KLK4 and Alzheimer disease: As shown in Fig. 1, the plasma level of KLK4, and GSN in the AD group (4.74 ± 1.47 ng/ml, and 32.33 ± 4.23 μg/ml, P < 0.01) were significantly higher than those in the control group (3.70 ± 1.15 ng/ml and 26.62 ± 4.57 μg/ml,).