GPR37 and Parkinson disease: The GPR37 precursor density did not increase throughout the different Braak PD stages assayed, but the N-terminal-cleaved forms were significantly (P = 0.0057) increased at Braak PD stage 6 (Fig. 1b), rendering an average of 214% ± 42% increase of density (P = 0.0462) when all the GPR37 forms (i.e. precursor plus N-terminus cleaved forms) were considered (Fig. 1b).