Irritability in boys with autism spectrum disorders: an investigation of physiological reactivity.

BACKGROUND Irritability in people with autism spectrum disorders (ASD) is common and impairing, yet its mechanisms remain understudied. We investigated symptom reporting and mechanisms of irritability in ASD, focusing on the relation between irritability and physiological stress responses. METHODS Forty-seven unmedicated boys with high-functioning ASD (hfASD) and 23 typically developing boys aged 10-16 years completed a psychosocial stress test. Changes in cortisol, heart rate and heart rate variability throughout the test were recorded. Self- and parent-reported measures of irritability were obtained. Irritability symptom reporting in the hfASD group was compared to two groups of boys without ASD: highly irritable boys (severe mood dysregulation, SMD; n = 40) and healthy-control boys (HC; n = 30). RESULTS Boys with hfASD scored significantly higher on irritability than HC boys, and they reported a pattern of irritability symptoms closely resembling that of boys with SMD. The internal consistency of irritability in hfASD was high by parent- and self-report. Although boys with hfASD showed significant stress-induced changes in cortisol and heart rate, those who rated themselves as highly irritable had lower cortisol levels throughout the test compared to those low on irritability. Participants rated as highly irritable by their parents showed blunted cortisol and heart rate responses to stress. The effects of irritability on heart rate, but not cortisol, were accounted for by trait anxiety. CONCLUSIONS Irritability can be measured reliably in hfASD and is associated with distinct biological responses to stress.