SMN1 and proximal spinal muscular atrophy: According to the first report of SMN1 by Lefebvre et al. [12], complete absence of SMN1 (or homozygous SMN1 deletion) was found in 226 (98.7%) of 229 patients with SMA irrespective of their clinical subtypes, and an intragenic SMN1 mutation (a small mutation in SMN1) was found in 3 (1.3%) of these 229 patients.