐test (confirmatory and combined datasets split by FH‐ADHD). Linear regressions of problem‐solving success on autism/ADHD traits were run in both samples. Results Compared with peers with no FH‐ADHD, children with FH‐ADHD showed higher problem‐solving success at 2 (partial ω2 = 0.106) and 3 years (partial ω2 = 0.045) in the exploratory dataset. In the confirmatory dataset, a FH‐ADHD‐and‐autism group trended towards higher success scores compared with a no‐FH‐ADHD group (comprising FH‐autism‐only and no‐FH ADHD‐or‐autism sub‐groups) but scores were only significantly higher for children with FH‐ADHD‐and‐autism when compared with children with no FH‐ADHD‐or‐autism (gs = 0.977). ADHD (but not autism) traits were positively associated with problem‐solving performance in the exploratory (β = 0.212, p = 0.031) and combined samples (β = 0.173, p = 0.024). Effects were a consistent direction and magnitude, but not significant, in the confirmatory sample alone (β = 0.201, p = 0.103). Conclusions Considering a child's family history alongside their neurodivergent traits may help to identify their likely strengths, and how to access them: Children with ADHD traits and/or a family history of ADHD are likely to have an aptitude for generative problem‐solving when presented with highly motivating, ecologically valid challenges. In this study 129 UK 2‐ and 3‐year‐olds, and 74 Swedish 3‐year‐olds, with and without a family history of ADHD and autism, completed a problem‐solving task. Our results show that children with ADHD traits and/or a family history of ADHD are likely to have an aptitude for generative problem‐solving when presented with highly motivating, ecologically valid challenges.

Background Most research on early outcomes in infants with a family history (FH) of autism has focussed on categorically defined autism, although some have language and developmental delays. Less is known about outcomes in infants with a FH of attention deficit hyperactivity disorder (ADHD). Methods Infants with and without a FH of autism and/or ADHD, due to a first‐degree relative with either or both conditions, were recruited at 5 or 10 months. Three year outcomes were characterised using latent profile analysis (LPA) across measures of cognitive ability, adaptive functioning and autism, ADHD and anxiety traits (n = 131). We additionally ran an LPA using only autism and ADHD measures, and the broader LPA in an independent cohort (n = 139) and in both cohorts combined (n = 270). Results A Low Developmental Level + High Behavioural Concerns class had elevated autism, ADHD and anxiety scores, low cognitive and adaptive function, and included all but one child with autism. A Low Developmental Level + Typical Behaviour class had average cognitive ability and typical behaviour but low adaptive function. A Typical Developmental Level + Some Behavioural Concerns class had average cognitive and adaptive function but slightly elevated behaviour scores. A High Developmental Level + Typical Behaviour class had above average cognitive ability and typical behaviour. All four LPAs identified classes characterised by combinations of either, or both, Low Development Level and elevated behaviour scores, as well as a typically developing class. No classes had elevated autism or ADHD traits in isolation. Conclusions Some infants with a FH of autism or ADHD have atypical developmental and behavioural outcomes, but do not show strong autism or ADHD traits in isolation. The field needs to recalibrate aims and methods to embrace the broader transdiagnostic pattern of outcomes seen in these infants. We used a broad range of outcome measures to identify the ‘natural categories’ of early atypical outcome in infants with family history of autism or ADHD. Some infants with a family history of autism or ADHD have neurodevelopmental profiles characterised by combinations of either, or both, low developmental level and atypical behaviour but not elevated autism or ADHD traits in isolation. The field needs to adopt a transdiagnostic approach in the study of early development in autism and ADHD in order to develop fit‐for‐purpose developmental models and translational opportunities.

Autism and ADHD are characterised by atypical sensory responsivity, and this may be driven by alterations in the balance of cortical excitation to inhibition (E/I). Studies early in development are required to establish when sensory responsivity differences emerge and whether they predict later neurodevelopmental condition outcomes. We utilised data from a prospective longitudinal cohort of infants with and without a family history (FH) of autism and/or ADHD (N = 151; 55% male, 83% white). We extracted electroencephalography (EEG) metrics of E/I balance at 5, 10 and 14 months; the aperiodic exponent of the slope of the power spectrum (‘1/f’). Models estimated latent growth curves of parent-reported hyper and hypo-responsivity between 10 – 36 months. Analyses tested associations between developmental trajectories of FH, sensory responsivity, parent-rated neurodevelopmental traits at 3 years and E/I balance. We coded and entered binary variables indexing FH-autism and FH-ADHD in the same model, which allowed us to test for effects of one form of FH whilst adjusting for the impact of the other. Results showed that FH-autism was associated with greater increases in parent-reported hyper-responsivity between 10–36 months (over and above the effects of FH-ADHD), and in univariate models for hyper-responsivity only, the intercept and the slope of hyper-responsivity were positively associated with both autistic and ADHD traits at age 3 years. However, in joint models which included hypo-responsivity, associations between hyper-responsivity and autistic and ADHD traits became non-significant. In these joint models, FH-ADHD was associated with steeper increases in hypo-responsivity (over and above the effects of FH-autism). Higher hypo-responsivity at 10-month baseline was associated with both autistic and ADHD traits at 3 years. A steeper slope of hypo-responsivity predicted ADHD traits at 3 years. Males displayed higher baseline hypo-responsivity. Aperiodic exponent values at 5 and 10, but not 14 months, were associated with hyper-responsivity. Results suggest a dissociation in the type of sensory responsivity associated with a family history of autism as compared to a family of ADHD, and that hypo-responsivity in infancy may be an indicator of later autism and ADHD outcomes. However, better measurement of each domain is required to draw strong conclusions as many hypo-responsivity items overlapped with autistic and ADHD traits. Alterations in E/I balance may contribute to early differences in sensory responsivity but further research is required to determine the directionality of effects.

We investigated infant’s manual motor behaviour; specifically behaviours crossing the body midline. Infants at elevated likelihood of Autism Spectrum Disorder (ASD) and/or Attention Deficit Hyperactivity Disorder (ADHD) produced fewer manual behaviours that cross the midline compared to infants with a typical likelihood of developing these disorders; however this effect was limited to 10-month-olds and not apparent at age 5 and 14 months. Although, midline crossing did not predict ASD traits, it was related to ADHD traits at 2 years of age. We rule out motor ability and hand dominance as possible explanations for this pattern of behaviour, positing that these results may be a consequence of multisensory integration abilities, and the neurobehavioural shift period, in the first year of life.

Backgrounds Atypicalities in tactile processing are reported in autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) but it remains unknown if they precede and associate with the traits of these disorders emerging in childhood. We investigated behavioural and neural markers of tactile sensory processing in infants at elevated likelihood of ASD and/or ADHD compared to infants at typical likelihood of the disorders. Further, we assessed the specificity of associations between infant markers and later ASD or ADHD traits. Methods Ninety-one 10-month-old infants participated in the study ( n = 44 infants at elevated likelihood of ASD; n = 20 infants at elevated likelihood of ADHD; n = 9 infants at elevated likelihood of ASD and ADHD; n = 18 infants at typical likelihood of the disorders). Behavioural and EEG responses to pairs of tactile stimuli were experimentally recorded and concurrent parental reports of tactile responsiveness were collected. ASD and ADHD traits were measured at 24 months through standardized assessment (ADOS-2) and parental report (ECBQ), respectively. Results There was no effect of infants’ likelihood status on behavioural markers of tactile sensory processing. Conversely, increased ASD likelihood associated with reduced neural repetition suppression to tactile input. Reduced neural repetition suppression at 10 months significantly predicted ASD (but not ADHD) traits at 24 months across the entire sample. Elevated tactile sensory seeking at 10 months moderated the relationship between early reduced neural repetition suppression and later ASD traits. Conclusions Reduced tactile neural repetition suppression is an early marker of later ASD traits in infants at elevated likelihood of ASD or ADHD, suggesting that a common pathway to later ASD traits exists despite different familial backgrounds. Elevated tactile sensory seeking may act as a protective factor, mitigating the relationship between early tactile neural repetition suppression and later ASD traits.

Autism Spectrum Disorder (ASD) is a heritable neurodevelopmental condition that is characterised by social communication impairments, restricted and repetitive behaviours, and sensory anomalies. Anxiety is one of the marked co-occurring psychiatric conditions in individuals with ASD and the underlying mechanism of this co-occurrence has not been fully understood. This is because studies have focused on mid-childhood or adolescence when the interplay between genetic and environmental risk factors make it harder to disentangle the overlap between symptoms of anxiety and ASD. Temperament traits in infancy, especially behavioural inhibition (BI) which is a temperament trait that is involved in the aetiology of the childhood anxiety in the general population, may be an informative target to explore roots of this interplay prior to the consolidation of both disorders. The current thesis employs a multi-method approach to investigate the association between BI and anxiety in two cohorts of infants at high- and low-familial risk for ASD. Participants of Chapter 2 and 3 were drawn from the second phase of the British Autism Study of Infant Siblings (BASIS; this study is complete and outcome grouping is available). In Chapter 2, longitudinal associations between parent-reported BI, effortful control, anxiety and ASD traits were examined using cross-lagged panel models. In Chapter 3, temperament traits were measured during the Autism Observational Schedule for Infants (AOSI; 15 months) by using a new observational coding scheme. Further analyses investigated whether observed individual differences relate to AOSI scores, anxiety and ASD traits at 36 months. In Chapter 4, factor scores for social and non-social BI were generated at 24 months by using observational, parent-reported and global ratings of BI. In Chapter 5, the associations between parental and child anxiety and ASD trait was examined. Participants of Chapter 4 and 5 were drawn from the third phase of the BASIS project. Both parent-reported and observed BI was associated with higher levels of anxiety but not ASD traits. Parental characteristics (anxiety and ASD traits) were related to child characteristics. Overall, these findings suggest that similar to the general population, BI is involved in the aetiology of early emerging anxiety traits in toddlers at risk of ASD. The consistent association between BI and anxiety across chapters suggest that there may be separate developmental pathways for anxiety and ASD. So, BI may provide a translational target for pre-emptive interventions.

Autism is frequently associated with difficulties with top-down attentional control, which impact on individuals’ mental health and quality of life. The developmental processes involved in these attentional difficulties are not well understood. Using a data-driven approach, 2 samples (N = 294 and 412) of infants at elevated and typical likelihood of autism were grouped according to profiles of parent report of attention at 10, 15 and 25 months. In contrast to the normative profile of increases in attentional control scores between infancy and toddlerhood, a minority (7–9%) showed plateauing attentional control scores between 10 and 25 months. Consistent with pre-registered hypotheses, plateaued growth of attentional control was associated with elevated autism and ADHD traits, and lower adaptive functioning at age 3 years.