OCA2 and Alzheimer disease: Its expression increased with the course of AD.[32] Ykl-40 is expressed in both astrocytes and microglia, and the specific mechanism leading to AD is still unclear.[33] During the preclinical, prodromal, and dementia stages of AD, YKL-40 levels in cerebrospinal fluid are elevated, accompanied by elevated T-tau and P-tau protein levels, especially in individual patients with significant Aβ deposits.