GRN and frontotemporal dementia: The discovery that gene mutations in GRN are linked to frontotemporal dementia (FTD), also described pathologically as frontotemporal lobar degeneration (FTLD) [13,14,15], and to one of the types of the lysosomal storage disease neuronal ceroid lipofuscinosis (NCL) [16,17] inspired many studies on the basic biology of PGRN and its clinical significance.