C9orf72 and amyotrophic lateral sclerosis: Together, this recent work suggests that DNAm could possibly represent an epigenetic disease modifier, not necessarily at the level of the whole genome, but on relevant promoters and regulatory regions such as the C9ORF72 repeat expansion in C9-ALS patients or the auto-regulatory element of TARDBP in the vast majority of sALS and fALS patients.