C9orf72 and frontotemporal dementia: A substantial body of evidence from neuropsychology, neuroimaging, and postmortem studies has demonstrated varying degrees of frontotemporal involvement (Burke, Elamin, et al., 2016; Chipika, Christidi, et al., 2020; Christidi et al., 2019; McKenna, Corcia, et al., 2021), and the clinical overlap between ALS and frontotemporal dementia (FTD) has been cemented by the discovery of shared genetic variants such as hexanucleotide repeat expansion in C9orf72 (Li Hi Shing, McKenna, et al., 2021).