GRN and Alzheimer disease: Furthermore, an AD‐associated GRN variant (rs5848), which causes a decrease in PGRN levels in plasma and CSF (Rademakers et al, 2008; Nicholson et al, 2014; Morenas‐Rodríguez et al, 2015), is associated with increased CSF T‐tau levels in participants of the ADNI study (Takahashi et al, 2017).