Abstract
The current study used a multifaceted approach to assess whether children with ASD have a distinctive diurnal rhythm of cortisol that differentiates them from typically developing (TD) peers and whether sub-groups of ASD children can be identified with unique diurnal profiles. Salivary cortisol was sampled at four time points during the day (waking, 30-min post-waking, afternoon, and evening) across three days in a sample of 36 children with autism spectrum disorder (ASD) and 27 typically developing (TD) peers. Between-group comparisons on both mean levels and featural components of diurnal cortisol indicated elevated evening cortisol and a dampened linear decline across the day in the ASD group. No differences were evident on the cortisol awakening response (CAR). Group-based trajectory modeling indicated that a subgroup (25%) of ASD children demonstrated an attenuated linear decline while the cortisol trajectory of the second subgroup was indistinguishable from that of the TD group. Intraclass correlations indicated that, when aggregated across days, cortisol measures were generally stable over the interval assessed. There were few significant relations between cortisol measures or sub-groups and measures of stress, temperament, and symptoms. Results encourage follow-up studies to investigate the functional significance, heterogeneity and longer-term stability of diurnal cortisol profiles in children with ASD.