Spinal muscular atrophy (SMA) is a hereditary neurodegenerative disease with an average prevalence and birth incidence of 1-2 and 8 per 100.000 persons, respectively. SMA is categorized in 4 types depending on clinical features, ranging from severe phenotypes with poor prognosis (~6-12 months) to milder phenotypes. However, most SMA cases belong to the most grievous category, called type I or Werdnig-Hoffman disease, characterized with important muscle weaknesses, hypotonia and respiratory failures leading to death. Two highly similar genes, SMN1 and SMN2 encoding the SMN protein, are associated with the disease. They are located on the chromosome 5q13 and can present multiple copies. SMN1 is crucial for disease onset as in 95% of SMA patients the SMN1 gene is deleted, and/or is converted to SMN2. SMN1 conversion to its homologous gene is caused by a silent mutation in the exon 7 of SMN1 (c.840C>T), which leads to exclusion of exon 7 and the expression of a less stable SMN protein rapidly degraded. New therapeutic drugs have shown promising results when treatment is started early in infancy (less than 6 months), SMN1 new-born screening is essential to rapidly detect and treat SMA.