Abstract
Background: Studies providing Alzheimer’s disease (AD) prevalence data have largely neglected to characterize the proportion of AD that is mild, moderate or severe. Estimates of the severity distribution along the AD continuum, including the mild cognitive impairment (MCI) stage, are important to plan research and allocate future resources, particularly resources targeted at particular stages of disease. Methods: Participants (aged 50-94) with prevalent MCI or AD dementia clinical syndrome were cross-sectionally selected from three time-windows of the population-based Framingham Heart Study in 2004-2005 (n=381), 2006-2007 (n=422), and 2008-2009 (n=389). Summary estimates of the severity distribution were achieved by pooling results across time-windows. Diagnosis and severity were assessed by consensus dementia review. MCI-progressive was determined if the participant had documented progression to AD dementia clinical syndrome using longitudinal data.Results: Among AD dementia participants, the pooled percentages were 50.4% for mild, 30.3% for moderate, and 19.3% for severe. Among all MCI and AD participants, the pooled percentages were 29.5%, 19.6%, 25.7%, and 45.2% for MCI-not-progressive, MCI-progressive, mild AD dementia, and the combined group of MCI-progressive & mild AD dementia, respectively. Distributions by age and sex were presented.Conclusions: Heterogeneity in severity of the AD population exists. That half of prevalent cases have mild disease underscores the need for research and interventions to slow decline of this burdensome disease.Limitations: First, the FHS cohort participants were almost homogenously Caucasians and residents of a single city in MA, that limits the generalization of the results. Second, although FHS is a longitudinal study, the study population over the three time-windows would not be expected to be as dynamic as that of sampling participants from different geographic areas. Lastly, the study lacked AD biomarker confirmation (e.g., amyloid, tau, neurodegeneration), which would have increased the accuracy of case ascertainment.
Risk Estimations, Risk Factors, and Genetic Variants Associated with Alzheimer's Disease in Selected Publications from the Framingham Heart Study
