Alzheimer disease (AD) remains biologically defined by amyloid-β (Aβ) plaques and tau neurofibrillary tangles, yet the clinical presentation is heterogeneous. While typical AD most commonly presents with prominent memory impairment, atypical AD variants present primarily with non-memory deficits. Reported atypical phenotypes include posterior cortical atrophy, the logopenic variant of primary progressive aphasia, behavioural and dysexecutive AD, and corticobasal syndrome. These variants are characterized by early visual, language, behavioural, executive and/or motor and praxis symptoms despite the same underlying core AD pathology.
Biological confirmation of AD is usually achieved through Aβ biomarkers, which establish AD status. However, the distribution and burden of regional tau pathology, downstream neurodegeneration and functional dysfunction more closely correlate with the clinical syndrome. The authors emphasise that co-pathologies and molecular modifiers — for example those related to immune–glial function, vascular health, synaptic integrity or protein handling — can influence the clinical expression of AD beyond total Aβ and tau load. The source notes that these additional biological contexts can alter regional vulnerability and potentially the pace of decline.
Regional heterogeneity in tau and neurofibrillary tangle topography underlies the different clinical syndromes. The review integrates neuropathological and imaging evidence showing that distinct AD clinical variants exhibit characteristic regional patterns of tau accumulation, atrophy and dysfunction. These patterns map onto large-scale brain networks and correspond to the predominant clinical deficits. Atypical AD variants therefore serve as human models to study why certain neuronal populations and circuits are selectively vulnerable while others are relatively spared in individual patients.
Tempo refers to the rate at which clinical symptoms and biomarkers evolve. Atypical AD variants tend to present at a younger age than typical AD, and tempo can vary across phenotypes and individuals. The authors propose that tempo is influenced not only by total pathological burden but also by genetic background, co-pathologies and molecular states such as immune–glial or vascular alterations. The review highlights that current biomarker frameworks for amyloid, tau and neurodegeneration confirm AD biology but do not fully capture tempo, which is clinically important for prognosis and trial design.
Because atypical AD presents with focal or network-predominant dysfunction despite global AD pathology, these variants offer opportunities to dissect mechanisms of selective vulnerability. Studying patients with younger onset and atypical topographies allows researchers to test hypotheses about modifiers of regional vulnerability, including genetic factors, immune–glial responses, vascular contributions, synaptic resilience and protein-handling pathways. The source positions atypical AD as a window into how the same core pathologies can produce divergent clinical pictures depending on regional and molecular context.
To better capture heterogeneity, the authors propose a practical multi-axis framework comprising four recorded dimensions: clinical phenotype, AD biological context (AD pathology plus co-pathologies and molecular modifiers), network topography (regional patterns of pathology and dysfunction) and tempo (rate of progression). Implementing this framework could reduce diagnostic mismatches between clinical impression and underlying biology, make cohorts more comparable across studies, and support clinical trials that include outcome measures tailored to the affected networks. The framework is intended to integrate clinical, neuropathological, imaging, genetic and molecular evidence to describe atypical AD within the broader AD spectrum.
The source material summarises conceptual advances and milestones in atypical AD research and includes figures illustrating complementary approaches to neurofibrillary tangle topography, the proposed multi-axis framework and a timeline of research milestones. The previewed content does not include full methodological detail, quantitative outcomes, or specific trial recommendations; those details were not reported in the provided source excerpt.