The Rett Syndrome Gross Motor Scale–Dutch Version (RSGMS-NL) Can Reliably Assess Gross Motor Skills in Dutch Individuals with Rett Syndrome

Aim: The Rett Syndrome Gross Motor Scale (RSGMS) is an observational measurement, assessing gross motor skills in individuals with Rett syndrome. A Dutch version is lacking. The current study aims to translate and cross-culturally adapt the original RSMGS to Dutch and assess its inter-rater and intra-rater reliability. Design: Translation and cross-cultural adaptation were performed in concordance with internationally accepted guidelines. A pretest was performed, and expert validation was assured. Video data of three girls with Rett syndrome was independently assessed by 27 physiotherapists via an online webinar to measure inter-rater reliability. Additionally, videos of 17 individuals with Rett syndrome were scored twice by two raters to assess intra-rater reliability. The reliability of the total score, the three subscale scores and the new items were analyzed using Intraclass Correlation Coefficients (ICC). Results: Good comprehensibility and expert validation of the RSMGS-NL was achieved, and four items were added to the original scale. Inter-rater reliability for the total score was excellent (ICC 0.97, 95% CI 0.89–0.99), and good to perfect inter-rater reliability for the three subscales; Sitting, Standing & walking and Challenge was found (ICC values 1.0 (95% CI 0), 0.98 (95% CI 0.91–0.99) and 0.82 (95% CI 0.93–0.99) respectively). The intra-rater reliability was excellent for the total test score (ICC 0.98, 95% CI 0.97–0.99) and good to excellent for the subscale scores (ICC values 0.87 (95% CI 0.75–0.94), 0.99 (95% CI 0.98–1.0) and 0.97 (95% CI 0.95–0.99) respectively). The four new items (Standing to sitting, walking down a slope, ascending the stairs, descending the stairs) showed good to excellent intra-rater reliability. Conclusion: The RSGMS-NL is a reliable measure of gross motor skills in Dutch individuals with Rett syndrome.