Our results confirmed that while [F-18]-MK-6240 avidly bound to PHF-tangle containing slices from AD brains, it did not bind to a significant extent to tau-containing lesions in slices from non-AD tauopathy brains, suggesting that this tracer has higher affinity and selectivity for PHF-tau over tau aggregates with a primarily straight filament ultrastructure, and thus raising reasonable doubts about the potential value of this ligand as a biomarker of tau pathology in non-AD tauopathies. The gene discussed is MAPT; the disease is Alzheimer disease.