Seed amplification assays can identify the biologically relevant aggregation-inducing proteopathic seeds antemortem, using amplification of minute amounts of seeds from accessible biofluids or tissues (Saborio et al., 2001; Wilham et al., 2010; Atarashi et al., 2011; Bongianni et al., 2017), in contrast to many other fluid biomarkers of neurodegeneration such as 14-3-3 and neurofilament light chain which are secondary markers of neural damage rather than underlying proteinopathy. Here, NEFL is linked to proteostasis deficiencies.