SMN1 and proximal spinal muscular atrophy: Spinal muscular atrophy (SMA) is a severe neuromuscular disease caused by loss‐of‐function mutations in the survival of motor neuron 1 (SMN1) gene, which encodes the SMN protein.1 Its neighbouring centromeric SMN2 gene is intact in all patients but cannot fully compensate for the loss of SMN1, due to the alternative splicing and exclusion of exon 7 from most of its transcript.2, 3