Several studies using newly developed methodologies have reported that APPsα CSF and blood plasma levels are unchanged in sporadic AD patients (Olsson et al., 2003; Perneczky et al., 2011, 2013; Rosén et al., 2012; Brinkmalm et al., 2013) with decreases only in advanced AD (Rosén et al., 2012) and in AD patients carrying the ApoE-ε4 allele (Olsson et al., 2003). Here, APOE is linked to Alzheimer disease.