SMN1 and proximal spinal muscular atrophy: In light of our observations about the lack of neurodegeneration at days 3 to 5 in adult smn-1 mutants (Fig. 1I), our data suggest that in the absence of wild-type levels of SMN-1 protein, muscle cell defects occur before motor neuron degeneration, a phenomenon that may have implications in the design of therapeutic approaches for SMA.