In early drug-naïve PD patients, SV2A loss has been observed in the caudate, putamen, thalamus, brainstem and dorsal raphe, as well as cortical regions [58], with SV2A loss also reported in the substantia nigra in treated PD patients [191,192] and additional SV2A loss in the red nucleus and locus coeruleus in moderate to advanced PD patients [191]. This evidence concerns the gene SV2A and Parkinson disease.