Primary age-related tauopathy.

Primary age-related tauopathy (PART) was proposed in 2014 as a neuropathological term to describe patients with Alzheimer's-type medial temporal lobe neurofibrillary degeneration in the absence of significant β-amyloid pathology. Over the past decade, this designation has gained widespread adoption, helping to clarify the interpretation of biomarker profiles, delineate early-stage tauopathy in aging, and differentiate non-Alzheimer tauopathies from aging and classical Alzheimer disease. This review revisits PART ten years following its conception, critically evaluating its neuropathological features, clinical correlates, molecular underpinnings, and current limitations. We synthesize recent advances in neuroimaging, biomarkers, genetics, and epidemiology, explore the relationship between PART and other age-associated neurodegenerative processes, and propose revisions to the original PART criteria. While PART has served as a valuable framework for studying tau pathology in aging, key questions remain regarding its pathogenesis, clinical significance, and relationship to the broader spectrum of tauopathies. We highlight major gaps in knowledge and outline priorities for future research aimed at defining the mechanisms, biomarkers, and clinical criteria that will determine whether PART represents a distinct disease or a universal feature of human brain aging.