The relative reduction in striatal DAT in PSP may be due to the relative severity of axonal dysfunction or downregulation of DAT at the presynaptic terminal, although we cannot rule out the possibility that CSF HVA values are increased due to differences in the dopamine turnover (Kish et al. 1985; Palermo and Ceravolo 2019), reduction in delivery from the brain into the CSF (Rapoport et al. 2004), or dopamine levels outside the nigrostriatal pathway (Ruberg et al. 1985). The gene discussed is SLC6A3; the disease is supranuclear palsy, progressive, 1.