SMN2 and proximal spinal muscular atrophy: Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disease that is characterized by deficiency in the survival motor neuron (SMN) protein, often the result of the deletion of gene SMN1, that leads to progressive muscle weakness (Burghes and Beattie, 2009; Kolb and Kissel, 2015; Lunn and Wang, 2008; Tizzano and Finkel, 2017).