APOE and Alzheimer disease: We finally screened out acid ceramidase (Asah1) as a key protein in lipid metabolism and four other proteins specific to Aβ pathology, including clusterin, apolipoprotein E, neprilysin (Mme), and angiotensin converting enzyme (ACE), which contributes to uncovering the pathophysiology of AD and provides a new insight into the study of early diagnosis of AD.