VCP and amyotrophic lateral sclerosis: Beyond some established and distinct disease-causing genes, which account for a limited proportion of familial and, to a lesser extent, sporadic cases [i.e., progranulin (GRN), microtubule-associated protein tau (MAPT), tank-binding kinase 1 (TBK1), valosin containing protein (VCP), and charged multivesicular body protein 2B (CHMP2B) for FTD; TAR DNA binding protein (TARDBP), fused in sarcoma (FUS) and superoxide dismutase 1 (SOD1) for ALS] [7,9,10,11,12,13,14,15], most FTD and ALS forms show a still unclear multifactorial etiology.