SMN1 and proximal spinal muscular atrophy: Spinal muscular atrophy (SMA) is a rare progressive genetic neuromuscular disorder affecting spinal motor neurons, caused by defects in both copies of the SMN1 gene, leading to degeneration of alpha motor neurons in the anterior horn of the spinal cord (Masson et al., 2021; Day et al., 2022; Verhaart et al., 2017).