SLC6A3 and Parkinson disease: However, some patients with parkinsonism and normal DAT imaging have been reported to both have abnormal scans on follow-up and respond well to dopaminergic therapy [159,160], raising the possibility that DAT-SPECT can be normal in the very early phase of PD [161,162] and challenging the concept of normal DAT-SPECT as an absolute exclusion criterion [6].