In addition, dopamine transporter single-photon emission computed tomography (DaT-SPECT) also explained that the high prevalence of olfactory loss in PD patients, as measured by the UPSIT, is due to the association of ODs with the pronounced loss of nigrostriatal dopamine neurons in the putamen and caudate nucleus [36]. The gene discussed is SLC6A3; the disease is Parkinson disease.