Spinal muscle atrophy (SMA) is a devastating disease that is characterized by loss of motor neuron function and subsequent muscle weakness and atrophy. The disease results from deletion of survival of motor neuron 1 (SMN1) and SMN protein deficiency.
In humans, a duplication SMN1, SMN2 results in a truncated SMN protein; however, the number of SMN2 copies inversely correlates to disease severity. Disease onset occurs shortly after birth following a short period of normal muscle function.
In this issue of the Journal of Clinical Investigation, Umrao Monani and colleagues at Columbia University demonstrate in a mouse model that the timing of SMN depletion during development is critical to the pathogenesis of disease. Depletion of SMN in the early neonatal period resulted in an SMA-like phenotype, while depletion of SMN in mature mice had no effect.
In an accompanying Commentary, Kathryn Swoboda of the University of Utah discusses the implications of a temporal requirement of SMN for optimization of SMN repletion-based therapy.