GRN and early-onset autosomal dominant Alzheimer disease: SORT1 polymorphisms have been linked to PGRN levels in serum, as well as altered susceptibility to FTD and Alzheimer’s disease (McMillan et al., 2014; Andersson et al., 2016; Philtjens et al., 2018; Tönjes et al., 2018), suggesting a key role of SORT1 in the regulation of PGRN levels.