Taken together, the histological analyses of human post-mortem brains demonstrate that while TRPV1 and VGLUT2 expression is low in both control and PD midbrain, the strong GRP expression remains in the PD midbrain: GRP can thereby be used as a new and selective marker for the non-melanized DA neurons that are neuroprotected in PD. This evidence concerns the gene GRP and Parkinson disease.