Notably, the lowered levels of total TDP-43 in the FTD-TDP group were strongly driven by the C9-HRE genotype and FTD-MND phenotype indicating that mainly C9-HRE and FTD-MND-related TDP-43 pathophysiology (TDP type B pathology in C9-HRE carriers and FTD-MND patients vs. TDP type A pathology in GRN mutation carriers) is reflected to the total TDP-43 serum levels measured with Simoa assay. The gene discussed is C9; the disease is frontotemporal dementia.