Assessing ambulation in patients with Duchenne muscular dystrophy (DMD) below 4 years old (yo) is challenging with traditional outcomes, yet crucial for therapeutic development. Using the Syde wearable sensor, designed to accurately measure ambulation in daily life, we previously obtained primary endpoint qualification of SV95C (stride velocity 95th centile) by the European Medicines Agency, in ambulant DMD older than 4 yo.
The robustness and sensitivity of SV95C for assessing ambulation in subjects below 4 yo were evaluated in the ActiLiege-Next study. Patients were asked to wear two ankle sensors daily for the first 3 months and then for 1 month every 3 months, and age-matched controls for 1 month every 6 months.
Twenty-eight patients were enrolled (mean age ± standard deviation [range]: 34.7 ± 9.1 months [16.1-47.4]), and twenty-seven healthy boys (32.0 ± 10.6 months [12.8-47.8]). Five patients were on steroids before or upon enrolment, and as of August 2025 seven initiated steroids during follow-up. All but one patients (N=27) and all controls (N=27) showed good baseline compliance. SV95C reliability was excellent with intraclass correlation coefficients ≥0.97 for patients and >0.90 for controls at all timepoints. Mean SV95C at baseline was significantly higher in controls than in patients (p<0.001). Longitudinal data showed a stronger SV95C increase for controls than patients at 12 months: mean change from baseline was 0.51m/s for controls (n=17), and 0.24m/s for steroid-naïve patients (n=12), respectively. For the 7 patients starting steroids during follow-up, median SV95C increase was 0.17m/s/year before and 0.47m/s/year after starting steroids. This suggests that SV95C can distinguish patients from healthy boys and quantify steroids effect in small cohorts.
These results validate and support the use of SV95C as a functional motor outcome and a measure of treatment effectiveness in all ambulant DMD including those younger than 4 yo.