SMN1 and proximal spinal muscular atrophy: Spinal Muscular Atrophy (SMA) is a rare autosomal recessive disorder that causes progressive proximal muscle weakness and paralysis due to the degeneration of alpha motor neurons in the spinal cord and brainstem caused by biallelic variants in the survival motor neuron 1 (SMN1) gene on the long arm of chromosome 5q [1].