Theory of Mind impairment in childhood narcolepsy type 1: a case-control study

Narcolepsy type 1 is a central disorder of hypersomnolence characterized by excessive daytime sleepiness, cataplexy and other rapid eye movement sleep-related manifestations. Neurophysiological studies suggest that narcolepsy type 1 patients may experience impairment in emotional processing due to structural and functional changes in limbic structures and associated areas. However, the only study exploring narcolepsy behavioural responses found no impairment in the ability to recognize emotions, possibly due to compensatory mechanisms. The present study was designed to fill this gap in the literature by investigating the behavioural impairment related to emotional processing focusing on an advanced socio-cognitive skill, namely Theory of Mind, in paediatric narcolepsy type 1 patients. Twenty-two narcolepsy type 1 children and adolescents (six female; age range: 8.0-13.5) and 22 healthy controls matched for age and sex (six female; age range: 8.9-13.0) underwent a neuropsychological evaluation to assess socio-economic status, verbal abilities, working memory, social anxiety and Theory of Mind via a verbal task (i.e. Strange Stories task) and a visual task (i.e. Silent Films). Narcolepsy type 1 patients were also evaluated for disease severity. Patients exhibited impairment in Theory of Mind skills, as assessed both through both verbal (controls median = 8; patients median = 5; P = 0.009) and visual tasks (controls median = 8; patients median = 6; P = 0.003), compared to healthy controls. Correlation analyses showed that verbal and visual Theory of Mind was negatively related to narcolepsy severity (ρ = -0.45, P = 0.035 and ρ = -0.52, P = 0.012), and daytime sleepiness (ρ = -0.48, P = 0.025 and ρ = -0.45, P = 0.038). Our study shows a selective impairment in the Theory of Mind domain in children and adolescents with narcolepsy type 1. In addition, our results highlight a link between symptom severity and Theory of Mind, suggesting that lower Theory of Mind levels are associated with higher symptom severity. Further, longitudinal studies are needed to disentangle the direction of this relation and to disambiguate if narcolepsy severity impaired children's Theory of Mind or if Theory of Mind skills modulate the severity of narcolepsy symptoms by providing a greater ability to avoid cataplexy.