The relationship between chronic stress, co-occurring conditions, sleep, and autistic features including severity using hair cortisol concentration.

BACKGROUND AND OBJECTIVE: Autism is highly heterogeneous and reliance on behavioural assessments alone may not provide sufficient insight into the unique characteristics of autistic individuals. Biomarkers, like hair cortisol concentration (HCC), may help unravel mechanisms underlying clinical variation in autism and support diagnostic measures, especially in young children who may not be able to effectively communicate their distress. We examined the relationship between HCC and autistic traits along with commonly co-occurring conditions including sleep disturbances in autistic children compared to non-autistic children. METHODS: We conducted a cross-sectional analysis utilising data from the Australian Autism Biobank comprising clinical and biological samples from Australian children aged 2-17 years. Primary analysis included multivariable linear regression analyses to identify significant associations with HCC after controlling for key sociodemographic covariates, including child's intelligence quotient (IQ). RESULTS: The study included 307 autistic children, 158 non-autistic siblings, and 124 unrelated non-autistic children. The commonly reported co-occurring conditions were global developmental delay (8.5 %), intellectual disability (6.1 %), and otitis media (6.1 %). Higher severity of autistic traits and in particular social affect issues, co-occurring attention-deficit/hyperactivity disorder (ADHD), internalising, and maladaptive behaviours were significantly associated with lower normalised HCC. Higher sleep anxiety and IQ were associated with higher HCC. Regarding sociodemographic factors, older age and higher family income were associated with lower HCC. CONCLUSION: The findings indicate the clinical value of HCC as a viable biomarker to identify subgroups based on co-occurring medical and mental health conditions. Further research to elucidate the link to individual and family/environmental factors as potential sources of stress is needed to offer targeted supports.