Rett syndrome: establishing a novel outcome measure for walking activity in an era of clinical trials for rare disorders

Abstract

Background: Rett syndrome is a pervasive neurological disorder with impaired gait as one criterion. This study investigated the capacity of three accelerometer-type devices to measure walking activity in Rett syndrome. Methods: Twenty-six participants (mean 18 years, SD 8) wore an Actigraph, ActivPAL and StepWatch Activity Monitor (SAM) during a video-taped session of activities. Agreement was determined between step-counts derived from each accelerometer and observation. Repeatability of SAM-derived step counts was determined using pairs of one-minute epochs during which the same participant was observed to walk with the same cadence. Results: The mean difference (limit of agreement) for the Actigraph, ActivPAL and SAM were −41 (SD 33), −16 (SD 21) and −1 (SD 16) steps/min, respectively. Agreement was influenced by a device/cadence interaction (p < 0.001) with greater under-recording at higher cadences. For SAM data, repeatability of step-count pairs was excellent (intraclass correlation coefficient 0.91, 95% CI 0.79–0.96). The standard error of measurement was 6 steps/min and we would be 95% confident that a change ≥17 steps/min would be greater than within-subject measurement error. Conclusions: The capacity of the SAM to measure physical activity in Rett syndrome allows focus on participation-based activities in clinical practice and clinical trials.

Implications for Rehabilitation

• Many girls and women with Rett syndrome are able to walk on their own or with assistance but with altered movement patterns.

• Validated measures of physical activity, such as step counts, have potential to monitor function during daily life.

• Compared with other forms of accelerometer-type devices, such as ActiGraph and ActivPAL, the StepWatch Activity Monitor (SAM) measured step counts with good accuracy and repeatability.

• The capacity of the SAM to measure physical activity in Rett syndrome allows focus on participation-based activities in clinical practice and clinical trials.

• Outcome measure
• physical activity
• Rett syndrome
• walking

Acknowledgements

We would like to thank the girls and women with Rett syndrome together with their families and other caregivers who participated in this study. We also acknowledge Zachary Nielsen and Nikki Newton for their assistance with the database.

Declaration of interest

The current study had access to the infrastructure of the Australian Rett Syndrome Database housed at the Telethon Kids Institute. We acknowledge the Australian Paediatric Surveillance Unit and the Rett Syndrome Association of Australia who facilitated case ascertainment in Australia. Major aspects of the Australian Rett Syndrome Research Program have been funded by National Institutes of Health and NHMRC funding. The Australian Rett Syndrome Research Program is currently supported by a NHMRC project grant [#1004384] and a NHMRC program grant [#572742]. Professor Helen Leonard’s current funding is from an NHMRC Senior Research Fellowship [#572568]. The manufacturers of the devices had no role in the design, conduct or analyses of this study.

The current study received a HeART grant from the International Rett Syndrome Foundation. The authors declare that there is no conflict of interest.