Pathogenic variants in the superoxide dismutase 1 (SOD1) gene were the first identified genetic cause of amyotrophic lateral sclerosis (ALS), in 1993. This discovery enabled the development of transgenic rodent models for studying the biology of SOD1 ALS. The understanding that SOD1 ALS is driven by a toxic gain-of-function mutation has led to therapeutic strategies that aim to lower concentrations of SOD1 protein, an endeavour that has been complicated by the phenotypic heterogeneity of SOD1 ALS. The successful development of genetically targeted therapies to reduce SOD1 expression, together with a better understanding of pre-symptomatic disease and the discovery of neurofilament light protein as a susceptibility/risk biomarker that predicts phenoconversion, has ushered in a new era of trials that aim to prevent clinically manifest SOD1 ALS. The 30-year journey from gene discovery to gene therapy has not only uncovered the pathophysiology of SOD1 ALS, but has also facilitated the development of biomarkers that should aid therapy development for all forms of ALS.