Spinal muscular atrophy functional composite score: A functional measure in spinal muscular atrophy

Introduction: With clinical trials underway, our objective was to construct a composite score of global function that could discriminate among people with spinal muscular atrophy (SMA). Methods: Data were collected from 126 participants with SMA types 2 and 3. Scores from the Hammersmith Functional Motor Scale-Expanded and Upper Limb Module were expressed as a percentage of the maximum score and 6-minute walk test as percent of predicted normal distance. A principal component analysis was performed on the correlation matrix for the 3 percentage scores. Results: The first principal component yielded a composite score with approximately equal weighting of the 3 components and accounted for 82% of the total variability. The SMA functional composite score, an unweighted average of the 3 individual percentage scores, correlated almost perfectly with the first principal component. Conclusions: This combination of measures broadens the spectrum of ability that can be quantified in type 2 and 3 SMA patients.