The so-called “classic” SMA, accounting to ~94–96% of cases, is caused by large deletions within the survival motor neuron 1 gene (SMN1, HGNC:11117, OMIM:*600354) or by a gene conversion from SMN1 to its paralogue, survival motor neuron 2 gene (SMN2, HGNC:11118, OMIM *601627) [6]. This evidence concerns the gene SMN2 and proximal spinal muscular atrophy.