Lower desmosterol levels have been previously found in the plasma and brains of AD patients compared with healthy controls.13, 26 Desmosterol is a precursor of cholesterol and seladin (DHCR24), which governs the metabolism of desmosterol to cholesterol in specific brain areas has been shown to counteract the β-secretase cleavage of APP and the formation of amyloid-β.37, 38 An unknown molecule with similar structure and the same mass as desmosterol shows the highest correlation with cholesterol here. Here, DHCR24 is linked to Alzheimer disease.