C9orf72 and amyotrophic lateral sclerosis: The most common genetic causes identified until now account for about 70% of familial ALS and include expansions of a hexanucleotide repeat in chromosome 9 open reading frame 72 (C9orf72), involved in endosomal trafficking and autophagy; mutations in superoxide dismutase 1 (SOD1), encoding an antioxidant enzyme; and transactive response DNA binding protein 43 (TARDBP) and fused in sarcoma (FUS), which encode the DNA/RNA binding proteins TDP43 and FUS, respectively.