AD patients showed a higher concentration of YKL-40 compared with control subjects (Table 1) and the concentration increased also with older age (P = 0.01) (Additional file 1: Table 2), while the concentration of YKL-40 was found to be decreased in VNTR expansion carriers as opposed to non-carriers (medianexpansion+  = 150 ng/mL, medianABCA7- = 201 ng/mL, P = 0.0036, Table 2, Fig. 1). Here, CHI3L1 is linked to Alzheimer disease.