MAPT and neurodegenerative disease: Pathogenic proteins associated with most neurodegenerative diseases have been detected in exosomes secreted into the extracellular space by cultured cells or in vivo, including mHTT (Jeon et al., 2016; Zhang et al., 2016; Deng et al., 2017), Aβ (Rajendran et al., 2006), tau (Simón et al., 2012; Asai et al., 2015), α-synuclein (Emmanouilidou et al., 2010), SOD1 (Grad et al., 2014), and TDP-43 (Iguchi et al., 2016).