SOD1 and amyotrophic lateral sclerosis: Over 20 years ago, Kaspar et al. used an AAV encoding the neurotrophic factor insulin-like growth factor 1 (IGF-1) to promote the synthesis of IGF-1 within the spinal motor neurons of ALS mice carrying the human SOD1 (hSOD1) mutant gene, successfully extending the survival of these mice [31].