24S-HC and 27O hydroxycholesterol in the plasma indicates the degree of beta-amyloid production, loss of active grey matter, phosphorylated tau accumulation, and brain atrophy, thus indicating AD [11]. A case-control study by Popp et al., including 200 patients, found an association between increased plasma 24S hydroxycholesterol, 27O hydroxycholesterol, and AD [41]. The gene discussed is MAPT; the disease is Alzheimer disease.