Investigating Biological, Psychological and Social factors of early symptom emergence in ASD and ADHD: A longitudinal 'high-risk' study.

In human development, it is now known that an interaction between biological (genetic risks, brain and neurocognitive development) and environmental factors over the life course affects both typical and atypical developmental trajectories. Understanding the nature of this interplay is essential, particularly in children who are at increased risk of neurodevelopmental disorders.

Autism spectrum disorder (ASD) is a moderate-to-highly heritable disorder (Messinger et al., 2015; Szatmari et al., 2016). ASD and attention deficit hyperactivity disorder (ADHD) have also been found to have high rates of co-occurrence (Russell, Rodgers, Ukoumunne & Ford, 2014). There is research which highlights shared risk factors concerning genetic (Smoller, 2013) and environmental (Ronald, Pennell & Whitehouse, 2011) risks for the disorders, and possible mechanisms of resilience common to those at 'high-risk' for ASD and ADHD (Johnson, 2012).

Given the heritability of the disorders, studying an infant with a first-degree sibling with a diagnosis of ASD or ADHD provides unique insight into the developmental trajectory of the disorders. This can help to identify common and distinct mechanisms leading to the early emergence of symptoms of the two disorders. It can also advance knowledge about subclinical traits in the broader Autism phenotype (BAP) (Ozonoff et al., 2011). These advantages advocate the high-risk sibling design that is being utilised in the British Autism Study of Infant Siblings, Studying Autism and ADHD Risks (BASIS STAARS), under Principal Investigators Professor Mark Johnson and Professor Tony Charman (see http://staars.org).

The current cohort of this phase of BASIS STAARS includes 100 high-risk ASD, 80 high-risk ADHD and 40 low-risk control infants and toddlers. The children are seen in the laboratory at 5, 10, 14, 24 and 36 months, and engage in a range of experimental and behavioural observation assessments. These include eye tracking, EEG, parent-child interaction (PCI), and the Autism Diagnostic Observation Schedule (ADOS), to name a few. During laboratory visits, parents engage in interviews such as the Vineland. Parents are also asked to complete questionnaires that measure infant behaviours, older sibling (proband) symptom levels and the family environment.

Therefore, this project proposes to exploit the high-risk longitudinal design within BASIS STAARS, to investigate the emergence of early symptoms and development of ASD and ADHD. By adopting a multi-disciplinary approach, this research will aim to investigate the biological, psychological and social factors underlying causal mechanisms of ASD and ADHD. Furthermore, this research proposes to investigate the presence of sub-clinical traits by exploring the nature of the BAP in the infant and toddler cohort, other siblings and parents of the probands.

It would be interesting to shed light on areas that are lacking in existing literature with this project. For example, investigating the role of multi-sensory integration in aspects of early social communicative development in high-risk individuals (and how this may differ in ASD and ADHD). Additionally, investigating neurocognitive features that are specific to the development of the respective disorders would be of interest to draw conclusions regarding their high co-occurrence.

In summary, by utilising the aforementioned multi-disciplinary methods, it is possible to explore mechanisms underlying the heterogenous causal factors of ASD and ADHD, as separate and/or co-occurring entities. Furthermore, investigating the nature of these interactions over time will elucidate the underlying factors for resilience to the emergence of clinical traits of the disorders. Insight into the nature of these interactions in early development is important for the progression of early interventions and in order to help identify individuals at greatest risk, whom would benefit most from additional support.