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.