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Comparative Study

Prospective cohort study of spinal muscular atrophy types 2 and 3

Petra Kaufmann et al. Neurology. .

Abstract

Objective: To characterize the natural history of spinal muscular atrophy type 2 and type 3 (SMA 2/3) beyond 1 year and to report data on clinical and biological outcomes for use in trial planning.

Methods: We conducted a prospective observational cohort study of 79 children and young adults with SMA 2/3 who participated in evaluations for up to 48 months. Clinically, we evaluated motor and pulmonary function, quality of life, and muscle strength. We also measured SMN2 copy number, hematologic and biochemical profiles, muscle mass by dual x-ray absorptiometry (DXA), and the compound motor action potential (CMAP) in a hand muscle. Data were analyzed for associations between clinical and biological/laboratory characteristics cross-sectionally, and for change over time in outcomes using all available data.

Results: In cross-sectional analyses, certain biological measures (specifically, CMAP, DXA fat-free mass index, and SMN2 copy number) and muscle strength measures were associated with motor function. Motor and pulmonary function declined over time, particularly at time points beyond 12 months of follow-up.

Conclusion: The intermediate and mild phenotypes of SMA show slow functional declines when observation periods exceed 1 year. Whole body muscle mass, hand muscle compound motor action potentials, and muscle strength are associated with clinical measures of motor function. The data from this study will be useful for clinical trial planning and suggest that CMAP and DXA warrant further evaluation as potential biomarkers.

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Figures

Figure 1
Figure 1. Association between motor function (Expanded Hammersmith Functional Motor Scale [HFMSE] score) and maximal compound motor action potential (CMAP) area under the curve (AUC) (mV × msec) at baseline
Figure 2
Figure 2. Mean change in Expanded Hammersmith Functional Motor Scale (HFMSE) score over time estimated using a repeated measures analysis of covariance model with time treated as a categorical variable
Error bars indicate 1 SEM. Mean changes are plotted for spinal muscular atrophy (SMA) 2 and SMA 3 combined, SMA 2 only, and SMA 3 only.
Figure 3
Figure 3. Mean change in forced expiratory vital capacity (FVC) (percentage of predicted normal) over time estimated using a repeated measures analysis of covariance model with time treated as a categorical variable
Error bars indicate 1 SEM. Mean changes are plotted for spinal muscular atrophy (SMA) 2 and SMA 3 combined, SMA 2 only, and SMA 3 only.
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