GRN and frontotemporal dementia: Therefore, we have determined PGRN levels in the CSF of patients with different forms of FTD and compared them with other forms of dementia in this study to investigate whether different CSF biomarker constellations mirror the supposed histopathological differences in FTD patients and especially differences between TDP43-mediated FTDs on one hand and the Tau-/ Fused in Sarcoma Protein (FUS)-mediated FTDs on the other.