Dystrophin isoform deficiency and upper-limb and respiratory function in Duchenne muscular dystrophy

To investigate the associations between mutations expected to differentially affect Dp140 expression and long-term trajectories of respiratory and upper-limb motor outcomes in Duchenne muscular dystrophy (DMD).

In a retrospective analysis of population-based longitudinal data from three real-world and natural history data sources, individuals with DMD aged 5 years to 18 years were subdivided according to the predicted effects of the participants' DMD mutation on dystrophin isoform expression (group 1, Dp427 absent, Dp140/Dp71 present; group 2, Dp427/Dp140 absent, Dp71 present).

A total of 459 participants were studied, with upper-limb outcomes assessed in 71 (27 in group 1 and 44 in group 2) and forced vital capacity percentage predicted (%pred) assessed in 434 (224 in group 1 and 210 in group 2). Mean grip strength %pred was on average 7.1 percentage points lower in group 2 than in group 1 (p = 0.03). Mean pinch strength %pred was on average 9.2 percentage points lower in group 2 than in group 1 (p = 0.04). Mean forced vital capacity %pred was on average 4.3 percentage points lower in group 2 than in group 1 (p = 0.01).

In individuals with DMD, DMD mutations predicted to affect Dp140 expression were associated with more severe trajectories of respiratory and upper-limb motor outcomes.