C9orf72 and amyotrophic lateral sclerosis: The identification of C9ORF72 repeat expansion as the major factor responsible for ALS onset in the familial forms has focused attention on the causative role of alterations in RNA metabolism [33,34,35], a line of research supported also by the involvement of mutations in TARDBP and FUS genes (encoding DNA/RNA binding proteins) in ALS development [36].