The larger the number of SMN2 copies, the lesser the severity of SMA symptoms[85-87].The SMN2 gene significance for thedevelopment of a more mild form of spinal muscular atrophy is confirmed byasymptomatic cases when the number of SMN2 gene copies issufficiently large (four or more) in individuals homozygous for deletion of theSMN1 gene [88]. This evidence concerns the gene SMN2 and proximal spinal muscular atrophy.