SMN1 and proximal spinal muscular atrophy: Spinal Muscular Atrophy 5q, which will be referred to in the text simply as SMA for historical reasons related to the use of the acronym, is caused by pathogenic variants in the survival motor neuron 1 (SMN1) gene, resulting in a marked reduction of SMN protein production, which is essential for the proper function of spinal motor neurons.