MAPT and early-onset autosomal dominant Alzheimer disease: However, in human subjects of the Alzheimer’s Disease Neuroimaging Initiative (ADNI), the GRN rs5848 AD risk variant, which causes at least 10–20% reduction of PGRN protein levels, has no significant effects on florbetapir PET amyloid imaging or cerebrospinal fluid (CSF) Aβ levels, whereas it is associated with increased CSF tau levels [52], suggesting a potential effect of PGRN deficiency on tau pathology, rather than amyloid pathology.