C9orf72 and amyotrophic lateral sclerosis: Motor neuron death in C9orf72-ALS is likely caused by the combined effects of (i) haploinsufficiency of the C9orf72 protein, (ii) gain of toxic function caused by the accumulation of G4C2 RNA into nuclear foci, and (iii) by RAN translation of G4C2 repeat RNA into aberrant DPRs [57,59,60].