C9orf72 and amyotrophic lateral sclerosis: Both familial and sporadic cases are associated with pathogenic variants in known ALS-linked genes, including superoxide dismutase 1 (SOD1), TAR DNA binding protein (TARDP) encoding for TDP-43, hexanucleotide expansion of chromosome 9 open reading frame 72 (C9orf72), fused in sarcoma (FUS), and optineurin (OPTN) [79,81].