In a more recent multi-center prospective natural history study of 116 symptomatic C9orf72 ALS and 12 non-symptomatic C9orf72 repeat expansion carriers, it was revealed that the CSF concentrations of poly-GP DPRs remained high and steady over time in C9orf72 ALS patients [13]. Here, C9orf72 is linked to amyotrophic lateral sclerosis.