SystemsAge
SystemsAge is a multi-organ biological-age framework introduced by Tian and colleagues (2023, Nature Medicine) that uses longitudinal brain MRI and physiological/biomarker phenotypes from large biobanks (UK Biobank in the original paper) to generate organ-specific age estimates across 3 brain systems (cerebral cortex, thalamus, cerebellum) and 7 body systems (cardiovascular, respiratory, renal, gastrointestinal, liver, musculoskeletal, immune) — 10 systems total. Rather than a single composite score, it produces a profile of organ biological ages, allowing detection of discordant ageing across systems. In the UK Biobank, organ age gaps predicted organ-specific disease and all-cause mortality; individuals whose organ ages were globally younger than their chronological age showed lower mortality risk. A separate methylation-based 'SystemsAge' clock by Sehgal et al. 2025 Nature Aging (Levine lab) covers 11 physiological systems via a single blood-based assay; the two clocks share a name but use different inputs.
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