Biomarkers

Prior cross-sectional studies in the PREVENT-AD cohort indicate that increased concentrations of p-tau181 in cerebrospinal fluid are linked to impairments in odor identification (OI; Lafaille-Magnan et al., 2017) and central auditory processing (CAP; Tuwaig et al., 2017). However, the extent to which AD pathology is predictive of change in neurosensory impairments remains unclear. To clarify these relationships, we examined how OI and CAP differ, cross-sectionally and longitudinally, according to amyloid and tau (A/T) status based on PET. To support our findings, we replicated our results using baseline plasma A/T status.

We studied 233 participants from the PREVENT-AD cohort who had at least one value for each of the following measures: amyloid PET ([¹⁸F]NAV4694), tau PET ([18F]AV-1451), University of Pennsylvania Smell Identification Test (UPSIT), and Dichotic Sentence Identification test (DSI). Amyloid and tau PET thresholds were Centiloid=18 and SUVR=1.29, respectively. A partially overlapping subset of participants (n = 208) had values for plasma Aβ₄₂ and Aβ₄₀ concentrations measured using ultrasensitive immunoprecipitation coupled with mass spectrometry (IP-MS) technique. Plasma p-tau217 concentrations were quantified using the University of Gothenburg assay. Plasma amyloid positivity was determined by implementing a data-driven algorithm (Dumurgier et al., 2022). Kruskal-Wallis and Dunn's tests were conducted to assess baseline differences in olfaction and audition according to PET or plasma A/T status. Linear mixed effects models analyzed change over time in neurosensory abilities, by A/T group, while controlling for age, sex, and education.

For PET-based classification, A+T- exhibited lower OI scores than A-T- (Figure 1a). For plasma-based classification, A+T+ displayed lower OI scores than A+T- and A-T- (Figure 1c). Longitudinally, the rate of decline in OI was largest in A+T+, but this result was only significant for plasma (Figure 1g). No associations were found with CAP.

Our analyses suggest that the presence of pathological amyloid and tau (A+T+) is associated with declines in the neurosensory domain of odor identification. Future studies should examine whether similar trends are observed for other neurosensory domains such as vision and gustation.