Individual estimates of age at detectable amyloid onset for risk factor assessment

INTRODUCTION: Individualized estimates of age at detectable amyloid-beta (Aβ) accumulation, distinct from amyloid positivity, allow for analysis of onset age of Aβ accumulation as an outcome measure to understand risk factors. METHODS: Using longitudinal Pittsburgh compound B (PiB) positron emission tomography data from Baltimore Longitudinal Study of Aging, we estimated the age at which each PiB+ individual began accumulating Aβ. We used survival analysis methods to quantify risk of accumulating Aβ and differences in onset age of Aβ accumulation in relation to APOE ε4 status and sex among 36 APOE ε4 carriers and 83 noncarriers. RESULTS: Age at onset of Aβ accumulation for the APOE ε4- and ε4+ groups was 73.1 and 60.7, respectively. APOE ε4 positivity conferred a threefold risk of accumulating Aβ after adjusting for sex and education. DISCUSSION: Estimation of onset age of amyloid accumulation may help gauge treatment efficacy in interventions to delay symptom onset in Alzheimer's disease.