Unexpected similarities between C9ORF72 and sporadic forms of ALS/FTD suggest a common disease mechanism

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) represent two ends of a disease spectrum with shared clinical, genetic and pathological features. These include near ubiquitous pathological inclusions of the RNA binding protein (RBP) TDP-43, and often the presence of a GGGGCC expansion in the C9ORF72 (C9) gene. Here we show unexpectedly that the signature of hnRNP H sequestration and altered splicing of target transcripts we identified in C9ALS patients (Conlon et al. 2016) also occurs in fully half of 50 post-mortem sporadic, non-C9 ALS/FTD post-mortem brains. Furthermore, and equally surprisingly, these “like-C9” brains also contained correspondingly high amounts of insoluble TDP-43, as well as several other disease-related RBPs, and this correlates with widespread global splicing defects. Finally, we show that the like-C9 sporadic patients, like actual C9ALS patients, were much more likely to have developed FTD. We propose that these unexpected links between C9 and sporadic ALS/FTD define a common mechanism in this disease spectrum. Differential splicing analysis of Amyotrophic Lateral Sclerosis (ALS) and Control samples contributor: NYGC ALS Consortium contributor: The Target ALS Human Postmortem Tissue Core