For the decades-long search to understand why Huntington's disease (HD) destroys specific brain circuits, a new neuroimaging study offers a precise in vivo map of tau protein abnormalities — a mechanism previously understood mainly through post-mortem tissue. This matters because tau dysregulation may represent an actionable secondary target distinct from the primary huntingtin mutation, potentially broadening the therapeutic window for intervention.
Using the second-generation tau-PET tracer [¹⁸F]PI-2620 and dynamic 60-minute acquisition protocols in 54 participants spanning healthy controls, premanifest mutation carriers, and manifest HD patients, the study quantified tau-sensitive signal via distribution volume ratios derived from reference-tissue kinetic modelling. The globus pallidus emerged as the dominant site of abnormality, showing elevated DVR values that appeared before symptom onset in premanifest carriers and approached saturation in manifest disease. The putamen showed additional subcortical involvement, while the caudate — paradoxically — exhibited decreased DVR in manifest HD. Cortical tau changes were comparatively modest and concentrated in posterior associative regions. Cumulative genetic burden modelling confirmed largely monotonic subcortical progression, with limbic and cortical regions displaying more variable cross-sectional profiles.
This finding is analytically significant because it decouples tau pathology from the canonical cortical-dominant patterns seen in Alzheimer's disease, positioning HD as a subcortical tauopathy with a distinct spatiotemporal fingerprint. The early globus pallidus signal in premanifest carriers is particularly noteworthy — it suggests tau dysregulation precedes clinical onset and may be detectable during the window where neuroprotection is most feasible. However, the cohort of 54 participants limits statistical power for subgroup analyses, and cross-sectional design prevents causal inference about progression rates. Whether the [¹⁸F]PI-2620 signal in HD truly reflects tau aggregation versus off-target binding to mutant huntingtin aggregates also warrants longitudinal validation. Overall, this is an incrementally paradigm-shifting contribution that reframes HD biomarker strategy and opens a credible path toward tau-targeted clinical trials.