Furthermore, to confirm that Fis1 is critical for the mitochondrial structural changes observed in ALS patient‐derived fibroblasts, we transiently knocked down the expression Fis1 (Fig EV1A) and observed a significant recovery in mitochondrial structure as measured by previously described methods (Figs 1A and EV1B and C). Here, FIS1 is linked to amyotrophic lateral sclerosis.