SLC18A2 and Parkinson disease: In contrast to PD patients, striatal levels of aromatic amino acid decarboxylase (AADC), dopamine transporter (DAT), and vesicular monoamine transporter 2 were normal in the two symptomatic cases with GTPCH-deficient DRD (Cases 1 and 2), indicating that dopaminergic terminals in the striatum are preserved in this disorder38); an age- related decline of putaminal BP during adulthood could contribute to late-onset parkinsonism recognized in Case 235, 56, 57).