C9orf72 and amyotrophic lateral sclerosis: FTLD and ALS show important genetic overlap with mutations identified in the same genes, e.g., the common G4C2 repeat expansion in the chromosome 9 open reading frame 72 gene (C9orf72) and less frequently, mutations in the valosin containing protein (VCP), fused in sarcoma (FUS), TAR DNA-binding protein (TARDBP) and ubiquilin 2 (UBQLN2) genes [5, 8, 30, 31, 37].