C9orf72 and amyotrophic lateral sclerosis: It is noteworthy that the protein C9ORF72, encoded by the most commonly-mutated gene in ALS, has been recently found to be structurally related to a GDP/GTP exchange factor (GEF) that activates Rab-GTPases [103] and to co-localize with Rab proteins, including Rab7, in neuronal cell lines, primary cortical neurons and human spinal cord motor neurons of ALS patients [97].