A twisted, uncertain path has led to a U.S. FDA approval for Biogen Inc.’s Qalsody (tofersen), the first drug targeting a genetic cause of amyotrophic lateral sclerosis (ALS). Qalsody is for ALS associated with a mutation in the superoxide dismutase 1 (SOD1) gene. Patients with SOD-1 mutations account for 2% of ALS cases.