MAPT and Alzheimer disease: We investigated whether 1) KL-VSHET is associated with lower AD biomarker burden (Aβ42, Aβ42/40 ratio, P-tau181, T-tau) and neurodegeneration (NfL); 2) sαKl relates to AD biomarkers, neurodegeneration (NfL), neuroinflammation (GFAP), and synaptic dysfunction (Ng); 3) associations vary by APOE ε4 status and clinical subgroup.