C9orf72 and frontotemporal dementia: Indeed, ALS and FTD display significant clinical and genetic overlap and are now considered to be on a spectrum; lesions in several genes, including TAR-DNA binding protein 43 (TDP-43) and chromosome 9 open reading frame 72 (c9ORF72), can cause ALS, FTD, or both (Abramzon et al., 2020).