C9orf72 and amyotrophic lateral sclerosis: Our finding that this subset of miRNAs was already downregulated in serum of presymptomatic carriers of causative ALS mutations (SOD1, C9orf72, and PFN1; [64]), as well as in FUS mutant iPSC-derived motoneurons that most likely represent a presymptomatic or early stage of the disease, may indicate an involvement of the FXPs in very early pathogenic mechanisms.