In a murine AD model, deletion of the YKL-40-encoding gene CHI3L1 decreased amyloid plaque burden, suggesting that YKL-40 promotes Aβ accumulation.39 Indeed, a variant in the human CHI3L1 gene that results in decreased CSF YKL-40 expression is associated with slower AD progression.39 Our findings support blood YKL-40 elevation as part of the AD-specific pathologic cascade in both early and more clinically advanced disease. The gene discussed is CHI3L1; the disease is Alzheimer disease.