Prospective analysis of strength in spinal muscular atrophy

Spinal muscular atrophy is a genetic disorder of the motor neurons that cau ses profound hypotonia, severe weakness, and often fatal restrictive lung d isease. Patients with spinal muscular atrophy present a spectrum of disease from the most severe infantile-onset type, called Werdnig-Hoffmann disease (type 1), associated with a mortality rate of up to 90%, to a late-onset m ild form (type 3), wherein patients remain independently ambulatory through out adult life. Although many clinicians agree that patients with spinal mu scular atrophy lose motor abilities with age, it is unknown whether progres sive weakness occurs in all patients with spinal muscular atrophy. we prese nt here results of the first prospective study of muscle strength in patien ts with spinal muscular atrophy. There was no loss in muscle strength as de termined by a quantitative muscle test during the observation period. Howev er, motor function diminished dramatically in some patients with spinal mus cular atrophy. Explanations for this loss of function could not be determin ed from our data. Decrease in motor function could be caused by factors oth er than loss of strength. Therefore, it is not clear from our results wheth er spinal muscular atrophy is a neurodegenerative disease. We conclude that treatment trials in spinal muscular atrophy should be designed with consid eration of the natural history of strength and motor function in this disor der.