Fig. 1

Data collection overview. Data from imaging and questionnaire/cognition components were collected concurrently between twin pairs (i.e., while one twin underwent brain imaging, their co-twin completed the mental health/behavioural questionnaire and cognitive testing). An early morning saliva sample was collected at home and brought to the session, along with any available baby teeth. Hair, blood, and urine samples were obtained during the session, with faecal samples and accelerometry measures of sleep behaviour collected at home. Neuroimaging and key phenotypes, saliva and hair samples were collected at sessions 1 and 2.