Reduced levels of C9orf72 mRNA have been reported in post‐mortem tissue, patient‐derived lymphoblast cell lines and iPSNs and in blood samples (DeJesus‐Hernandez et al, 2011; Cooper‐Knock et al, 2012; Gijselinck et al, 2012, 2015; Belzil et al, 2013; Ciura et al, 2013; Donnelly et al, 2013; Mori et al, 2013b; Xi et al, 2013) and reduced C9orf72 protein levels were detected in the frontal cortex of ALS and FTD cases (Waite et al, 2014; Xiao et al, 2015), suggesting haploinsufficiency may contribute to C9ALS/FTD by a loss‐of‐function mechanism. The gene discussed is C9orf72; the disease is frontotemporal dementia.