Conversely, in a patient with 2 SMN1copies, SMA diagnosis, related to SMN1 mutations is virtually excluded and other motor neuron disorders such as spinal muscular atrophy with respiratory distress (SMARD1), X-linked spinal muscular atrophy, distal SMA, and juvenile amyotrophic lateral sclerosis should be considered. This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.