Preprint: naturally regenerating muscle fibres express utrophin, complicating readouts in Duchenne therapy trials

A preprint posted on bioRxiv describes work defining how utrophin expression is regulated during skeletal muscle regeneration, with direct implications for the interpretation of trials testing utrophin-based therapies for Duchenne muscular dystrophy (DMD).

DMD is an X-linked, lethal muscle-wasting disease caused by loss-of-function variants in the dystrophin gene. Utrophin is a structural paralogue of dystrophin that can partially compensate for dystrophin deficiency when expressed at the muscle fibre membrane (sarcolemma). Several therapeutic programmes aim to elevate utrophin as a mutation-agnostic approach — applicable regardless of which specific pathogenic variant a patient carries. However, the preprint's authors report that utrophin is also naturally upregulated at the sarcolemma of regenerating myofibres — new muscle fibres produced in response to ongoing muscle damage, which is characteristic of dystrophic muscle.

This creates a confounding factor: if a trial measures utrophin levels at the sarcolemma as a surrogate biomarker for therapeutic activity, it may be difficult to distinguish drug-induced utrophin elevation from the natural elevation associated with muscle regeneration. The authors characterise the temporal relationship between utrophin expression and complementary regeneration markers, which may help future trial designs incorporate appropriate controls or co-measured biomarkers. The preprint has not yet been peer-reviewed. The work is relevant to researchers working in neuromuscular genetics, translational dystrophinopathy research, and those involved in designing or interpreting biomarker strategies for DMD trials.