Finding a radiological biomarker that correlates well with the underlying 4R tau pathology in vivo has been a challenge.7 Currently existing tau PET tracers exhibit higher binding affinity to Alzheimer-type paired helical filament-tau, consisting of three-repeat (3R) + 4R isoforms, over isolated 3R or 4R tau.8 Hence, the value of these tracers in 4R tauopathies is unclear. This evidence concerns the gene MAPT and tauopathy.