Differential survival with Alzheimer disease

There is considerable interest in examining the incidence, prevalence, and course of Alzheimer disease (AD) among persons of different race/ethnicity, and among those living in different locations, with the hope of identifying alternative factors that may be risks for or protect against this illness. The article by Mehta et al.¹ in the current issue of Neurology® reports differences in duration of disease that are somewhat unexpected: African Americans, who on average have a shorter lifespan than US whites, appear to live longer with AD.

This article raises certain disquieting issues. Why should there be ethnic differences in survival in dementia? Is this an artifact of the methodology, or is this finding telling us something basic about the disease? The paper utilizes an important resource—data from the National Alzheimer's Coordinating Center (NACC). This very substantial database of nearly 40,000 (as of the summer of 2007) patients with AD enabled the investigators to analyze information on a larger and more diverse sample than any single site could provide, and so identify notable differences in the impact of AD on persons of different race/ethnicity. The investigators worked with the data that were available, and analyzed these data carefully. But how adequate were those data? What standards should be applied to data submitted to a registry? Are the desired standards attainable? Even their sample size of over 30,000 does not preclude biases in recruitment and retention of subjects that could affect the findings.

There has long been interest in AD, but particular focus and funding can be dated to …