The cumulative impact of attention deficit hyperactivity disorder, autism and intellectual disability for young people

Abstract Background Neurodevelopmental conditions frequently co‐occur. The aim of this paper was to determine whether there is a cumulative association between (1) the number of neurodevelopmental conditions, specifically hyperkinetic disorder (hereafter referred to as attention deficit hyperactivity disorder), autism spectrum disorder (hereafter referred to as autism) and intellectual disability, and (2) behavioural and socio‐emotional problems and the level of clinician‐rated functioning for young males and females. Methods In this cross‐sectional study, diagnostic information, caregiver‐rated behavioural and socio‐emotional data (as conceptualised by the Strengths and Difficulties Questionnaire) and clinician‐rated functioning scores (as conceptualised by the Children's Global Assessment Scale) were extracted from electronic patient records for 2768 young people aged 3–17 years (mean = 11.55, SD = 3.46). All data were extracted at baseline, that is, at the time the young person was diagnosed with attention deficit hyperactivity disorder, autism and/or an intellectual disability. Ordinal regression analyses tested associations between the number of neurodevelopmental conditions met (i.e. 1, 2 or 3) and behavioural and socio‐emotional outcomes and functioning. Results After controlling for age and biological sex, the number of neurodevelopmental conditions was associated with higher levels of inattention/hyperactivity and peer problems, lower levels of prosocial behaviour and poorer clinician‐rated functioning. Although these findings were consistent for males, a cumulative association was not identified for females, except for clinician‐rated functioning. Conclusions For young people, the presence of multiple neurodevelopmental conditions may have a cumulative impact across domains, but this may differ between males and females.