Levels of C9ORF72 protein were investigated in frontal cortices of FTD patients (with or without ALS) carrying C9ORF72 expansions (n = 21), patients with non-genetic FTD, pathologically characterized by TDP-43-positive neuronal inclusions (n = 10), and neurologically normal controls (n = 12) determined by pathologists within the network of the NeuroCeb brain bank. Here, C9orf72 is linked to frontotemporal dementia.