In this study we showed how (GGGGCC)n can arrange into mG4s via a combination of biophysical tools: CD demonstrating the formation of G4-structures, AGE confirming the formation of multimolecular species, and both NMM staining and KCl titrations providing further evidence to support the formation of mG4 species in C9orf72 expansion repeats characteristic of ALS/FTD. Here, C9orf72 is linked to amyotrophic lateral sclerosis.