Assessment of associations of known AD risk factors and the medial temporal and orbitofrontal lobes a volumetric MRI study

Abstract

Title from first page of PDF file (viewed November 19, 2010)Includes bibliographical references (p. 49-59)Alzheimers disease (AD) has been recognized as the most common type of dementia in the United States affecting more than 4.5 million people, as measured by the 2000 census, and the prevalence is expected to increase exponentially over the next 50 years. AD is a progressive form of dementia that is marked by cognitive decline and cortical atrophy caused by neuritic plaques and neurofibrillary tangles. The neuropathology of AD can precede clinical symptoms by years, and thus widespread anatomical alterations can be present well before behavioral symptoms are noted. Therefore, pre-clinical diagnosis of AD has become an increasingly important line of research with aims to treat the disease before detrimental functional effects have occurred. The present study investigated the associations between known AD risk factors including age, education, and genetic status as well as the correlate of diminished olfactoryprocessing. Each of 39 older participants (aged 62 to 88) were tested on several risk factors including age, education levels, and APOE E4 status as well several indices of cognitive (Dementia Rating Scale, California Verbal Learning Test, and Boston Naming Test) and olfactory (Odor Threshold, Odor Identification, California Odor Learning Test, and Alcohol Sniff Test) processing. Anatomical MRI scans were also taken which were utilized in a volumetric MRI study. Areas that were segmented include the olfactory bulbs, entorhinal cortex, amygdala, hippocampus, orbitofrontal cortex, and a control region, the primary visual cortex. It was found that: (1) group analysis based on APOE E4 status revealed lower volumes on average for APOE E4+ subjects in the entorhinal cortex, hippocampus, amydala, and orbitofrontal cortex compared to APOE E4- subjects, (2) olfactory measures were significant predictors of the underlying volumes of the medial temporal lobe structures, (3) olfactory measures provide significant associations with MTL volumes beyond cognitive measures, and (4) predictive models of the hippocampus and entorhinal cortex change based on APOE E4 status