Amyloid‐PET, tau‐PET, and their association in sporadic early‐onset Alzheimer’s Disease: Cross‐sectional and longitudinal data from the LEADS study

Abstract

AbstractBackgroundWe aimed to describe amyloid‐ and tau‐PET in patients with sporadic Early Onset AD (sEOAD) from the Longitudinal Early‐onset Alzheimer’s Disease Study. We focused on amyloid‐tau relationships and on the association between i) age, sex, and ii) cross‐sectional and longitudinal PET measures.MethodsIn December 2022, we selected patients who fulfilled the following criteria: 1) clinical diagnosis of MCI or mild dementia, 2) available amyloid‐PET (18F‐florbetaben), tau‐PET (18F‐fortaucipir), and structural MRI, 3) positive amyloid‐PET based on a process including visual read and quantification. Image acquisition, quality control, and processing followed ADNI procedures. Florbetaben‐PET Centiloids and mean cortical Flortaucipir‐SUVR were extracted in native space using FreeSurfer. Cross‐sectional analyses were performed using general linear models; longitudinal analyses (up to 4 scans/patient) were performed using linear mixed effect models with random intercepts.ResultsOut of the 372 cognitively impaired patients included in LEADS, 280 (75.3%) were amyloid‐positive patients with sEOAD (Table 1 for demographics and clinical characteristics). Cross‐sectionally, Centiloids and cortical Flortaucipir‐SUVR were correlated (r = 0.29, p<.001; Fig 1a). Patient’s age was associated with cortical tau‐PET (older patients showing lower Flortaucipir‐SUVR, r = ‐0.47, p<0.001, Fig 1b) but not amyloid‐PET (r = ‐0.02, p = 0.68). Females showed greater amyloid (d = 0.43, p<0.001, Fig 1c) and tau‐PET burden (d = 0.35, p = 0.004), in the absence of sex differences in MMSE or CDR‐SB (d’s<0.16, p’s>0.37). Sex differences in tau‐PET remained significant (p = 0.04) when controlling for age and Centiloids. Both Centiloids and Flortaucipir‐SUVR increased longitudinally (p<0.001, Figure 3a‐b). The rate of Centiloid change was not modulated by age (time*age, p = 0.79) or sex (time*sex, p = 0.91). Changes in tau‐PET were independent of sex (time*sex, p = 0.15), but younger patients tended to show greater FTP‐SUVR progression (time*age, p = 0.07). In a subsample of 123 patients with at least 2 timepoints for both amyloid and tau‐PET (Fig 3c), rates of amyloid and tau changes were correlated (r = 0.22, p = 0.013).ConclusionIn patients with sEOAD, amyloid‐ and tau‐PET are modestly correlated at baseline and continue to increase together over time. In EOAD, younger age is associated with higher tau‐PET burden, independent of amyloid. Females show greater amyloid and tau burden than males despite similar clinical severity measures.