Spinal muscular atrophy (SMA), the leading genetic cause of infant mortality, is characterized by the specific degeneration of spinal motor neurons caused by the mutation in the SMN1 gene (Pearn et al, 1978; Pearn, 1980; Burglen et al, 1995; Lefebvre et al, 1995). This evidence concerns the gene SMN1 and spinal muscular atrophy.