DKK1 and early-onset autosomal dominant Alzheimer disease: Studies have demonstrated a significant upregulation in the expression of Wnt signaling inhibitor proteins (such as DKK-1, SFRP-1, and SFRP-2) in postmortem AD brain and transgenic AD mouse models [52, 53].This upregulation effectively suppresses the Wnt signaling pathway in Alzheimer's disease (AD).