ROC curve analysis demonstrated that the human GPR37 NL-based ELISA assay could differentiate PD subjects (n = 41) from NCs (n = 45), with the area under the curve (AUC) of 0.808 (0.713–0.900) (P < 0.0001) (Fig. 4b). The gene discussed is GPR37; the disease is Parkinson disease.