MAPT and early-onset autosomal dominant Alzheimer disease: The role of exosomes in exporting amyloidogenic proteins from brain cells in neurodegenerative proteinopathies has been demonstrated in recent years by multiple groups who showed that CNS-derived exosomes may be enriched in amyloidogenic proteins, such as tau and hyperphosphorylated tau in Alzheimer's disease (AD) and other tauopathies (Clavaguera et al., 2009; Liu et al., 2012; Vella et al., 2016), monomeric and oligomeric amyloid β-protein (Aβ) in AD (Fiandaca et al., 2015; Sardar Sinha et al., 2018), and α-synuclein in Parkinson's disease (PD) (Danzer et al., 2012).