Early onset Alzheimer’s shows more tau accumulation

Clinical takeaway: Consider Alzheimer’s disease in patients younger than 65 who present with language, visuospatial, or executive dysfunction rather than prominent memory loss.

Clinicians who see a patient under 65 with failing language or visuospatial difficulties rarely think of Alzheimer’s disease first. Younger-onset disease often looks different, with dysexecutive, visuospatial, or language-led syndromes in place of the memory loss that dominates later onset. Any difference in the biology of patients under 65 is hard to read, because they arrive more impaired and heavier tau could mean a later look at the same disease.

Imaging studies have pointed to more tau in younger-onset disease, but they were small and mostly cross-sectional. That left unsettled whether disease stage explained the difference. With anti-amyloid antibodies now approved for early symptomatic disease, the answer could help clarify who benefits most and when. This study extends the evidence with a longitudinal comparison of tau scans in younger-onset and older-onset disease, adjusted for patients' level of impairment at the initial scan.

Younger-onset patients carried more tau than older-onset patients across frontal, temporal, and parietal cortices, at both the mild cognitive impairment and dementia stages. In the mesial temporal lobe, tau overlapped substantially between groups. Nearly three in four younger-onset patients were already at the dementia stage against just over one in three older-onset patients. Higher tau held after adjusting for amyloid burden and impairment.

Tau accumulated more rapidly in younger-onset patients across every region measured. The difference persisted after adjusting for baseline tau and at both clinical stages, though the older-onset dementia group was small. In older-onset patients tau increased mainly in the temporoparietal cortex and did not change in the frontal lobe, while younger-onset tau spread across much of the cortex. Modeling estimated that older-onset patients took years longer to reach comparable tau levels.

Tau tracked clinical impairment in both groups, but more steeply in younger-onset patients in every region except the mesial temporal lobe. The tau-amyloid link split the same way, steeper in younger-onset patients in the broad cortical measure but not the mesial temporal region. Neither apolipoprotein E ε4 status nor sex altered the age-group differences.

The analysis compared 390 patients with symptom onset before 65 from the Longitudinal Early-Onset Alzheimer’s Disease Study (LEADS) with 211 older patients from the Alzheimer’s Disease Neuroimaging Initiative (ADNI), all amyloid-positive with mild cognitive impairment or dementia. ADNI did not reliably record symptom onset, so older-onset meant 65 or older at the baseline scan. As a result, age and cohort effects cannot be fully separated. Follow-up scans covered 245 younger-onset and 99 older-onset patients, averaging 2.06 years in LEADS and 2.80 in ADNI. A check in 25 ADNI patients under 65 found tau levels between the two groups.

The authors suggest that younger-onset disease may be a useful setting for testing drugs that target tau. Faster tau accumulation and a stronger association to impairment could allow proof-of-concept trials to be conducted with smaller sample sizes. Patients with early-onset Alzheimer's disease remain underrepresented in clinical trials, in part because age cutoffs and memory-focused eligibility criteria exclude many of them. Whether earlier treatment with amyloid-targeting therapies provides greater benefit in this group was not addressed in this study. That hypothesis instead stems from prior trials in which higher baseline tau burden was associated with less treatment benefit.

“Developing a deeper understanding of the similarities and differences in AD pathophysiology across the age spectrum will advance our ability to identify optimal therapeutic approaches,” concluded the authors.

Source: Chiotis K, et al. (2026 Nov 4) Sci Transl Med. Distinct tau PET dynamics in early versus late age-of-onset Alzheimer’s disease