These data argue that mutant FUS toxicity does not involve an excess of FUS activity, as suggested by the finding that mutations in the 3′UTR of FUS13 cause ALS by perturbing the autoregulation of FUS expression60 and increasing FUSWT levels13, and by previous studies showing that overexpression of FUSWT is toxic to neurons. This evidence concerns the gene FUS and amyotrophic lateral sclerosis.