HSPG2 and primary progressive aphasia: Lastly, due to the low prevalence of the multiple and rare FTD variants and multisystem neurodegenerative disorders with different neuropathological substrates (TDP43, tauopathy, synucleinopathies), it is not possible to sort out the differences in PLC/PBA prevalence in conditions like three-in-one syndrome (PPA, corticobasal degeneration and frontal lobe dementia),69C9orf72with combined Multiple System Atrophy and ALS,70especially within different disease stages.