Background <p>Phelan-McDermid syndrome (PMS) is a rare genetic condition caused by SHANK3 gene haploinsufficiency. Individuals with PMS often exhibit developmental delays, language deficits, and neurological and psychiatric symptoms that frequently overlaps with autism. Sleep disturbances and sensory reactivity differences are also highly prevalent in this population, yet their relationship remains unexplored. Given prior research in autism, which has identified links between sensory sensitivities and sleep difficulties, this study aims to investigate the association between sensory processing differences and sleep disturbances in children with PMS.</p> Methods <p>We used 2 standardised questionnaires: The Children’s Sleep Habit Questionnaire (CSHQ) and the Child Sensory Profile 2 (SP-2) to measure sleep behaviour and sensory reactivity differences in families with children with PMS (n=40) (median age of caregivers = 42.95, median age of children = 10.52 years). We performed descriptive statistics, spearman correlations and stepwise regressions to examine relationships between sensory reactivity and sleep quality.</p> Results <p>Findings revealed significant correlations between sleep difficulties and sensory sensitivity, sensory registration, and sensory seeking. Further analysis of specific sensory modalities identified correlations between sleep difficulties and touch, movement and oral processing. Stepwise regression demonstrated that sensory seeking and oral sensitivity were significant predictors of sleep disturbances, explaining 19.9% and 34.6% of the variance, respectively.</p> Conclusions <p>This study highlights a significant relationship between sensory reactivity differences and sleep disturbances in children with PMS. Findings suggest that sensory processing differences, particularly oral sensitivity and sensory seeking, contribute to sleep difficulties. These insights underscore the need for targeted interventions to improve sleep quality in individuals by addressing sensory sensitivities.</p>