Persistent Functional Impairment as an Early Indicator of Alzheimer Disease Pathology and Progression.

BACKGROUND: Functional impairment (FI) is a key criterion for diagnosing dementia. However, subtle functional changes may occur during preclinical and prodromal phases but may not be accurately characterized. Furthermore, research linking FI to Alzheimer disease (AD) biofluid biomarkers is limited. Here we examined cross-sectional associations between cerebrospinal fluid (CSF) AD biomarkers and persistent versus transient FI in dementia-free older adults, and the longitudinal association of FI with incident dementia. METHODS: Data from 1000 participants (age 72.9 ± 7.0; 45.2% female; 62.8% MCI) from the Alzheimer's Disease Neuroimaging Initiative were analyzed. CSF biomarkers included p-tau181, Aβ42, and ptau-181/Aβ42 ratio. Three Functional Activities Questionnaire items of "preparing a hot beverage," "preparing a balanced meal," and "shopping alone" were identified by factor analysis as assessing function rather than cognition directly. Persistent-FI was operationalized as FI present at> two-thirds of pre-dementia visits. Comparator groups included Transient-FI and No-FI. Linear regression modeled the association between FI status and baseline biomarker levels, while Cox regression assessed the association between FI and incident dementia. Models adjusted for age, sex, education, APOE-ε4 status, and MMSE. RESULTS: Compared to No-FI, Persistent-FI was associated with lower Aβ42 (Beta = -8.93; 95% CI: -13.56 to -4.03; p < 0.001), higher p-tau181 (Beta = 10.81; 95% CI: 0.44-22.26; p = 0.041), and ptau181/Aβ42 ratio (Beta = 21.66; 95% CI: 7.02-38.31; p = 0.003). In contrast, Transient-FI showed no significant associations. APOE-ε4 carrier status was more prevalent in the Persistent-FI group compared to No-FI (p = 0.009), but not in Transient-FI (p = 0.931). Compared to No-FI, Persistent-FI had a 6.66-fold greater dementia incidence rate (95% CI: 4.98-8.91, p < 0.001), while Transient-FI had a 1.72-fold greater incidence rate (95% CI: 1.09-2.72, p = 0.021). CONCLUSIONS: Findings extend the limited research on the association of FI with CSF AD biomarkers in dementia-free populations. Operationalizing FI-related risk by persistence enhances prognostication, identifying individuals with greater AD pathology and progression risk. This approach could enhance screening, early detection, and risk stratification, informing timely interventions before dementia onset.