GRN and early-onset autosomal dominant Alzheimer disease: Finally, PGRN polymorphisms contribute to the risk of Alzheimer’s disease (AD) (Kamalainen et al, 2013; Perry et al, 2013; Sheng et al, 2014; Xu et al, 2017), and serum PGRN levels are inversely proportional to the risk of AD development (Hsiung et al, 2011).