APOA1 and Alzheimer disease: From the proposed candidate cerebrospinal fluid biomarkers for schizophrenia (Table 2), APOA1, APOA4, APOE, and PTGDS have been also proposed as candidate biomarkers for Alzheimer's disease and TTR (synthesized in the brain uniquely by choroid plexus, Herbert et al., 1986) as a candidate biomarker for Parkinson's and Alzheimer's diseases (Korolainen et al., 2010; Kroksveen et al., 2011).