Building the repertoire of measures of walking in Rett syndrome

Background: The repertoire of measures of walking in Rett syndrome is limited. This study aimed to determine measurement properties of a modified two-minute walk test (2MWT) and a modified Rett syndrome-specific functional mobility scale (FMS-RS) in Rett syndrome. Methods: Forty-two girls and women with Rett syndrome (median 18.4 years, range 2.4-60.9 years) were assessed for clinical severity, gross motor skills, and mobility. To measure walking capacity, 27 of this group completed a 2MWT twice on two different assessment days. To assess walking performance, the FMS-RS was administered to the total sample of parents (n=42) on two occasions approximately one week apart. Results: There were negative correlations between clinical severity and 2MWT (r=-0.48) and FMS-RS (r=-0.60-0.66). There were positive correlations between gross motor skills and mobility and 2MWT (r=0.51, 0.43) and FMS-RS (r=0.71-0.93, 0.74-0.94), respectively. Test-retest reliability for the 2MWT was good with high intraday and interday correlations (ICC=0.86-0.98). For the 2MWT, the standard error of measurement was 13.8 m and we would be 95% confident that changes greater than 38 m would be greater than within subject error. There was good test-retest reliability for all three distances on the FMS-RS (ICC=0.94-0.99). Conclusions: Walking capacity as measured by the 2MWT showed expected but limited relationships with measures of different constructs, providing some support for concurrent validity. Walking performance as measured with the FMS-RS was more strongly consistent with other clinical measures supporting its concurrent validity. Test-retest reliability was good for both the FMS-RS and the 2MWT. Therefore, these measures have the potential to be used in clinical practice and research.