SMN1 and proximal spinal muscular atrophy: Spinal muscular atrophy (SMA) is a rare genetic, neuromuscular disease (incidence of 1:6.000 to 1:10.000 births/year) characterized by the degeneration of alpha motor neurons in the spinal cord due to loss or dysfunction of the SMN-1 gene 5q11-q13 [3].