The objective of this study was to construct a composite score of global function that will discriminate among people with Spinal Muscular Atrophy (SMA). 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 Six-Minute Walk Test as percent predicted normal distance. A principal component analysis was performed on the correlation matrix for the 3 percentage scores. 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. This combination of measures broadens the spectrum of ability that can be quantified in Type 2 and 3 SMA patients.
