Development of Italian centile curves for the North Star Ambulatory Assessment and timed items

Centile curves may improve the interpretation of motor outcomes in specific populations. This study aimed to develop Italian age-specific centile curves for NSAA, rise-from-floor velocity (RFFV), and 10-meter walk/run velocity (10MWRV) in boys with Duchenne muscular dystrophy (DMD) and to assess their agreement with existing UK reference curves. Data from 627 patients (5080 assessments) with an age between 3-18 years were extracted from the Italian DMD Registry. GAMLSS models were used to estimate centile curves. Agreement with UK data (restricted to ages 5-16 years and who are actively on steroids) was evaluated using SDS deviation and percentile coverage analyses. NSAA scores peaked at approximately 6 years; RFFV and 10MWRV peaked at 5 years, then progressively declined. The Italian cohort showed small deviations from the UK centiles (all p<0.001): mean SDS values were significantly different across all outcomes, and age was significantly associated with SDS deviation through both linear and quadratic effects. The Italian centile curves extend reference data to wider age ranges. Available for both general and steroid-treated patients, they support clinical trials and real-world practice. The minor differences observed, especially in timed velocities, highlight the need for future international harmonisation.