Numerous PET studies have compared some combination of fluorine-18-L-dihydroxyphenylalanine (FD), reflecting aromatic amino-acid decarboxylase activity and DA storage, a DAT and a VMAT2 radioligand in the same PD patients [5], [7], [28], [29] with inconsistent findings. The gene discussed is SLC6A3; the disease is Parkinson disease.