Cortisol circadian rhythms and response to stress in children with autism

Background: Autism is a severe neurodevelopmental disorder characterized by impairment in communication, social interaction, repetitive behaviors and difficulty adapting to novel experiences. The Hypothaiamic-Pituitary-Adreno-cortical (HPA) system responds consistently to perceived novel or unfamiliar situations and can serve as an important biomarker of the response to a variety of different stimuli. Previous research has suggested that children with autism may exhibit dysfunction of the HPA system, but it is not clear whether altered neuroendrocrine regulation or altered responsiveness underlies the differences between children with and without autism. In order to provide preliminary data concerning HPA regulation and responsiveness, we compared circadian rhythms and Methods: Circadian rhythms of cortisol were estimated in children with (N = 12) and without (N = 10) autism via analysis of salivary samples collected in the morning, afternoon and evening on 2 consecutive days. HPA responsiveness was assessed by examining the time course of changes in salivary cortisol in response to a mock MRI. Results: Both groups showed expected circadian variation with higher cortisol concentration in morning than in the evening samples. The children with autism, but not typical children, showed a more variable circadian rhythm as welt as statistically significant elevations in cortisol, following exposure to a novel, nonsocial stimulus. Conclusions: The results suggest that children with autism process and respond idiosyncratically to novel and threatening events resulting in an exaggerated cortisol response. (c) 2005 Elsevier Ltd. All rights reserved.