The Role of Temperament and Broader Autism Phenotype in the Prediction of Toddlerhood Externalising and Internalising Symptoms

Background:  Autism Spectrum Disorder (ASD) is the term used to describe a cluster of neuro-developmental conditions comprising social and communication impairments and the presence of restricted patterns of behaviours and interests. Co-morbid Internalising and Externalising symptoms are prevalent and often have greater negative impact on functioning than do the core ASD symptoms themselves. Significant heterogeneity is apparent across every facet of ASD, both in terms of core and co-morbid symptoms. However, factors that may account for such heterogeneity remain poorly understood. Given  the substantial body of research showing both the positive and negative impacts of temperament on social, emotional, and behavioural outcomes outside the context of ASD, it seems clear that research on temperament in the context of ASD may hold significant potential for informing our understanding of the variability inherent in individuals’ developmental trajectories and outcomes.

Objectives:  

To explore the extent to which Internalising and Externalising symptoms may vary as a function of temperamental differences among young children between 2- and 3-years of age (when ASD is often diagnosed), and in conjunction with the Broader Autism Phenotype (BAP) and specific ASD symptom presentation.

Methods:  

Mothers of 60 toddlers completed the Short Temperament Scale for Toddlers and the Behavior Assessment System for Children when toddlers were aged between 2 and 3 years. Thirty children had an older sibling diagnosed with ASD (BAP) and around half of them met criteria for an ASD diagnosis (BAP-ASD) by 3 years of age. The older sibling of 30 children did not have ASD. All children were assessed for cognitive level using the Mullen Scales of Early Learning and children in the BAP group were assessed for ASD symptoms using the Autism Diagnostic Observation Schedule (ADOS). 

Results:  

Toddlers in the BAP group had more Externalising, t(45)=2.98, p=.005 (Cohen’s d=.89) and Internalising Problems, t(45)=2.54, p=.015, d=.76, than those without a sibling with ASD. There was also the suggestion of more Externalising Problems among the BAP-ASD compared to the BAP-non ASD subgroup, t(21)=1.32, p=.203, d=.58, but there was no evidence of subgroup differences on Internalising Problems, t(21)=.51, p=.619,  d=22. While no differences on global Easy/Difficult Temperament were detected between the BAP and control group, t(35.8)=.12, p=.908, d=.04, there was a suggestion of more difficult temperament among the BAP-ASD subgroup, t(21)=1.67, p=.109, d=73. For the whole sample, however, more difficult temperament was significantly associated with both externalising (r=.41, p<.01) and internalising symptoms (r=.58, p<.01) and the associations remained significant after controlling for the effect of BAP and cognitive level.

Conclusions:  

This study replicated previous findings suggesting higher rates of Internalising and Externalising symptoms in individuals with the BAP, extending to demonstrate that this is already the case by toddlerhood. Furthermore, our findings suggest that temperament predicted both internalising and externalising traits over and above the influence of cognitive level, BAP status and ASD traits. Further longitudinal research is necessary in order to explore the directionality of the effect and to capitalise on the possibilities afforded through study of the construct of temperament in infants and children with ASD.