Peptides corresponding to the following biomarkers were identified as the seven strongest predictors of group membership when separating the groups on neurochemical diagnosis (AD profile-positive; AD profile-negative): osteopontin, YKL-40, MDH, vitronectin, total apoE, limbic system-associated membrane protein and cystatin C. Osteopontin and YKL-40 also topped the list for cohort 1 (data not shown). The gene discussed is CHI3L1; the disease is Alzheimer disease.