APOE and Alzheimer disease: Studies have described the relationship between YKL-40 and AD (occurrence of increased YKL-40 expression areas, concentrating mainly on astrocytes surface, around amyloid plaques and blood vessels, with amyloid angiopathy in patients with AD brain [46]), and the relationship between APOE4 genotype and YKL-40 concentration in cerebrospinal fluid (CSF) [47].