The SMN protein is encoded by two genes,SMN1and its homologous geneSMN2, both located on chromosome 5.1, 4, 5, 6In approximately 96% of SMA-5q patients, the disease is caused by a homozygous deletion of exons 7 and 8 of theSMN1, or in some cases, just exon 7.1In about 4% of cases, there is a deletion in one allele and a point mutation in the other allele. This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.