Over 95% of SMA patients have a homozygous deletion in the SMN1(Survival Motor Neuron1) gene located on chromosome5, while inversions, reading frame shift mutations, missense mutations,nonsense mutations, and splicing site changes occur only in a few cases[80, 81].A full list of known mutations of theSMN1 gene is available in the Leiden Open Variation Database(http://www.dmd.nl/nmdb2/home.php?select_ db=SMN). This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.