Clinical trials for gene therapy in ALS patients, including those with superoxide dismutase-1 (SOD1) mutations, C9orf72 hexanucleotide repeat amplification, ATXN2 trinucleotide amplification, fused in sarcoma (FUS) mutations, and sporadic cases without a known genetic cause, are currently underway. Here, C9orf72 is linked to amyotrophic lateral sclerosis.