C9orf72 and frontotemporal dementia: Three neurodegenerative mechanisms are implicated in C9ORF72-ALS/FTD pathology: loss of function due to reduced C9ORF72 transcript and proteins levels [2], a gain of function due to the formation of RNA foci [46], and a gain of toxic function, due to the generation and accumulation of five different dipeptide repeat proteins (DPRs), via repeat-associated non-AUG (RAN) translation of hexanucleotide repeat sequences from both sense and antisense strands [20].