Spinal muscular atrophy (SMA) is genetic and progressive, caused by large bi-allelicdeletions in the SMN1 gene, or the association of a large deletion and a nullvariant.1 SMA leads to the degeneration of theanterior horn motor neurons and the motor nuclei of some cranial nerves.1,2 Only in rare cases have two single nucleotideschanges been reported to be causative of the disease. This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.