C9orf72 and frontotemporal dementia: By using immunofluorescence (IF) microscopy and a G-quadruplex recognizing antibody (BG-4), it was shown that G-quadruplexes formed by the expanded GGGGCC repeats in mutant C9orf72 RNAs exist and are components of pathogenic RNA foci observed in fibroblasts and astrocytes derived from C9ALS/FTD patients; they are also major components of insoluble protein/RNA aggregates that have been isolated from disease-relevant regions of post-mortem c9ALS brains.