Survival of Motor Neuron 1 gene (SMN1, MIM#600354), located on chromosome 5q13.2 was initially identified as the childhood SMA causative gene (Lefebvre et al., 1995), soon after mapping this autosomal recessive disorder to chromosome 5q (Brzustowicz et al., 1990). Here, SMN1 is linked to proximal spinal muscular atrophy.