Later polyGR RAN proteins were shown to be expressed from the C9orf72 G4C2•G2C4 repeat expansion mutation and accumulate as aggregates in the brain and spinal cord of amyotrophic lateral sclerosis and frontotemporal dementia (C9-ALS/FTD) patients [5, 65, 120]. Here, C9orf72 is linked to frontotemporal dementia.