Emotion dysregulation as a key mediator between neurodevelopmental features and sleep difficulties: distinct underlying mechanisms in adults with ADHD, autism, and co-occurring autism-ADHD

Emotion dysregulation and sleep difficulties are highly prevalent transdiagnostic features in autism and Attention Deficit Hyperactivity Disorder (ADHD). Yet the differential mechanisms underlying these dimensions remain poorly understood, particularly in adults. This study investigates the specific profiles of emotion dysregulation (ED) and sleep difficulties in autistic adults, adults with ADHD, adults with co-occurring autism and ADHD, and controls, and examines two reciprocal mediation models linking neurodevelopmental features, ED, and insomnia symptom severity. 858 adults (autism, n = 163; ADHD, n = 235; co-occurring autism and ADHD, n = 186; neurotypical controls, n = 274) completed validated self-report questionnaires assessing core neurodevelopmental symptoms, alexithymia, ED, sleep quality, insomnia severity, and chronotype. Between-group comparisons were conducted using General Linear Models controlling for age and gender. Within-group mediation analyses were performed using bias-corrected bootstrap methods. Autistic adults and adults with co-occurring autism and ADHD displayed the highest overall ED, driven primarily by alexithymia (particularly difficulties identifying and describing feelings) and reduced use of cognitive reappraisal. Sleep efficiency was specifically reduced in autistic adults and in those with co-occurring autism and ADHD. Adults with ADHD showed a distinct profile characterized by affective lability, emotional over-reactivity, prolonged sleep latency, and evening chronotype. Adults with co-occurring autism and ADHD showed the most severe profiles across most domains. Mediation analyses revealed that across all clinical groups, ED mediated the relationship between core neurodevelopmental features and insomnia severity, with alexithymia emerging as an additional indirect predictor in autism and in the co-occurring group. All measures relied on self-report. The sample was predominantly female, which limits generalizability to men and gender-diverse individuals. The cross-sectional design prevents causal inference, and longitudinal studies are needed to confirm the directionality of these relationships. These findings identify ED as a transdiagnostic mediating pathway between neurodevelopmental features and sleep difficulties, while highlighting condition-specific mechanisms. Specifically, in ADHD, core symptoms may foster emotional hyperarousal and lability that interferes with sleep initiation, whereas in autism, alexithymia-related difficulties in attending to and appraising internal signals may sustain poorly integrated interoceptive states incompatible with consolidated sleep. The study was approved by the Ethics Committee of the University of Strasbourg (CER#2023–37).