SLC6A3 and Parkinson disease: Ponsen et al. (21) found in their prospective cohort study of 361 non-parkinsonian, non-demented first-degree relatives of PD patients, that a two-step approach of initial olfactory testing followed by dopamine transporter (DAT)- SPECT scanning in individuals with hyposmia strongly increases specificity while retaining the high sensitivity associated with olfactory testing alone.