Upper limb disease evolution in exon 53 skipping eligible patients with Duchenne muscular dystrophy

Objective To understand the natural disease upper limb progression over 3 years of ambulatory and non‐ambulatory patients with Duchenne muscular dystrophy (DMD) using functional assessments and quantitative magnetic resonance imaging (MRI) and to exploratively identify prognostic factors. Methods Forty boys with DMD (22 non‐ambulatory and 18 ambulatory) with deletions in dystrophin that make them eligible for exon 53‐skipping therapy were included. Clinical assessments, including Brooke score, motor function measure (MFM), hand grip and key pinch strength, and upper limb distal coordination and endurance (MoviPlate), were performed every 6 months and quantitative MRI of fat fraction (FF) and lean muscle cross sectional area (flexor and extensor muscles) were performed yearly. Results In the whole population, there were strong nonlinear correlations between outcome measures. In non‐ambulatory patients, annual changes over the course of 3 years were detected with high sensitivity standard response mean (|SRM| ≥0.8) for quantitative MRI‐based FF, hand grip and key pinch, and MFM. Boys who presented with a FF27% were able to bring a glass to their mouth and retained this ability in the following 3 years. Ambulatory patients with grip strength >35% of predicted value and FF