SMN1 and proximal spinal muscular atrophy: While the exact mechanisms linking these changes in the motor unit to the clinical manifestations of SMA remain unclear, diminished levels of SMN protein are recognized as a pivotal factor (Lefebvre et al., 1995; Lefebvre et al., 1997; Reilly et al., 2024; Lorson et al., 2010; Hua et al., 2011; Mercuri et al., 2022).