Sleep in children with Tourette syndrome: The relation with tic severity and executive functioning

Introduction: Tourette syndrome (TS) is a neurodevelopmental condition characterised by motor and vocal tics, which change in form and frequency throughout one’s life. Issues with sleep have consistently been reported in TS, but current understanding is incomplete due to limited use of validated sleep scales; conflicting findings from clinic-based sleep assessments; and a lack of sleep actigraphy studies, which are needed to provide naturalistic, objective sleep data. Additionally, links between sleep and executive functioning are unexamined in this population, despite evidence showing the negative knock-on effects that poor sleep can have on executive development. This research project addressed these gaps in the literature through three original studies. Study 1: Study 1 was a systematic review synthesising findings from all existing studies reporting objective sleep data in TS. No actigraphy studies were identified for inclusion, meaning knowledge of objective sleep behaviour in TS was based exclusively on polysomnographic sleep assessments. To examine the impact of co-occurring ADHD, an ADHD comparison group was included, and data were pooled according to diagnosis: TS-only (N = 108), TS+ADHD (N = 79), ADHD-only (N = 316), and controls (N = 336). Meta-analyses identified significantly poorer sleep in TS based on objective sleep parameters, including increased sleep onset latency and reduced sleep efficiency, which were present even in the absence of ADHD. Study 2: Study 2 used a cross- sectional design to understand the nature of sleep disturbances in children with TS and links to everyday executive functioning, using validated scales and open-ended questions for qualitative insights. Children and adolescents with TS (n = 136) had significantly more sleep disturbances compared to typically-developing controls (n = 101), which were associated with higher tic severity and more everyday executive difficulties. TS-specific sleep issues were reported by parents, including tics preventing sleep and tiredness increasing tics. Study 3: Study 3 used an intensive longitudinal design, collecting two weeks of 24-hour sleep actigraphy data, daily diaries to track fluctuations in tics, neuropsychological tasks to assess executive functioning, and questionnaires to examine everyday behaviour. This provided the longest period of sleep monitoring in a TS population to date. Mixed effects modelling using N = 476 nights of data from 34 children aged between 8 and 12 years with TS (n = 12) and without TS (n = 22) identified objectively poorer sleep in the TS group based on several actigraphic sleep parameters, including increased sleep onset latency, increased time in bed, and reduced sleep efficiency. Particular difficulties were highlighted with sleep initiation in children with TS. This was not significantly related to higher self-report tic severity at bedtime, but two-thirds of parents in the TS group stated that tics can prevent their child from falling asleep at night. Despite matched performance on executive tasks, children with TS displayed significantly more everyday executive difficulties, which were also associated with lower actigraphic sleep efficiency and greater parent-report sleep disturbances. Conclusions: Together, the findings from these three studies provide evidence of substantial sleep disturbances in children with TS, based on both subjective and objective measures. There is a need for increased focus on sleep in the clinical management of TS, including sleep measures and interventions tailored specifically to this population. Findings from this thesis need to be considered in light of sampling limitations and the lack of validation studies using actigraphy in TS. Future research is needed to substantiate the current findings and to determine directionality between sleep, tics, and executive functioning in TS.