Our findings showing decreased, rather than increased, total TDP-43 levels in the serum of FTD patients with suspected TDP-43 pathology are in line with a previous study that assessed both total TDP-43 and pTDP-43 in a small cohort of genetic FTD patients, including ten C9-HRE carriers and five GRN mutation carriers [14]. Here, C9 is linked to frontotemporal dementia.