SMN1 and proximal spinal muscular atrophy: Spinal muscular atrophy (SMA) is a rare neurodegenerative disease that affects approximately 1 in 10,000 newborns, caused by insufficient synthesis of the survival motor neuron (SMN) protein, which occurs in 95% of cases due to a biallelic deletion in the SMN1 gene (5q13) [8,9].