In patients with PD, correlation analysis showed that serum NFL levels were significantly positively correlated with motor symptom severity, measured with UPDRS III score and H-Y stage (UPDRS III score: r = 0.79, 95% CI 0.70–0.86, p < 0.001; Bonferroni corrected p < 0.01; Pearson correlation analysis; H-Y stage: r = 0.86, 95% CI 0.78–0.91, p < 0.001; Bonferroni corrected p < 0.01; Spearman correlation analysis) (Fig. 3A, Fig. 2A). The gene discussed is NEFL; the disease is Parkinson disease.