Emerging clinical trials focusing on preclinical Alzheimer's disease (AD) are expected to be most effective in the earliest or even prodromal stages of illness, before significant multi-system degeneration has occurred. To that end, it is critical to the success of emerging clinical trials to be able to identify and target individuals that are truly at-risk for AD. Reliably identifying these at-risk individuals; however, is currently cost prohibitive in large-scale trials given the reliance on AD biomarkers such as amyloid imaging to increase confidence in the diagnostic determination. To facilitate the feasibility of preclinical AD trials, the field must develop clinical outcome measures that are validated to identify early disease states with high levels of sensitivity and specificity. This approach in turn, would be significantly cost effective and has the potential to ultimately optimize clinical trial enrollment. Outcome measures must also be effective in measuring potential changes in treatment response over time, be related to biomarkers of early AD pathology (e.g., amyloid load, tau deposition, volumetric loss in AD prone regions on MRI), and be cross-culturally applicable given the growing Hispanic population in the United States. Our laboratory has been at the forefront of developing assessment paradigms that are both sensitive and specific to preclinical AD. One such novel memory paradigm, the LASSI-L taps the failure to recover from proactive semantic interference (frPSI) and has been shown to be significantly more sensitive to early cognitive deficits than learning inefficiency or simple rate of forgetting as is measured by the ADAS-Cog. The LASSI-L has also outperformed other widely used measures in detecting preclinical AD. More specifically, frPSI has been observed in otherwise cognitively normal elders with high amyloid load and decreased volumes in AD prone regions among elders with amnestic MCI (aMCI) and PreMCI suggesting that this paradigm represents a cognitive marker of very early AD. We have now significantly expanded our earlier work to develop a computerized Cognitive Stress Test (CST), designed to more strongly elicit cognitive markers of preclinical AD. In the current study, we intend to validate this novel and more powerful CST for use in preclinical AD trials by examining the performance of 240 Hispanic and non-Hispanic individuals with early stage MCI (eMCI) as compared to elders with no cognitive impairment and in relation to traditional measures employed in AD clinical trials such as the ADAS-Cog, longitudinally. We will also examine the relatedness of the CST to biological markers of AD: PET amyloid load, MRI measures of volume and cortical thickness, DTI and tau burden. The proposed investigation will provide an unparalleled opportunity to validate and establish a novel and promising cognitive outcome measure specifically designed to detect preclinical AD, for use in preclinical AD trials as both potential screening and outcome measures. We strongly believe that this can result in critical contributions to the field.
The Cognitive Stress Test is an empirically designed clinical outcome measure to detect cognitive decline in preclinical Alzheimer's disease (AD). This study proposes to validate its use for preclinical AD clinical trials in a well-defined cohort of at-risk individuals, and compare its utility to the Alzheimer's Disease Assessment Scale (ADAS-Cog), the most widely used clinical outcome measure in AD clinical trials. In addition, we will examine its relationship to biological markers of incipient AD such as total and regional brain amyloid load, tau load, and MRI regional atrophy.
