CHI3L1 and Alzheimer disease: Chi3l1 is a glycoprotein expressed by astrocytes and immune cells and has previously been suggested as a CSF biomarker of physiological aging and AD pathology, although little is known about its specific function.49–51 Because genetic deletion of Chi3l1 suppresses formation of amyloid plaques by increasing glial Aβ phagocytosis,52 present findings suggest that sleep loss could aggravate Aβ accumulation through the upregulation of this protein.