When all sample values were included in the calculations, the average serum CDNF concentration in the PD patients was 40.3 ± 23.5 pg/ml (median: 38.1 pg/ml, n = 34), and in the controls it was 33.3 ± 12.9 pg/ml (median: 32.5 pg/ml, n = 35; Figure 2A). Here, CDNF is linked to Parkinson disease.