Amyloid-β-Associated Clinical Decline Occurs Only in the Presence of Elevated P-tau

Objective: To elucidate the relationship between the 2 hallmark proteins of Alzheimer disease (AD), amyloid-beta (A beta) and tau, and clinical decline over time among cognitively normal older individuals. Design: A longitudinal cohort of clinically and cognitively normal older individuals assessed with baseline lumbar puncture and longitudinal clinical assessments. Setting: Research centers across the United States and Canada. Patients: Weexamined 107 participants with a Clinical Dementia Rating (CDR) of 0 at baseline examination. Main Outcome Measures: Using linear mixed effects models, we investigated the relationship between cerebrospinal fluid (CSF) phospho-tau 181 (p-tau(181p)), CSF A beta(1-42), and clinical decline as assessed using longitudinal change in global CDR, CDR-Sum of Boxes, and the Alzheimer Disease Assessment Scale-cognitive subscale. Results: We found a significant relationship between decreased CSFA beta(1-42) and longitudinal change in global CDR, CDR-Sum of Boxes, and Alzheimer Disease Assessment Scale-cognitive subscale in individuals with elevated CSF p-tau(181p). In the absence of CSF p-tau(181p), the effect of CSF A beta(1-42) on longitudinal clinical decline was not significantly different from 0. Conclusions: In cognitively normal older individuals, A beta-associated clinical decline during a mean of 3 years may occur only in the presence of ongoing downstream neurodegeneration. Arch Neurol. 2012; 69(6): 709-713. Published online April 23, 2012. doi:10.1001/archneurol.2011.3354