Tale of two diseases: amyotrophic lateral sclerosis and frontotemporal dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) were independently described in clinical and pathological details more than a century ago. Recent breakthrough discoveries identifying common genes that are causal to either ALS or FTD or an overlapping ALS-FTD syndrome have dramatically transformed our view regarding their pathogenesis. Most recently, a massive hexanucleotide (GGGGCC) repeat expansion mutation in C9orf72 gene has been linked to the majority of familial ALS, FTD and mixed ALS-FTD cases. C9orf72 and other genes causal to ALS and FTD are consistently associated with the formation of cellular RNA inclusions and protein aggregates. This article summarizes the recently reported ALS-FTD-linked genes and the emerging common unifying mechanism in the pathogenesis of ALS-FTD spectrum disorders along with a comment on the potential new therapeutic targets in these hitherto incurable diseases.