fMRI as an Imaging Biomarker for Preclinical Alzheimer's Disease

Cleveland Clinic Lerner Com-Cwru, Cleveland OH

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Abstract

Biomarkers for early detection of Alzheimer's disease (AD) and for monitoring treatment response are becoming critically important as novel pharmacotherapeutics emerge. Several candidate biochemical, anatomical, and functional biomarkers have shown promise for identifying disease risk or treatment response potential, but vary in their efficacy and invasiveness. Among these candidate biomarkers, task-activated functional magnetic resonance imaging (fMRI) is a promising approach that is noninvasive, carries little risk, and offers a high potential for identifying persons who may eventually develop AD. The purpose of this investigation is to examine the value of task-activated fMRI in the identification and prediction of disease course in populations at-risk for the development of mild cognitive impairment (MCI) or AD. In specific Aim 1, we propose to examine the 4.5 year longitudinal course of 108 asymptomatic individuals with varying risk for conversion to MCI/AD based on the presence/absence of one or two apolipoprotein-E (APOE) [unreadable]4 alleles and/or a family history of dementia, and of 24 patients with amnestic MCI (aMCI), a condition strongly associated with conversion to AD. Primary measures include fMRI using a semantic memory activation task involving famous name recognition, neurobehavioral testing, and brain morphometry. We hypothesize that baseline levels of brain activation and longitudinal changes in activation will be the strongest predictor of cognitive decline. In Specific Aim 2, we propose to conduct a 24-week, randomized, double-blind, placebo-controlled, parallel group study of the Exelon(R) [rivastigmine] transdermal patch in 100 aMCI patients divided into two equal groups based on APOE [unreadable]4 status (positive versus negative). Task- activated fMRI will serve as the primary biomarker of treatment efficacy along with neuropsychological testing and brain morphometry as secondary endpoints. We hypothesize that the active treatment group will demonstrate a normalization (i.e. reduction) in the task-related neural activation pattern relative to the placebo group, and will be most evident for APOE [unreadable]4 positive MCI patients than in APOE [unreadable]4 negative MCI patients. These studies offer the opportunity to determine the role of fMRI as a biomarker for predicting future decline in the latent and prodromal phase of AD as well as for monitoring therapeutic outcome in clinical trials.