SMN1 and proximal spinal muscular atrophy: For example, splicing regulator dysfunction is associated with FSHD or DM1, while defects in survival of motor neuron 1 (SMN1), which plays a central role in the biogenesis of small nuclear ribonucleoproteins (snRNPs), can lead to spinal muscular atrophy (SMA1, MIM253300)15,16.